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Artichoke (Globe)

Recommendations for Maintaining Postharvest Quality

artichoke063
Trevor Suslow and Marita Cantwell

Department of Plant Sciences, University of California, Davis

Maturity & Quality

Maturity Indices

The edible bud, composed of a cone of bracts, is harvested at an immature stage and selected for size and compactness. Overdeveloped buds have an open or spreading structure; the bracts have a brownish cast and are tough and stringy; the centers have a fuzzy, pink to purple appearance.

Quality Indices

Quality indices are compact and well-formed buds, typical green color, a smooth and uniform stem-cut, freedom from insect damage or handling damage and defects. Artichoke buds should feel heavy for their size. Stems are generally cut 2.5 to 3.8 cm (1 to 1.5 in) below the base.

Maturity & Quality Photos

Title: Quality (1)

Photo Credit: Adel Kader, UC Davis 

Title: Quality (2)

Photo Credit: Adel Kader, UC Davis 

Temperature & Controlled Atmosphere

Optimum Temperature

0°C (32°F)

Hydrocooling, forced-air cooling, and package-icing are common methods of postharvest cooling of artichokes.

Storage potential of artichoke is generally less than 21 days as visual and sensory quality deteriorate rapidly.

Relative Humidity

>95% RH

Rates of Respiration

Temperature ml CO2/kg·hr
0°C (32°F) 8-22
5°C (41°F) 13-30
10°C (50°F) 22-49
15°C (59°F) 38-72
20°C (68°F) 67-126


To calculate heat production, multiply ml CO2/kg·hr by 440 to get BTU/ton/day or by 122 to get kcal/metric ton·day.

Rates of Ethylene Production

Very low;

Responses to Ethylene

Artichokes have a low sensitivity to exogenous ethylene and therefore it is not considered a factor in postharvest handling and distribution.

Responses to Controlled Atmospheres

Controlled or modified atmospheres offer moderate to little benefit to sustaining artichoke quality. Conditions of 2-3% O2 and 3-5% CO2 delay discoloration of bracts and the onset of decay by a few days at temperatures around 5°C (41°F). Atmospheres below 2% O2 may result in internal blackening of artichokes.

Disorders

Physiological and Physical Disorders

Freezing Injury. Freezing injury will be initiated at -1.2°C (29.9°F). Symptoms of light freezing injury are blistering of the cuticle and a bronzing of the outer bracts. This may occur in the field with winter harvested buds and is used in marketing as an index of high quality. More severe freeze injury results in watersoaked bracts and the heart becoming brown to black and gelatinous in appearance over time.

Bruising and Compression Injury. Very common when attention to careful harvest and handling practices are not followed.

Pathological Disorders

Grey Mold (Botrytis cinerea) and Bacterial Soft Rot (Erwinia carotovora) may be a problem in storage and distribution if optimum temperature conditions are not met. Opportunistic fungi (such as Fusarium spp.) may develop on cut stems or bracts with prolonged low temperature storage.

Date

November 1997

Asparagus (Green)

Recommendations for Maintaining Postharvest Quality

asparagus064
Trevor Suslow

Department of Plant Sciences, University of California, Davis

Maturity & Quality

Optimum Temperature

0°C-2°C (32°F-35.6°F)

Storage life is typically 14-21 days at 2°C and can be extended up to 31 days by 7-10 days storage at 0°C and atmospheric modification. Extended storage (~10-12 days) in air at 0°C may cause chilling injury.

Optimum Relative Humidity

95-100%

High relative humidity is essential to prevent dessication and loss of glossiness. Drying of the butt-end of spears is a negative quality factor. Commonly asparagus is packed and shipped in cartons with a water-saturated pad to maintain high humidity.

Rates of Respiration

Temp. 
°C (°F)
ml CO2/kg·hr
0 (32) 14-40
5 (41) 28-68
10 (50) 45-152
15 (59) 80-168
20 (68 138-250
25 (77) 250-300

To calculate heat production multiply ml CO2/kg·hr by 440 to get Btu/ton/day or by 122 to get kcal/metric ton/day.

Rates of Ethylene Production


Responses to Ethylene

Exposure to ethylene will accelerate the lignification (toughening) of asparagus spears in controlled studies. The concentration and duration of exposure to exogenous ethylene, to cause this effect, at commonly encountered levels during storage and distribution are not available.

Responses to Controlled Atmospheres (CA)

Elevated CO2 at 5-10% (typically 7%) in air is beneficial in preventing decay and reducing the rate of toughening of the spears. The beneficial effect is most pronounced if temperatures cannot be maintained below 5°C (41°F). Short (CA) exposure to higher CO2 concentrations (12-20%) is safe and beneficial only if temperatures can be maintained at 0°C-1°C (32°F-33.8°F).

Signs of CO2 injury are small to elongated pits, generally first observed just below the tips. Severe injury results in ribbiness.

Maturity & Quality Photos

Title: Asparagus Maturity

Photo Credit: Marita Cantwell, UC Davis

Temperature & Controlled Atmosphere

Optimum Temperature

0°C-2°C (32°F-35.6°F)

Storage life is typically 14-21 days at 2°C and can be extended up to 31 days by 7-10 days storage at 0°C and atmospheric modification. Extended storage (~10-12 days) in air at 0°C may cause chilling injury.

Optimum Relative Humidity

95-100%

High relative humidity is essential to prevent dessication and loss of glossiness. Drying of the butt-end of spears is a negative quality factor. Commonly asparagus is packed and shipped in cartons with a water-saturated pad to maintain high humidity.

Rates of Respiration

Temp. 
°C (°F)
ml CO2/kg·hr
0 (32) 14-40
5 (41) 28-68
10 (50) 45-152
15 (59) 80-168
20 (68 138-250
25 (77) 250-300

To calculate heat production multiply ml CO2/kg·hr by 440 to get Btu/ton/day or by 122 to get kcal/metric ton/day.

Rates of Ethylene Production


Responses to Ethylene

Exposure to ethylene will accelerate the lignification (toughening) of asparagus spears in controlled studies. The concentration and duration of exposure to exogenous ethylene, to cause this effect, at commonly encountered levels during storage and distribution are not available.

Responses to Controlled Atmospheres (CA)

Elevated CO2 at 5-10% (typically 7%) in air is beneficial in preventing decay and reducing the rate of toughening of the spears. The beneficial effect is most pronounced if temperatures cannot be maintained below 5°C (41°F). Short (CA) exposure to higher CO2 concentrations (12-20%) is safe and beneficial only if temperatures can be maintained at 0°C-1°C (32°F-33.8°F).

Signs of CO2 injury are small to elongated pits, generally first observed just below the tips. Severe injury results in ribbiness.

Disorders

Physiological and Physical Disorders

  • Asparagus will continue to develop after harvest which is why low temperature postharvest management is critical. Common disorders include upward bending of tips away from gravity and "feathering" (expansion and opening) of tips. Bending will also occur if tips expand to the top of the packaging and are deflected
  • Spear toughening occurs rapidly at temperatures above 10°C (50°F)
  • Bruising and tip-breakage are signs of rough handling and can result in toughening of the spears from wound ethylene
  • Asparagus is sensitive to chilling injury after 10 days at 0°C (32°F). Symptoms of chilling injury include loss of sheen or glossiness and graying of the tips. A limp, wilted appearance may be observed. Severe chilling injury may result in darkening near tips in spots or streaks
  • Freezing injury (water-soaked appearance leading to extreme softening) will likely result at temperatures of -0.6°C (30.9°F) or lower

Pathological Disorders

The most prominent postharvest disease concern is bacterial soft rot, induced by Erwinia carotovora subsp. carotovora. Decay may initiate at the tips or the butt end. Spears that are re-cut above the white portion of the butt end are reported to be most susceptible to bacterial decay.

Special Considerations

Rapid hydrocooling soon after harvest is strongly recommended. Pyramid-shaped wooden or waxed corrugated boxes for hydrocooling combined with center-loading during shipment promote good cooling-air circulation.

Disorders Photos

Title: Asparagus Bending

Photo Credit: Leonard Morris, UC Davis 

Title: Asparagus Flower Initiation

Photo Credit: CDFA 

Title: Bacterial Soft Rot on Asparagus Tips

Photo Credit:  Cantwell, Marita Department of Plant Sciences

Title: Broken Tips

Photo Credit: CDFA 

Title: Crooked Spears

Photo Credit: CDFA 

Title: Frozen and Thawed Asparagus

Photo Credit: CDFA 

Title: Split Spears

Photo Credit: CDFA 

Title: Wilting

Photo Credit: CDFA 

Date

August 1996

Bean, Snap

Recommendations for Maintaining Postharvest Quality

snapbeans066
Marita Cantwell and Trevor Suslow

Department of Plant Sciences, University of California, Davis

Beans, Snap PDF

Maturity & Quality

Optimum Temperature

5-7.5°C (41-45°F)

Very good quality can be maintained for a few days at temperatures below 5°C but chilling injury will be induced (see Physiological Disorders). Some chilling may occur even at the recommended storage temperature of 5°C after 7-8 days. At 5-7.5°C (41-45°F) a shelf-life of 8-12 days is expected.

Water loss is a common postharvest problem with green beans. About 5% weight loss is needed before shrivel and limpness are observed. After 10-12% weight loss, the beans are no longer marketable. The weight loss of mature green beans can be estimated from the equation: % weight loss per day = 0.754 x vapor pressure deficit. The VPD can be obtained from a psychrometric chart when temperature and relative humidity are measured. The rate of water loss of immature beans is higher than for mature beans.

Relative Humidity

95-100%

Rates of Respiration

Temperature ml CO2>/kg·hr
°C (°F) Snap Beans Long Beans
0 (32) 10 20
5 (41) 17 23
10 (50) 29 46
15 (59) 46 101
20 (68) 65 110

To calculate heat production, multiply ml CO2/kg·hr by 440 to get BTU/ton·day or by 122 to get kcal/metric ton·day.

Rates of Ethylene Production

Responses to Ethylene

Exposure to ethylene at usual storage temperatures causes loss of green pigment and increased browning. Concentrations above 0.1 ppm reduce green bean shelf-life by 30-50% at 5°C.

Responses to Controlled Atmospheres (CA)

At recommended storage temperature, O2 concentrations of 2-5% reduce respiration rates. Snap beans tolerate and are benefited by CO2 concentrations between 3-10%. The main benefit is retention of color and reduced discoloration on damaged beans. Higher CO2 (20-30%) concentrations can be used for short periods, but can cause off-flavors.

Maturity & Quality Photos

Title: Maturity

Photo Credit: Marita Cantwell, UC Davis  

Temperature & Controlled Atmosphere

Optimum Temperature

5-7.5°C (41-45°F)

Very good quality can be maintained for a few days at temperatures below 5°C but chilling injury will be induced (see Physiological Disorders). Some chilling may occur even at the recommended storage temperature of 5°C after 7-8 days. At 5-7.5°C (41-45°F) a shelf-life of 8-12 days is expected.

Water loss is a common postharvest problem with green beans. About 5% weight loss is needed before shrivel and limpness are observed. After 10-12% weight loss, the beans are no longer marketable. The weight loss of mature green beans can be estimated from the equation: % weight loss per day = 0.754 x vapor pressure deficit. The VPD can be obtained from a psychrometric chart when temperature and relative humidity are measured. The rate of water loss of immature beans is higher than for mature beans.

Relative Humidity

95-100%

Rates of Respiration

Temperature ml CO2>/kg·hr
°C (°F) Snap Beans Long Beans
0 (32) 10 20
5 (41) 17 23
10 (50) 29 46
15 (59) 46 101
20 (68) 65 110

To calculate heat production, multiply ml CO2/kg·hr by 440 to get BTU/ton·day or by 122 to get kcal/metric ton·day.

Rates of Ethylene Production

Responses to Ethylene

Exposure to ethylene at usual storage temperatures causes loss of green pigment and increased browning. Concentrations above 0.1 ppm reduce green bean shelf-life by 30-50% at 5°C.

Responses to Controlled Atmospheres (CA)

At recommended storage temperature, O2 concentrations of 2-5% reduce respiration rates. Snap beans tolerate and are benefited by CO2 concentrations between 3-10%. The main benefit is retention of color and reduced discoloration on damaged beans. Higher CO2 (20-30%) concentrations can be used for short periods, but can cause off-flavors.

Temperature & Controlled Atmosphere Photos

Title: Chilling Injury (1)

Photo Credit: Marita Cantwell, UC Davis  

Title: Chilling Injury (2)

Photo Credit: Marita Cantwell, UC Davis   

Title: Chilling Injury (3)

Photo Credit: Marita Cantwell, UC Davis

Disorders

Physiological and Physical Disorders

Chilling injury. The typical symptom of chilling injury in beans stored <5°C (<41°F) for longer than 5-6 days is a general opaque discoloration of the entire bean. A less common symptom is pitting on the surface. The most common symptom of chilling injury is the appearance of discrete rusty brown spots which occur in the temperature range of 5-7.5°C (41-45°F). These lesions are very susceptible to attack by common fungal pathogens. Beans can be held about 2 days at 1°C (34°F), 4 days at 2.5°C (36°F), or 8-10 days at 5°C (41°F) before chilling symptoms appear. No discoloration occurs on beans stored at 10°C (50°F). Different varieties differ significantly in their susceptibility to chilling injury.

Freezing injury. Appears as water-soaked areas which subsequently deteriorate and decay. Freezing injury occurs at temperatures of -0.7°C (30.7°F) or below.

Rough handling at harvest or damage from shipping containers can result in translucent areas that are susceptible to decay.

Pathological Disorders

Decay due to various pathogens occurs after beans have been chill damaged. Surface decay may also occur on stems and beans if free moisture is present during storage at >7.5 (>45°F). Common postharvest decay organisms on green beans are the fungi Pythium, Rhizopus, and Sclerotinia, all of which may occur as "nests" of decay or on broken or damaged beans.

Special Considerations

Haricot Verts. Extra careful handling is required for tender immature green beans or haricot verts to avoid physical damage and dehydration.

Long beans have similar postharvest requirements as green beans and similar responses to chilling temperatures. Long beans may yellow more and have more seed development during postharvest handling than snap beans.

Disorders Photos

Title: Anthracnose

Photo Credit: Marita Cantwell, UC Davis

Title: Botrytis Gray Mold

Photo Credit: Don Edwards, UC Davis 

Title: Physical Injury

Photo Credit: Marita Cantwell, UC Davis

Title: Sclerotinia Sclerotiorum (with apothecium)

Photo Credit:

Title: White Rot

Photo Credit: Don Edwards, UC Davis

Date

May 1998

Belgian Endive (Witloof Chicory)

Recommendations for Maintaining Postharvest Quality

belgianendive067
Marita Cantwell and Trevor Suslow

Department of Plant Sciences, University of California, Davis

Maturity & Quality

General Information

Witloof chicory or Belgian endive is a "chicon" or compact oval head of overlapping leaves produced from a harvested tap root. Forcing occurs in the dark at elevated temperatures 16-20°C (60-68°F) often in hydroponic trays and results in the cream-yellowish compact head or chicon after 3-4 weeks. Witloof chicory is a member of the lettuce family.

Maturity Indices

Maturity is based on chicon size and compactness and varies according to cultivar and the quality of the tap root (amount of carbohydrate reserves). The firm heads are harvested by snapping from the root. 

Quality Indices

Quality is based on size, compactness, shape, and color. After trimming outer leaves, the chicons should be white with closed cream-yellow points and not have any torn leaves. Witloof chicory cultivars vary in flavor and bitterness (caused by sesquiterpene lactones). Chicons rapidly turn green if exposed to light and the flavor changes (see Special Considerations). Good quality chicons do not have any traces of green but are white with cream-yellow leaf edges.

Maturity & Quality Photos

Title: Greening

Photo Credit: Marita Cantwell, UC Davis  

Temperature & Controlled Atmosphere

Optimum Temperature

0°C (32°F) is required to optimize witloof chicory storage and life. A shelf-life of 21-28 days can be expected at this temperature. At 5°C (41°F) a shelf-life of about 14 days can be expected. Witloof chicory is usually room cooled after packing. Placing chicons on ice for retail display will cause discoloration. 

Freezing Injury. Freeze damage weakens the leaves and can lead to more rapid bacterial decay. During storage, freeze damage can occur if chicons are stored at

Relative Humidity

>95%

Rates of Respiration

Belgian endive chicons have moderate respiration rates:

Temperature 0°C (32°F) 10°C (50°F) 20°C (68°F)
ml CO2/kg·hr 4-5 14-17 35-44

To calculate heat production, multiply ml CO2/kg·hr by 440 to get BTU/ton/day or by 122 to get kcal/metric ton-day.

Rates of Ethylene Production

Ethylene production rates of harvested chicons are <0.1, 0.2, and 0.7 µL/kg·hr at 0, 10 and 20°C (32, 50 and 68°F), respectively. 

Responses to Ethylene

Witloof chicory or Belgian endive is moderately sensitive to ethylene exposure. The main symptoms of ethylene injury are accelerated decay and discoloration of the leaf margins. Ethylene could also be expected to induce leaf abscission, but this effect may require a very long period at low storage temperatures. 

Responses to Controlled Atmosphere (CA)

Some benefit to shelf-life can be obtained with low O2 (3-4%) and high CO2 to (4-5%) atmospheres at temperatures of 0-5°C (32-41°F). CA retards the development of browning on leaf edges. CO2 atmospheres also retard discoloration of the butt also. To control greening, extremely low O2 concentrations (<0.1%) are required.

Disorders

Physiological and Physical Disorders

Internal Browning. The warm forcing conditions for witloof chicory production can cause browning of the chicon axis. This is thought to be due to a localized calcium deficiency in the rapidly developing head.

Physical Injury. Breakage of the outer leaf margins often occurs during harvest, trimming and packing and causes increased browning and increased susceptibility to bacterial decay. 

Pathological Disorders

Decay is not a common cause of postharvest losses of witloof chicory. However, bacterial rots caused by numerous bacteria (Erwinia, Pseudomonas and Xanthomonas spp.) can occur and result in a slimy breakdown of the infected tissue. Trimming outer leaves, rapid cooling and low storage temperature reduce development of bacterial rots. Sanitation during initial harvest, trimming and washing reduce bacterial decays. 

Special Considerations

Exposure to light causes the chicons to turn green and become unmarketable. Packaging in paper liners in unvented boxes ensures dark storage during distribution. However at retail, the chicons will turn green within a few hours at 10-15°C (50-59°F) of exposure to display lights. Therefore only a few should be removed from the box at a time to reduce exposure to light. Another option is to place the chicons in a plastic box with a lid that excludes light. If kept cold 0-5°C (32-41°F) it takes longer than 2 days for greening to occur.

Date

February 2001

Bell Pepper

Recommendations for Maintaining Postharvest Quality

bellpepper068
Marita Cantwell                                                                                        

Department of Plant Sciences, University of California, Davis

Maturity & Quality

Maturity Indices

Green Peppers: fruit size, firmness, color
Colored Peppers: minimum 50% coloration

Quality Indices

  • Uniform shape, size and color typical of variety
  • Firmness
  • Freedom from defects such as cracks, decay, sunburn

Maturity & Quality Photos

Title: Maturity

Photo Credit: Marita Cantwell, UC Davis  

Title: Ripeness Stages

Photo Credit: Marita Cantwell, UC Davis 

Temperature & Controlled Atmosphere

Optimum Temperature

Peppers should be cooled as soon as possible to reduce water loss. Peppers stored above 7.5°C (45°F) suffer more water loss and shrivel. Storage at 7.5°C (45°F) is best for maximum shelf-life (3-5 weeks); peppers can be stored at 5°C (41°F) for 2 weeks, and although this reduces water loss, chilling injury will begin to appear after that period. Symptoms of chilling injury include pitting, decay, discoloration of the seed cavity, softening without water loss. Ripe or colored peppers are less chilling sensitive than green peppers.

Optimum Relative Humidity

>95%; firmness of peppers is directly related to water loss

Rates of Respiration

Temperature 5°C (41°F) 10°C (50°F) 20°C (68°F)
ml CO2/kg·hr 3-4 5-8 18-20

To calculate heat production multiply ml CO2/kg·hr by 440 to get BTU/ton/ day or by 122 to get kcal/metric ton/day.

Rates of Ethylene Production

Bell peppers are nonclimacteric in behavior and produce very low levels of ethylene: 0.1-0.2 µl/kg·hr at 10°C-20°C (50°F-68°F).

Responses to Ethylene

Bell Peppers respond very little to ethylene; to accelerate ripening or color change, holding partially colored peppers at warm temperatures of 20-25°C (68-77°F) with high humidity (>95%) is most effective.

Responses to Controlled Atmospheres (CA)

Peppers generally do not respond well to CA. Low O2 atmospheres (2-5% O2) alone have little effect on quality and high CO2 atmospheres (>5%) can damage peppers (pitting, discoloration, softening) especially if they are stored below 10°C (50°F). Atmospheres of 3% O2 + 5% CO2 were more beneficial for red than green peppers stored at 5°C (41°F) to 10°C (50°F) for 3-4 weeks.

Temperature & Controlled Atmosphere Photos

Title: Chilling Injury Symptoms

Photo Credit: Adel Kader, UC Davis 

Title: Internal Discoloration

Photo Credit: Marita Cantwell, UC Davis  

Disorders

Physiological and Physical Disorders

Blossom End Rot. This disorder occurs as a slight discoloration or a severe dark sunken lesion at the blossom end; it is caused by temporary insufficiencies of water and calcium and may occur under high temperature conditions when the peppers are rapidly growing.

Pepper Speck. This disorder appears as spot-like lesions that penetrate the fruit wall; cause is unknown; some varieties are more susceptible than others.

Chilling Injury. Symptoms of chilling injury include surface pitting, water-soaked areas, decay (especially Alternaria), and discoloration of the seed cavity.

Mechanical damage. (crushing, stem punctures, cracks, etc.) This is very common on peppers; physical injury not only detracts from the visual quality of the peppers but also causes increased weight loss and decay.

Pathological Disorders

On California-grown bell peppers, the most common decay organisms are Botrytis, Alternaria, and soft rots of fungal and bacterial origin.

Botrytis or Grey mold decay. This is a common decay-causing organism on peppers; field sanitation and prevention of wounds on the fruit help reduce its incidence. Botrytis will grow well at the recommended storage temperatures. High CO2 levels (>10%) which can control Botrytis damage peppers. Hot water dips of peppers can effectively control Botrytis rot (55°C [130°F] water for 4 minutes) without causing fruit injury.

Alternaria Rot. The presence of black Alternaria rot, especially on the stem end of the pepper is a symptom of chilling injury; best control measure is to store at 7.2°C (45°F).

Bacterial Soft Rot. Soft rotting areas can be caused by several bacteria which attack damaged tissue; soft rots can also be common on washed or hydrocooled peppers where water sanitation was deficient.

[For more information, see our publication “ Fruit Ripening & Ethylene Management ”, available for purchase using our Publication order form .]

Disorders Photos

Title: Alternaria Rot

Photo Credit: Adel Kader, UC Davis 

Title: Bacterial Soft Rot

Photo Credit: Marita Cantwell, UC Davis

Title: Decay

Photo Credit: Marita Cantwell, UC Davis

Title: Greenhouse Pepper Defects

Photo Credit: Marita Cantwell, UC Davis

Title: Mechanical Damage and Decay

Photo Credit: Marita Cantwell, UC Davis

Title: Physical Damage

Photo Credit: Marita Cantwell, UC Davis

Title: Shriveling

Photo Credit: Marita Cantwell, UC Davis

Title: Solar Yellowing

Photo Credit: Marita Cantwell, UC Davis

Title: Sun Damage

Photo Credit: Marita Cantwell, UC Davis

Title: Sun Scald

Photo Credit: Marita Cantwell, UC Davis

Date

August 1996

Broccoli

Recommendations for Maintaining Postharvest Quality

broccoli069
Marita Cantwell and Trevor Suslow

Department of Plant Sciences, University of California, Davis

Maturity & Quality

Maturity Indices

Head diameter and compactness; all florets (beads) should be closed.

Quality Indices

Good quality broccoli should have dark or bright green closed florets. The head should be compact (firm to hand pressure), with a cleanly cut stalk of the required length. There should be no yellow florets and there should be no discoloration on the stem bracts.

Maturity & Quality Photos

Title: Color Rating

Photo Credit: Don Edwards, UC Davis 

Title: Color vs. Pigment

Photo Credit: Marita Cantwell, UC Davis 

Title: Maturity Stages

Photo Credit: Marita Cantwell, UC Davis 

Title: Stem Discoloration Scale

Photo Credit: Marita Cantwell, UC Davis 

Title: Yellowing Scale

Photo Credit: Marita Cantwell, UC Davis

Temperature & Controlled Atmosphere

Optimum Temperature

Low temperature is extremely important to achieve adequate shelf-life in broccoli. A temperature of 0°C (32°F) is required to optimize broccoli storage life (21-28 days). Heads stored at 5°C (41°F) can have a storage life of 14 days; storage life at 10°C (50°F) is about 5 days. Broccoli is usually rapidly cooled by liquid-icing the field-packed waxed cartons. Hydrocooling and forced-air cooling also can be used, but temperature management during distribution is more critical than with iced broccoli.

Freezing Injury. Broccoli will freeze if stored at -0.6°C (30.6°F) to -1.0°C (30°F). This may also occur if salt is used in the liquid-ice cooling slurry. Frozen and thawed areas on the florets appear very dark and translucent, may discolor after thawing and are very susceptible to bacterial decay.

Optimum Relative Humidity

>95%

Rates of Respiration

Broccoli heads have relatively high respiration rates:

Temperature 0°C (32°F) 5°C (41°F) 10°C (50°F) 15°C (59°F) 20°C (68°F)
ml CO2/kg·hr 10-11 16-18 38-43 80-90 140-160

The respiration rates of florets are slightly more than twice the rates of the intact heads.
To calculate heat of production multiply ml CO2/kg·hr by 440 to get Btu/ton-day or by 122 to get kcal/metric ton-day.


Rates of Ethylene Production

Very low,

Responses to Ethylene

Broccoli is extremely sensitive to exposure to ethylene. Floret yellowing is the most common symptom. Exposure to 2 ppm ethylene at 10°C (50°F) reduces shelf-life by 50%.

Responses to Controlled Atmospheres (CA)

Broccoli can be benefitted by 1-2% O2 with 5-10% CO2 atmospheres at a temperature range of 0-5°C (32-41°F). Although under controlled conditions such low O2 levels extend shelf-life, temperature fluctuations during commercial handling make this risky as broccoli can easily produce offensive sulfur-containing volatiles. As a result, a high rate of air exchange is recommended in standard marine container shipments of broccoli. Most modified atmosphere packaging for broccoli is designed to maintain O2 at 3-10% and CO2 at about 7-10% to avoid the development of these undesirable off-odor volatiles.

Temperature & Controlled Atmosphere Photos

Title: Ethylene Induced Yellowing of Broccoli

Photo Credit: Don Edwards, UC Davis 

Title: Ethylene Yellowing

Photo Credit: Michael Reid, UC Davis 

Title: Temperature and Ethylene Effects

Photo Credit: Marita Cantwell, UC Davis 

Title: Temperature and Modified Atmosphere Effects

Photo Credit: Marita Cantwell, UC Davis 

Disorders

Physiological and Physical Disorders

Hollow Stem. An open area in the stem at the cut surface which may become discolored and decay; growing conditions and variety selection affect development of this disorder.

Floret (bead) Yellowing. The florets are the most perishable part of the broccoli head; yellowing may be due to overmaturity at harvest, high storage temperatures, and/or exposure to ethylene. Any development of yellow beads ends commercial marketability. Bead yellowing due to senescence should not be confused with the yellow-light green color of areas of florets not exposed to light during growth, sometimes called "marginal yellowing".

Brown Floret (bead). Is a disorder in which areas of florets do not develop correctly, die and lead to brown discolored areas. This is thought to be caused by plant nutritional imbalances.

Rough handling at harvest can damage the florets and increase decay.  The force used to apply the water-ice slurry for cooling can also damage the florets on the heads and increase susceptibility to bacterial decay.

Pathological Disorders

Bacterial decay. Various soft-rot causing organisms (Erwinia, Pseudomonas) may affect broccoli shelf-life. Rots due to these organisms are usually associated with physical injury.

Fungal pathogens. Although not as common as bacterial rots, gray mold rot (Botrytis cinerea) and black mold (Alternaria spp.) can infect broccoli heads; this may occur under rainy, very cool growing conditions.

Special Considerations

Storage life varies considerably among broccoli cultivars. Shelf-life (appearance of any yellow beads = end of shelf-life) may vary from 12 to >25 days depending on cultivar: Shelf-life of different broccoli cultivars stored at 5°C (41°F), and 95% RH:

  • Short (
  • Moderate (20 to 25 days): Cascade, Embassy, Emperor, Esquire, Galaxy, Gem, Green Lady, Green Valiant, Hi Caliber, Midori #8, Pinnacle, Sakata #12, Schooner, Southern Comet, Vantage
  • Long (>25 days): Citation, Galaxy, Glacier, Greenbelt, Legacy, Marathon, Mercedes, Packman, Pirate, Premium Crop, Shogun, Skiff

Disorders Photos

Title: Bacterial Soft Rot

Photo Credit: Marita Cantwell, UC Davis 

Title: Botrytis Decay

Photo Credit: Marita Cantwell, UC Davis

Date

November 1997

Brussels Sprouts

Recommendations for Maintaining Postharvest Quality

brussels sprouts016
Marita Cantwell and Trevor Suslow

Department of Plant Sciences, University of California, Davis

Maturity & Quality

Maturity Indices

Brussels sprouts are the compact vegetative buds that develop along the stem of the Brussels sprouts plant. They should be harvested when the buds are firm, but not overmature which is indicated by splitting of the outer leaves.

Quality Indices

Good quality Brussels sprouts should be bright green, without yellowing or discoloration, and have a firm texture. The butt end may be slightly discolored, but should not be dark. Brussels sprouts should be sweet and mild in flavor when cooked. Bitterness varies among cultivars and is associated with high concentrations of specific glucosinolates (sinigrin and progoitrin). Bitterness can also be induced by storage conditions (see Responses to Controlled Atmospheres).

Temperature & Controlled Atmosphere

Optimum Temperature and Relative Humidity

Brussels sprouts are moderately perishable and can be stored 3-5 weeks at temperatures near the optimum of 0°C (32°F). Shelf life at 5°C (41°F) is 10-18 days and at 10°C (50°F) is less than 7 days. Brussels sprouts are often hydrocooled, but can be air cooled as well. Although they have considerable wax on their leaves, they become flaccid due to water loss if high relative humidity is not maintained. 

Freezing Injury. Brussels sprouts freeze at about -0.6°C (30.9°F). Slight freeze damage on the outer leaves of buds may result in small dark and translucent areas. Severe freeze damage results in the entire bud becoming dark and translucent, and very soft after thawing.

Optimum Relative Humidity

>95%

Rates of Respiration

Brussels sprouts have relatively high respiration rates. The highest rate at each temperature corresponds to measurements within 1-2 days of harvest.

Temperature 0°C (32°F) 5°C (41°F) 10°C (50°F) 15°C (59°F) 20°C (68°F)
ml CO2/kg·hr 5-15 11-24 20-40 30-50 45-75

To calculate heat production, multiply ml CO2/kg·hr by 440 to get BTU/ton/day or by 122 to get kcal/metric ton-day.

Rates of Ethylene Production

Ethylene production rates are slightly higher than those of other green and leafy vegetables, but can still be classified as low:

Responses to Ethylene

Brussels sprouts are sensitive to exposure to ethylene. Leaf yellowing and leaf abscission are the most common symptoms of ethylene injury. 

Responses to Controlled Atmosphere (CA)

Brussels sprouts can be benefited by 1-4% O2 with 5-10% CO2 atmospheres at 2.5-5°C (32-41°F). The main benefits are reduced yellowing and decay, reduced butt discoloration and inhibition of ethylene production. No benefits of CA are observed if the Brussels sprouts are kept at their optimum storage temperature 0°C (32°F). Low oxygen storage (<1%) can cause extreme bitterness and may also cause internal discoloration. Atmospheres of 10-12% CO2 can result in off-flavors and off-odors.

Disorders

Physiological and Physical Disorders

Freezing Injury. Brussels sprouts freeze at about -0.6°C (30.9°F). Slight freeze damage on the outer leaves of buds may result in small dark and translucent areas. Severe freeze damage results in the entire bud becoming dark and translucent, and very soft after thawing.

Puffiness. Or lack of firmness is undesirable in the buds and may vary among cultivars and growing conditions.

Internal browning. Can occur under very wet production conditions and is associated with condensation on the developing leaves. 

Physical Injury. Rough handling at harvest can bruise the buds and increase decay. 

Pathological Disorders

Brussels sprouts are not very prone to postharvest decay, but may be affected by the same organisms that infect other Brassica vegetables. Bacterial decay due to various soft-rot causing organisms (Erwinia, Pseudomonas) may infect sprouts, but bacterial decay is usually associated with physical injury. Less common are fungal pathogens, which can occur under rainy and cool growing conditions.

Disorders Photos

Title: Internal Browning

Photo Credit: Don Edwards, UC Davis

Date

February 2001

Cabbage (Round & Chinese types)

Recommendations for Maintaining Postharvest Quality

cabbage008
Marita Cantwell and Trevor Suslow

Department of Plant Sciences, University of California, Davis

Maturity & Quality

General Information

Round hard cabbages and Chinese (also called Napa) cabbages are from the same genus (Brassica) but different species (B. oleracea var capitata = cabbage, B. campestris var. pekinensis = Chinese cabbage). Chinese cabbages may be cylindrical or rounded and may be less compact than round cabbages. Information mentioned here applies to both types unless stated otherwise.

Maturity Indices

Maturity is based on head compactness. A compact head can be only slightly compressed with moderate hand pressure. A very loose head is immature, and a very firm or hard head is mature.

Quality Indices

After trimming outer wrapper leaves, cabbage heads should be a color typical of the cultivar (green, red, or pale yellow-green), firm, heavy for the size and free of insect, decay, seed stalk development and other defects. Leaves should be crisp and turgid. For round cabbages, grades are U.S. No. 1 and U.S. commercial.

Temperature & Controlled Atmosphere

Optimum Temperature

Most cabbage is room cooled. Storage at 0°C (32°F) is required to optimize cabbage storage life. Early crop round cabbage can be stored 3-6 weeks, while late crop cultivars can be stored for up to 6 months. For the latter, storage at -0.5°C (31°F) is sometimes recommended. Chinese cabbage can be stored from 2 to 6 months, depending on cultivar, at 0°C to 2.5°C (32°F to 36°F). Deterioration of cabbage during storage is associated with stem or seed stalk growth (bolting), root growth, internal breakdown, leaf abscission, discoloration, decay and black speck. Long-term storage usually results in extensive trimming of heads to remove deteriorated leaves.

Freezing Injury. Freeze damage appears as darkened translucent or water-soaked areas that will deteriorate rapidly after thawing. Freeze damage can occur if round cabbages are stored below -0.9°C (30.4°F) and if Chinese cabbage is stored below -0.6°C (31°F).

Optimum Relative Humidity

>95%

Rates of Respiration

Round and Chinese cabbages have similar moderately low respiration rates:

Temperature 0°C (32°F) 5°C (41°F) 10°C (50°F) 15°C (59°F) 20°C (68°F)
ml CO2/kg·hr 2-3 4-6 8-10 10-16 14-25

To calculate heat production multiply mL CO2/kg·hr by 440 to get Btu/ton/day or by 122 to get kcal/metric ton/day.
Respiration rates of shredded cabbage are 13-20 mL CO2/kg·hr at 5°C (41°F).

Rates of Ethylene Production

Ethylene production rates are generally very low:

Responses to Ethylene

Cabbages are sensitive to ethylene, which causes leaf abscission and leaf yellowing. Adequate ventilation during storage is important to maintain very low ethylene levels. Ethylene does not increase the disorder "black speck" or "pepper spot".

Responses to Controlled Atmospheres (CA)

Some benefit to shelf-life can be obtained with low O2 (2.5-5%) and high CO2 (2.5-6%) atmospheres at temperatures of 0-5°C (32-41°F). CA storage will maintain color and flavor of cabbage, retard root and stem growth, and reduce leaf abscission. O2 atmospheres below 2.5% for round cabbage and 1% for Chinese cabbage will cause fermentation, and CO2 atmospheres >10% will cause internal discoloration.

Temperature & Controlled Atmosphere Photos

Title: Ethylene-Induced Yellowing

Photo Credit: Don Edwards, UC Davis

Disorders

Physiological and Physical Disorders

Black speck. Black leaf speck (also called pepper spot, petiole spot, gomasho) is a disorder that consists of very small to moderate size discolored lesions on the midrib and veins of the leaves. The symptoms can occur after low temperatures in the field and by harvesting overmature heads, but are usually associated with transit and storage conditions. Low storage temperatures followed by warmer temperatures enhance development. Ethylene does not promote development of black speck in Chinese cabbage. Both round and Chinese cabbage cultivars vary widely in their susceptibility to this disorder. Storage with high CO2 atmospheres (10%) can reduce pepper spot development on round cabbage.

Chilling injury. In Chinese cabbage is purported to occur during storage at 0°C (32°F) after 3 months or longer. The main symptom is midrib discoloration, especially on outer leaves. Cultivars differ greatly in their susceptibility to develop midrib discoloration.

Physical Injury. Breakage of the midribs often occurs during field packing and causes increased browning and increased susceptibility to decay. Outer midribs of overmature heads will crack easily.

Pathological Disorders

The most common decays found in stored cabbage are watery soft rot (Sclerotinia), gray mold rot (Botrytis cinerea), alternaria leaf spot (Alternaria spp.), and bacterial soft rot (caused by various bacterial species including Erwinia, Pseudomonas, Xanthomonas). Bacterial soft-rots result in a slimy breakdown of the infected tissue, and may follow fungal infections. Trimming outer leaves, rapid cooling and low temperature storage reduce development of these rots, although Botrytis and Alternaria will grow at low storage temperatures.

Special Considerations

Fresh-cut or shredded cabbage pieces brown during storage and atmospheres of 3-5% O2 and 5-15% CO2 retard discoloration. Too low oxygen levels lead to fermentation and package blow-up, especially if product is not held below 5°C (41°F).

Date

August 2001

Carrot

Recommendations for Maintaining Postharvest Quality

carrots071
Trevor V. Suslow, Jeffrey Mitchell and Marita Cantwell

Department of Plant Sciences, University of California, Davis

Maturity & Quality

Maturity Indices

  • In practice, harvest decisions for carrots are based on several criteria depending on the market outlet or sales endpoint
  • Typically carrots are harvested at an immature state when the roots have achieved sufficient size to fill in the tip and develop a uniform taper
  • Length may be used as a maturity index for harvest timing of ‘cut and peel' carrots to achieve a desired processing efficiency

Quality Indices

There are many visual and organoleptic properties that differentiate the diverse varieties of carrots for fresh market and minimal processing. In general, carrots should be:

  • Firm (not flacid or limp)
  • Straight with a uniform taper from ‘shoulder' to ‘tip'
  • Bright orange
  • There should be little residual "hairiness" from lateral roots
  • No "green shoulders" or "green core" from exposure to sunlight during the growth phase
  • Low bitterness from terpenoid compounds
  • High moisture content and high reducing sugars are most desireable for fresh consumption

U.S. Grades:

  • Bunched Carrots - No. 1 and Commercial Grade
  • Topped Carrots - Extra No. 1, U.S. No. 1, No. 1 Jumbo, No. 2

Quality Defects include lack of firmness, non-uniform shape, roughness, poor color, splitting or cracking, green core, sunburn, and poor quality of tops or trimming.

Maturity & Quality Photos

Title: Carrots with Tops

Photo Credit: Adel Kader, UC Davis

Temperature & Controlled Atmosphere

Optimum Temperature

0°C (32°F)

Storage life at 0°C is typically:

  • Bunched: 10-14 days
  • Immature roots: 4-6 weeks
  • Mature roots: 7-9 months
  • Fresh-cut (Lightly processed): 3-4 weeks

Common storage conditions rarely achieve the optimum temperature for long- term storage to prevent decay, sprouting, and wilting. At storage temperatures of 3-5°C, mature carrots can be stored with minimal decay for 3-5 months.

Common ‘Cello-pack' carrots are typically immature and may be stored successfully for 2-3 weeks at 3-5°C. Bunched carrots are highly perishable due to the presence of the shoots (tops). Good quality is generally maintained only for 8-12 days, even with contact ice.

Lighlty processed (fresh-cut, cut and peel) carrots typically maintain quality of 2-3 weeks at 3-5°C.

Optimum Relative Humidity

98-100%

High relative humidity is essential to prevent dessication and loss of crispness. Free moisture from the washing process or unevaporated condensation, common with plastic bin-liners (and due to fluctuating temperatures) will promote decay.

Rates of Respiration

Temperature ml CO2/kg·hr
°C (°F) Topped Bunched
0 (32) 5-10 9-18
5 (41) 7-13 13-25
10 (50) 10-21 16-31
15 (59) 13-27 28-53
20 (68) 23-48 44-60
25 (77) NA NA

To calculate heat production multiply ml CO2/kg·hr by 440 to get Btu/ton/day or by 122 to get kcal/metric ton/day.
NA= Not applicable.

Rates of Ethylene Production

>0.1 µl/kg·hr at 20°C (68°F)

Responses to Ethylene

Exposure to ethylene will induce the development of bitter flavor due to isocoumarin formation. Exposure to as little as 0.5ppm exogenous ethylene will result in perceptible bitter flavor, within 2 weeks, at normal storage conditions. Thus, carrots should not be mixed with ethylene-producing commodities.

Responses to Controlled Atmospheres (CA)

Controlled atmosphere is of limited use for carrots and does not extend postharvest life of carrots beyond that in air. CO2 concentrations above 5% have been shown to increase spoilage. Low oxygen concentrations, below 3%, are not well tolerated and generally results in increased bacterial rot.

Disorders

Physiological and Physical Disorders

Intact Roots. Bruising, shatter-cracks and tip-breakage are signs of  rough handling. Nantes-type carrots are particularly susceptible. Sprouting will continue as carrot roots develop new shoots after harvest. This is one reason low temperature postharvest management is critical. Common associated disorders include wilting, shriveling, or rubberiness due to dessication. White Root is a physiologic disorder due to suboptimal production conditions which results in patchy or streaks of low color on the carrot roots.

Intact or Fresh-cut. Bitterness may be caused by preharvest stress (improper irrigation scheduling) or exposure to ethylene from ripening rooms or mixing with commodities such as apples. Freezing injury will likely result at temperatures of -1.2°C ( 29.5°F) or lower. Frozen carrots generally exhibit an outer ring of water-soaked tissue, viewed in cross section, which blackens in 2-3 days.

Fresh-cut. White Blush, due to dehydration of cut or abrasion-peeled surfaces, has been a problem on fresh-cut carrots. Sharp cutting blades and residual free-moisture on the surface of the processed carrots will significantly delay the development of the disorder.

Pathological Disorders

The most prominent postharvest disease concerns are Gray Mold (Botrytis rot) Watery Rot (Sclerotinia rot), Rhizopus rot, Bacterial Soft Rot, induced by Erwinia carotovora subsp. carotovora and Sour Rot (Geotrichum rot). Proper handling and low temperature storage and transportation conditions are the best methods to minimize losses.

Special Considerations

Rapid hydrocooling soon after harvest is strongly recommended.

Disorders Photos

Title: Bacterial Soft Rot (2)

Photo Credit: Don Edwards, UC Davis 

Title: Black Mold

Photo Credit: Don Edwards, UC Davis 

Title: Crater Rot

Photo Credit: Don Edwards, UC Davis 

Title: Gray Mold Rot

Photo Credit: Don Edwards, UC Davis 

Title: Pitting

Photo Credit: Marita Cantwell, UC Davis  

Title: White Rot

Photo Credit: Don Edwards, UC Davis 

Title: Bacterial Soft Rot (1)

Photo Credit: Marita Cantwell, UC Davis  

Date

June 2002

Cauliflower

Recommendations for Maintaining Postharvest Quality

cauliflower007
Trevor V. Suslow and Marita Cantwell

Department of Plant Sciences, University of California, Davis

Cauliflower PDF

Maturity & Quality

Maturity Indices

Cauliflowers are selected for size and compactness of the head or curd. Mature curds are at least 15 cm (6 inches) in diameter. Loose or protruding floral parts, creating a ‘ricy’ appearance, are a sign of overmaturity. Cauliflower is packaged after being closely trimmed into single layer cartons of 12 to 24 heads, with 12’s most common.

Cauliflower is primarily marketed with closely trimmed leaves and overwrapped with perforated film. Overwraps should provide four to six 1/4-inch holes per head to allow adequate ventilation.

Quality Indices

A firm and compact head of white to cream white curds surrounded by a crown of well-trimmed, turgid green leaves. Additional quality indices are size, freedom from severe yellowing due to sunlight exposure, freedom from handling defects and decay, and an absence of ‘riciness’.

U.S. grade No. 1

Maturity & Quality Photos

Title: Green Cauliflower

Photo Credit: Adel Kader, UC Davis  

Temperature & Controlled Atmosphere

Optimum Temperature

0°C (32°F)

Storage of cauliflower is generally not recommended for more than 3 weeks for good visual and sensory quality. Wilting, browning, yellowing of leaves, and decay are likely to increase following storage beyond 3-4 weeks or at higher than recommended storage temperatures.

Optimum Relative Humidity

95-98%

Rates of Respiration

Temperature °C Temperature °F ml CO2/kg·hr
0 32 8-9
5 41 10-11
10 50 16-18
15 59 21-25
20 68 37-42
25 77 43-48

To calculate heat production, multiply ml CO2/kg·hr by 440 to get BTU/ton/day or by 122 to get kcal/metric ton /day.

Rates of Ethylene Production


Responses to Ethylene

Cauliflower is highly sensitive to exogenous ethylene. Discoloration of the curd and  accelerated yellowing and detachment of wrapper leaf stalks will result from low levels of ethylene during distribution and short-term storage. Do not mix loads such as apples, melons and tomatoes with cauliflower.

Responses to Controlled Atmosphere (CA)

Controlled or modified atmospheres offer moderate to little benefit to cauliflower. Injury from low O2 (<2%) or elevated CO2 (>5%) may not be visual and will only be evident after cooking. When the curds become grayish, extremely soft, and emit strong off-odor. Higher levels (>10%) of CO2 will induce this injury within 48 hours. Combined low O2 and slightly elevated CO2 levels (3-5%) delay leaf yellowing and the onset of curd browning by a few days.

Temperature & Controlled Atmosphere Photos

Title: Discoloration

Photo Credit: Marita Cantwell, UC Davis

Title: Ethylene Effects (1)

Photo Credit: Yilmaz Ilker, Postharvest Consultant, New Jersey 

Title: Ethylene Effects (2)

Photo Credit: Don Edwards, University of California, Davis

Disorders

Physiological and Physical Disorders

Freezing Injury. Freezing injury will be initiated at -0.8°C (30.6°F). Symptoms of  freezing injury include a watersoaked and greyish curd and watersoaked or wilted crown leaves. The curd will become brown and gelatinous in appearance following invasion by soft-rot bacteria.

Harvesting should be done with great care to prevent damage to the highly sensitive turgid curds. Cauliflower should never be handled by the curd portion of the head. Cauliflower should never be allowed to roll or scuff across a harvest -conveyor belt, table, or other work surface. Bruising is very common and leads to rapid browning and decay when attention to careful harvest and handling practices are not followed.

Pathological Disorders

Diseases are an important source of postharvest loss, particularly in combination  with rough handling and poor temperature control. A large list of bacterial and fungal pathogens cause postharvest losses in transit, storage, and to the consumer. Bacterial Soft-Rot (primarily Erwinia and Pseudomonas), Black Spot (Alternaria alternata.), Grey Mold (Botrytis cinerea), and Cladosporium Rot are common disorders.

Special Considerations

For fresh-cut applications, the sensitivity of cauliflower to improper modified atmosphere (See Responses to CA) demands very careful selection of packaging films and proper temperature management.

Disorders Photos

Title: Decay Rating Scale

Photo Credit: Marita Cantwell, UC Davis 

Title: Leaf Abscission caused by Ethylene

Photo Credit: Don Edwards, UC Davis  

Title: Mechanical Damage (1)

Photo Credit: Adel Kader, UC Davis  

Title: Mechanical Damage (2)

Photo Credit: Adel Kader, UC Davis  

Title: Solar Yellowing

Photo Credit: Adel Kader, UC Davis

Date

February 1998

Celery

Recommendations for Maintaining Postharvest Quality

celery073
Trevor Suslow and Marita Cantwell

Department of Plant Sciences, University of California, Davis

Maturity & Quality

Maturity Indices

Celery is harvested when the overall field reaches the desired marketable size and before the outer petioles develop "pithiness" (see Pith Breakdown below). Celery has very uniform crop growth and fields are harvested only once and stalks are packed by size after trimming outer petioles and leaves.

Quality Indices

High quality celery consists of stalks which are well formed, have thick petioles, are compact (not significantly bowed or bulging), have minimal petiole twisting, and have a light green and fresh appearance. Additional quality indices are stalk and midrib length, freedom from defects such as blackheart, pithy petioles, seedstalks, cracks or splits, and freedom from insect damage and decay.

U.S. Grades: Extra No. 1; No. 1; No. 2 (Grade Standards established 1957)
Celery may be sold as "Unclassified" to designate a lot which has not been graded within U.S. standards.

Temperature & Controlled Atmosphere

Optimum Temperature

0°C (32°F)

At optimum conditions, celery should have good quality after storage up to 5 to 7 weeks. Commonly, celery is rapidly pre-cooled and then stored at 0 to 2°C (32 to 36°F). If storage is intended to be less than one month, storing celery at 5°C (41°F) is not recommended for more than 2 weeks in order to maintain good visual and sensory quality. Some continued growth of inner stalks will occur postharvest at temperatures >0°C (32°F).

Optimum Relative Humidity

98-100% R.H.

Rates of Respiration

Temperature ml CO2/kg·hr
0°C (32°F) 3
5°C (41°F) 5
10°C (50°F) 12
15°C (59°F) 17
20°C (68°F) 32

To calculate heat production multiply ml CO2/kg·hr by 440 to get Btu/ton/day or by 122 to get kcal/metric ton/day.

Rates of Ethylene Production


Responses to Ethylene

Celery is not very sensitive to exogenous ethylene at low levels and low temperatures. Loss of green color can result from exposure to 10 ppm or higher ethylene concentrations at above 5°C (41°F).

Responses to Controlled Atmospheres (CA)

Controlled or modified atmospheres offer moderate benefit to celery. Delayed senescence and decay development have been observed at 2-4% O2 and 3-5% CO2.

Injury from low O2 (<2%) or elevated CO2 (≥10%) will induce off-odors, off-flavors, and internal leaf browning. CA for mixed storage or long distance transport of celery and lettuce has some commercial application. Elevated CO2 levels delay leaf yellowing and decay but could not be used in mixed loads with lettuce (lettuce does not tolerate CO2 enriched atmosphere).

Disorders

Physiological and Physical Disorders

Blackheart. Internal leaves develop a brown discoloration which eventually becomes deep black. The cause is similar to tip-burn of lettuce or blossom-end rot of tomato. Although many predisposing factors may be involved, water-stress results in a calcium deficiency disorder causing cell death.

Brown Checking. Splits, primarily along the inner surface of the petioles result from boron deficiency.

Freezing Injury. Freezing injury will be initiated at -0.5°C (31.1°F). Symptoms of freezing injury include a watersoaked appearance on thawing and wilted leaves. Mild freezing causes pitting or short streaks in the petiole which develop a brown discoloration with additional storage.

Pith Breakdown. The breakdown of the internal tissue of the petiole, the pith, is often refereed to as "pithiness" or pithy stems. The aerenchyma tissue of the petiole becomes white, spongy or vacuolated, and appears dry. Pith breakdown is induced by several factors that result in the induction of senescence, including cold stress, water stress, pre-bolting changes (seed stalk induction), and root infections. Pith breakdown will develop after harvest, but slowly under proper storage conditions.

Crushing or cracking. Common and leads to rapid browning and decay. Harvesting, packing and handling should be done with great care to prevent damage to the highly sensitive turgid petioles.

Pathological Disorders

Diseases are an important source of postharvest loss, particularly in combination with rough handling and poor temperature control. The major bacterial and fungal pathogens that cause postharvest losses in transit, storage, and to the consumer are Bacterial Soft-Rot (primarily Erwinia and Pseudomonas), Gray Mold (Botrytis cinerea), and Watery Rot (Sclerotinia spp.). Botrytis and Sclerotinia will develop over a period of a few weeks, even at 2°C (35.6°F).

Special Considerations

Cut petioles of celery, as for fresh-cut, are very prone to bacterial decay. Less decay and greatly delayed decay symptoms will result from the use of sharp blades, minimizing abrasions or other damage to cut-ends during packaging, and good sanitation.

Disorders Photos

Title: Bacterial Soft Rot (1)

Photo Credit: Don Edwards, UC Davis

Title: Bacterial Soft Rot (2)

Photo Credit: Don Edwards, UC Davis

Title: Freezing Damage (1)

Photo Credit: Don Edwards, UC Davis

Title: Freezing Damage (2)

Photo Credit: Don Edwards, UC Davis

Title: Pink Rot

Photo Credit: Don Edwards, UC Davis

Date

May 1998

Chile Pepper

Recommendations for Maintaining Postharvest Quality

chile pepper010
Marita Cantwell

Department of Plant Sciences, University of California, Davis

Maturity & Quality

Introduction

Chile peppers are a diverse group and come from one of 3 species of the genus Capsicum: C. annuum (most chile peppers), C. frutescens (Tabasco), and C. chinense (Habanero).

Maturity Indices

Mature-Green Chiles: fruit size, firmness, color
Colored Chiles: minimum 50% coloration to achieve complete color development

Quality Indices

  • Uniform shape, size and color typical of variety
  • Firmness
  • Freedom from defects such as cracks, decay, sunburn

Maturity & Quality Photos

Title: Internal maturity

Photo Credit: Marita Cantwell, UC Davis

Title: Maturity and ripeness

Photo Credit: Adel Kader, UC Davis

Temperature & Controlled Atmosphere

Optimum Temperature

Chiles should be cooled as soon as possible to reduce water loss. Chile peppers are not as chilling sensitive as bell peppers. Chile peppers stored above 7.5°C (45°F) suffer more water loss, shrivel, color change and decay. Storage at 7.5°C (45°F) is considered the best for maximum shelf-life (3-5 weeks). Chiles can be stored at 5°C (41°F) for at least 2 weeks without visible signs of chilling injury. Storage at 5°C reduces water loss and shrivel, but after 2-3 weeks, chilling injury is mostly detected as discoloration of the seeds. Symptoms of chilling injury include pitting, decay, discoloration of the seed cavity, and excessive softening. Ripe or colored chiles are less chilling sensitive than mature-green chiles.

Optimum Relative Humidity

>95%; the firmness of chile peppers is directly related to water loss during storage.

Rates of Respiration

Temperature ml CO2/kg·hr
10°C (50°F) 5-10
20°C (68°F) 20-30
27°C (81°F) 40-80

To calculate heat production multiply ml CO2/kg•hr by 440 to get BTU/ton/ day or by 122 to get kcal/metric ton/day.

Respiration rates of chile peppers vary considerably depending on the specific type or cultivar. Jalapeno chiles have lower respiration rates while Tabasco and Chiltepin have very high respiration rates (higher than those indicated above).

Rates of Ethylene Production

Some chiles such as jalapeños show a nonclimacteric physiology during color change and produce very low levels of ethylene: 0.1-0.2 µl/kg•hr at 20-25°C (68-77°F). Other chiles such as Habaneros show increases in ethylene production during ripening and may produce over 1 µl/kg•hr at 20-25°C (68-77°F).

Responses to Ethylene

Responses to ethylene depend on the particular variety of chile. Chile poblanos for example may respond to ethylene treatment, while Jalapeño peppers do not. As with bell peppers, holding partially colored chile peppers at warmer temperatures of 20-25°C (68-77°F) with high humidity (>95%) is effective to complete color development. Adding ethylene may further enhance ripening but response is variety dependent.

Responses to Controlled Atmospheres (CA)

At recommended storage temperature (7-8°C), controlled and modified atmospheres of 3-5% O2 in combination with 0-5% CO2 are considered to provide only slight benefit to chile peppers. Low O2 atmospheres may retard color development. High CO2 atmospheres (>5%) can damage mature-green chiles (pitting, discoloration, softening), while colored (fully ripe) chiles are more tolerant of CO2.

Temperature & Controlled Atmosphere Photos

Title: Chilling injury-Caribe

Photo Credit: Marita Cantwell, UC Davis

Title: Chilling injury-Habanero

Photo Credit: Marita Cantwell, UC Davis

Title: Chilling injury-Serrano

Photo Credit: Marita Cantwell, UC Davis

Disorders

Physiological Disorders

Blossom end rot. This disorder occurs as a slight discoloration or a severe dark sunken lesion at or near the blossom end; it is caused by temporary insufficiencies of calcium due to water stress and may occur under high temperature conditions when the peppers are rapidly growing.

Chilling injury. Symptoms of chilling injury include surface pitting, water-soaked areas, decay (especially Alternaria), and discoloration of the seed cavity.

Pathological Disorders

Common decay causing organisms are Botrytis, Alternaria, and soft rots of fungal and bacterial origin.

Botrytis or Grey mold. A common decay-causing organism on chile peppers; field sanitation and prevention of wounds on the fruit help reduce its incidence. Botrytis will grow well at the recommended storage temperatures. Hot water dips of peppers can effectively control botrytis rot (55°C [130°F] water for 4 minutes) without causing fruit injury.

Bacterial Soft Rot. Soft rotting areas can be caused by several bacteria which attack damaged tissue; soft rots can also be common on washed or hydrocooled chile peppers where water sanitation was deficient.

Other Common Postharvest Defects

Mechanical damage (crushing, stem punctures, scrapes, etc.) is common on chile peppers; physical injury not only detracts from the visual quality of the chiles but also causes increased weight loss and decay.

Special Considerations

The pungency or hotness of chile peppers is due to capsaicinoids (capsaicin is the main one) and hotness varies depending on the cultivar or genetics of the chile peppers. Environmental factors and maturity of the chiles also affects the capsaicin concentrations. Chiles that are stored under a range of temperatures and are still of marketable quality maintain their capsaicin concentrations.
For U.S. markets, corking (corky striations on the fruit surface) is considered unattractive. However in other markets, corking is a recognized characteristic of certain cultivars and is usually associated with jalapeño chiles that are prepared in oil and vinegar as a side dish.

[For more information, see our publication “ Fruit Ripening & Ethylene Management ”, available for purchase using our Publication order form .]

Disorders Photos

Title: Bacterial decay

Photo Credit: Marita Cantwell, UC Davis

Title: Defects-1

Photo Credit: Marita Cantwell, UC Davis

Title: Defects-2

Photo Credit: Marita Cantwell, UC Davis

Title: Fungal decay

Photo Credit: Marita Cantwell, UC Davis

Date

February 2009

Corn, Sweet

Recommendations for Maintaining Postharvest Quality

corn074
Trevor V. Suslow and Marita Cantwell

Department of Plant Sciences, University of California, Davis

Maturity & Quality

General Information

Sweet corn postharvest expectations have changed dramatically with the increased availability and popularity of super sweet varieties based on the shrunken-2 gene (sh-2) and other naturally-occurring sweetness enhancing mutations. Although there is no relation to sweetness, regional consumer perceptions and preferences for kernel color have also caused significant shifts from traditional yellow corn to white and bicolor corn.

Maturity Indices

Sweet corn is considered mature for fresh market consumption or "baby kernel" processing when the pollination silks are dried and the kernels are still immature. The husk leaves remain tight and have a good green appearance. The ear is firm and turgid. The kernels are plump and appear 'milky', and not doughy, when squeezed. At this point the kernels of standard 'sugary' corn are 70-75% water content and kernels of sh-2 corn are at 77-78% water content.

Quality Indices

Quality of fresh market sweet corn is judged by its fresh, uniform appearance, uniform and well filled rows, plumpness of kernels, milky kernel contents, and freedom from damage and defects (discoloration, harvest injury, worm damage, live insects, decaying silks or kernels). Trimmed, husked, or minimally processed whole-ears (i.e. microwave consumer packs) have additional grade standards for husk cover, husk appearance, length, and other quality indicators.

U.S. Grades are Fancy, Fancy-Husked, No. 1, No. 1-Husked, and No. 2 (effective Feb. 12, 1992)

Temperature & Controlled Atmosphere

Optimum Temperature

0°C-1.5°C (32°F-34°F)

Typically iced. Standard sweet corn is not stored for more than a few days due to the rapid deterioration of quality, even at ideal temperatures. When short-term storage is necessary for orderly marketing, the maximum duration including transit times should not exceed 7 days. Super sweet corn has been stored at 0°C for up to 21 days with generally acceptable market quality.

Relative Humidity

95-98%

Cooling and Top Icing

Rapid removal of field heat and continuous and proper refrigeration are essential to the maintenance of sweet corn quality. Sweet corn is generally hydrocooled and packed with ice and/or top-iced. After thorough cooling and icing, storage and transit temperatures are held slightly above 0°C (32°F) to prevent freezing of the ice layer and "capping-off" of the container, which could reduce proper air circulation. Handling in bulk containers should be avoided unless provisions for generous and uniform icing can be assured.

Rates of Respiration

Temperature 
°C (°F)
ml CO2/kg·hr
0 (32) 30-51
5 (41) 43-83
10 (50) 104-120
15 (59) 151-175
20 (68) 268-311
25 (77) 282-435

To calculate heat production multiply ml CO2/kg·hr by 440 to get Btu/ton/day or by 122 to get kcal/metric ton/day.

Rates of Ethylene Production


Responses to Ethylene

Exogenous ethylene is not considered an important postharvest handling factor.

Responses to Controlled Atmospheres

Controlled or modified atmosphere storage or shipping offer moderate benefits to sweet corn quality maintenance. Low O2 levels (3%) and elevated CO2 (10%) delay loss of sucrose content and maintain appearance of husks. CA at 5°C (41°F) is superior to storage in air alone, but sugar content is not retain-ed as well as corn stored at 0°C (32°F). Sweet corn does not tolerate low 2 (<2%) or elevated CO2 (greater than or equal to 20%).

Disorders

Physiological and Physical Disorders

Freezing Injury. Freezing injury will be initiated at -0.6°C (31°F). Symptoms of freezing injury include watersoaked patches on the husks and watersoaked kernels becoming gelatinous and developing off-odors over time.

Fresh market harvesting should be done by hand. Ears are snapped downward and away from the main stalk. Stalk ends are trimmed short to prevent excessive moisture loss.

Pathological Disorders

Diseases are not an important source of postharvest loss as compared to field acquired insect damage and physiological deterioration due to the high rate of respiration and conversion of sugars to starch. Dry silks often develop superficial molds after longer storage (greater than 10 days).

Special Considerations

Minimally processed frozen sweet corn may have better quality when the super sweet (sh-2) genotype is used rather than the typical sweet (su) genotype. Blanching prior to freezing is a common commercial and home consumer practice that may be minimized for super sweet varieties due to lower activity of enzymes which cause flavor changes. UC Davis research has shown that super sweet varieties typically require a 4 min blanch while sweet corn varieties require 6 or more minutes for corn-on-the-cob. Research done by both the USDA and UC Davis shows that during frozen storage of super sweet corn, sucrose increased and reducing sugars decreased in unblanched super sweet corn. After frozen storage for 8-9 months, sensory panels preferred blanched rather than unblanched super sweet corn.

Disorders Photos

Title: Freezing Damage

Photo Credit: Marita Cantwell, UC Davis

Date

August 1997

Cucumber

Recommendations for Maintaining Postharvest Quality

cucumber011
Trevor V. Suslow and Marita Cantwell

Department of Plant Sciences, University of California, Davis

Maturity & Quality

Maturity Indices

Cucumbers are harvested at a range of developmental stages. Depending on cultivar and temperature, the time from flowering to harvest may be 55 to 60 days. Generally fruit are harvested at a slightly immature stage, near full size but before seeds fully enlarge and harden. Firmness and external glossiness are also indicators of a pre-maturity condition. At proper harvest maturity, a jellylike material has begun to form in the seed cavity.

Quality Indices

Table or slicing cucumber quality is primarily based on uniform shape, firmness and a dark green skin color. Additional quality indices are size, freedom from growth or handling defects, freedom from decay, and an absence of yellowing.

U.S. grades are Fancy, Extra 1, No. 1, No. 1 Small, No. 1 Large and No. 2.

Industry grades and specifications follow the packing conventions SuperSelect, Select, Small Super, Small, Large, and Plain. These terms have no enforceable contractual value.

Maturity & Quality Photos

Title: Color Rating Scales

Photo Credit: Adel Kader, UC Davis

Title: USDA Color

Photo Credit: Adel Kader, UC Davis

Temperature & Controlled Atmosphere

Optimum Temperature

10-12.5°C (50-55°F)

Storage of cucumber is generally less than 14 days as visual and sensory quality deteriorate rapidly. Shriveling, yellowing, and decay are likely to increase following storage beyond two weeks, especially after removal to typical retail conditions. Short term storage or transit temperatures below this range (such as 7.2°C (45°F)) are commonly used but will result in chilling injury after 2-3 days.

Chilling Injury. Cucumbers are chilling sensitive at temperatures below 10°C (50°F) if held for more than a day to 3 days depending on temperature and cultivar. Consequences of chilling injury are water-soaked areas, pitting and accelerated decay. Chilling injury is cumulative and may be initiated in the field prior to harvest. Cucumber varieties vary considerably in their susceptibility to chilling injury.

Optimum Relative Humidity

95%

Rates of Respiration

Temperature 10°C (50°F) 15°C (59°F) 20°C (68°F) 25°C (77°F)
ml CO2/kg·hr 12-15 12-17 7-24 10-26

To calculate heat production, multiply ml CO2/kg·hr by 440 to get BTU/ton/day or by 122 to get kcal/metric ton/day.
Respiration varies widely above 10°C due to different stages of maturity. Less mature cucumbers have higher respiration rates.

Rates of Ethylene Production

0.1-1.0 µl/kg·hr at 20°C (68°F)

Responses to Ethylene

Cucumbers are highly sensitive to exogenous ethylene. Accelerated yellowing and decay will result from low levels (1-5 ppm) of ethylene during distribution and short-term storage. Do not mix commodities such as bananas, melons and tomatoes with cucumber.

Responses to Controlled Atmospheres (CA)

Controlled or modified atmosphere storage or shipping offer moderate to little benefit to cucumber quality maintenance. Low O2 levels (3-5%) delay yellowing and the onset of decay by a few days. Cucumber tolerates elevated CO2 up (CA) to 10% but storage life is not extended beyond the benefit of reduced levels of O2.

Temperature & Controlled Atmosphere Photos

Title: Chilling Injury (1)

Photo Credit: Yilmaz Ilker, Postharvest Consultant, New Jersey 

Title: Chilling Injury (2)

Photo Credit: Yilmaz Ilker, Postharvest Consultant, New Jersey 

Title: Chilling Injury (3)

Photo Credit: Don Edwards, UC Davis

Title: Ethylene Damage

Photo Credit: Adel Kader, UC Davis

Disorders

Physiological and Physical Disorders

See Chilling Injury.

Freezing Injury. Freezing injury will be initiated at -0.5°C (31°F). Symptoms of freezing injury include a watersoaked pulp becoming brown and gelatinous in appearance over time.

Harvesting should be done by cutting free of the vine rather than by tearing. "Pulled end" is a quality defect used in establishing grade quality.

Bruising and compression injury are very common when attention to careful harvest and handling practices are not followed.

Pathological Disorders

Diseases are an important source of postharvest loss, particularly in combination with chilling stress. A large list of bacterial and fungal pathogens cause postharvest losses in transit, storage, and to the consumer. Alternaria spp., Didymella Black Rot, Pythium Cottony Leak, and Rhizopus Soft Rot are common disorders.

Special Considerations

Cucumbers are often treated with approved waxes or oils to reduce water loss, reduce abrasion injury and enhance appearance.

Yellowing during the postharvest period is a very common defect. Harvesting fruit at an advanced stage of development, exposure to ethylene, or storage at too high temperature all cause yellowing.

Disorders Photos

Title: Cucumber Defects

Photo Credit: Adel Kader, UC Davis

Title: Fusarium Decay

Photo Credit: Adel Kader, UC Davis

Date

May 1997

Eggplant

Recommendations for Maintaining Postharvest Quality

eggplant076
Marita Cantwell and Trevor V. Suslow

Department of Plant Sciences, University of California, Davis

Maturity & Quality

Maturity Indices

Eggplant fruit are harvested at a range of developmental stages. Depending on cultivar and temperature, the time from flowering to harvest may be 10 to 40 days. Generally fruit are harvested immature before seeds begin to significantly enlarge and harden. Firmness and external glossiness are also indicators of a pre-maturity condition. Eggplant fruit become pithy and bitter as they reach an overmature condition.

Quality Indices

The diversity of eggplant types being marketed has increased greatly in recent years. Standard (American) eggplant quality is primarily based on uniform egg to globular shape, firmness and a dark purple skin color. Additional quality indices are size, freedom from growth or handling defects, freedom from decay, and a fresh green calyx. Other eggplant types include:

  • Japanese - elongated, slender, light to dark purple, very perishable
  • White - small egg shaped to globular, thin skinned
  • Mini-Japanese - small elongate, striated purple and violet
  • Chinese - elongated, slender, light purple

U.S. grades are Fancy, No. 1, and No. 2, and No. 3. Distinction among grades is based solely on size, external appearances, and firmness.

Maturity & Quality Photos

Title: Eggplant Defects

Photo Credit: Marita Cantwell, UC Davis

Temperature & Controlled Atmosphere

Optimum Temperature

10-12°C (50-54°F)

Storage of eggplant is generally less than 14 days as visual and sensory qualities deteriorate rapidly. Decay is likely to increase following storage beyond two weeks, especially after removal to typical retail conditions. Short term storage or transit temperatures below this range are used often to reduce weight loss, but will result in chilling injury after several days.

Chilling Injury. Eggplant fruit are chilling sensitive at temperatures below 10°C (50°F). At 5°C (41°F) chilling injury will occur in 6-8 days. Consequences of chilling injury are pitting, surface bronzing, and browning of seeds and pulp tissue. Accelerated decay by Alternaria spp. is common in chilling stressed fruit. Chilling injury is cumulative and may be initiated in the field prior to harvest.

Days to Visible Chilling Symptoms on each type:

Temperature 0°C (32°F) 2.5°C (36°F) 5°C (41°F) 7.5°C (45°F)
American 1-2 4-5 6-7 12
Japanese - 5-6 8-9 12-14
Chinese 2-3 5-6 10-12 15-16

Optimum Relative Humidity

90-95% R.H.

Rates of Respiration

Temperature 12.5°C (55°F)
ml CO2/kg·hr American 30-39
ml CO2/kg·hr White egg 52-61
ml CO2/kg·hr Japanese 62-69

To calculate heat production, multiply ml CO2/kg·hr by 440 to get BTU/ton/day or by 122 to get kcal/metric ton /day.

Rates of Ethylene Production

0.1-0.7 µl/kg·hr at 12.5°C (55°F)

Responses to Ethylene

Eggplant fruit have a moderate to high sensitivity to exogenous ethylene. Calyx abscission and increased deterioration, particularly browning, may be a problem if eggplants are exposed to >1ppm ethylene during distribution and short-term storage.

Responses to Controlled Atmospheres (CA)

Controlled or modified atmosphere storage or shipping offer little benefit to eggplant quality maintenance. Low O2 levels (3-5%) delay deterioration and the onset of decay by a few days. Eggplant tolerates up to 10% CO2 but storage life is not extended beyond the benefit of reduced levels of O2.

Temperature & Controlled Atmosphere Photos

Title: Chilling Injury (1)

Photo Credit: Marita Cantwell, UC Davis

Title: Chilling Injury (2)

Photo Credit: Marita Cantwell, UC Davis

Title: Chilling Injury (3)

Photo Credit: Marita Cantwell, UC Davis

Title: Chilling Injury Symptoms

Photo Credit: Marita Cantwell, UC Davis

Disorders

Physiological and Physical Disorders

See Chilling injury.

Freezing Injury. Freezing injury will be initiated at -0.8°C (30.6°F), depending on the soluble solids content. Symptoms of freezing injury include a watersoaked pulp becoming brown and desiccated in appearance over time.

Harvesting should be done by cutting the calyx-stem free from the plant rather than by tearing. Cotton gloves are often used.

Bruising and compression injury are very common when attention to careful harvest and handling practices are not followed. Eggplant cannot withstand stacking in bulk containers.

Pathological Disorders

Diseases are an important source of postharvest loss, particularly in combination with chilling stress. Common fungal pathogens are Alternaria (Black Mold Rot), Botrytis (Gray Mold Rot), Rhizopus (Hairy Rot), and Phomopsis Rot.

Special Considerations

Rapid cooling, primarily to reduce water loss, soon after harvest is essential for optimal postharvest keeping quality. The precooling endpoint is typically 10°C (50°F). Forced-air cooling is the most effective practice. Room cooling after washing or hydrocooling is the most common practice. Moistened paper or waxed cartons are often used to reduce water loss. Japanese eggplants lose water 3 times more rapidly than American-type eggplants. Visible signs of water loss are reduction of surface sheen, skin wrinkling, spongy flesh, and browning of the calyx.

Chilling injury and water loss can be reduced by storing of eggplant in polyethylene bags or polymeric film overwraps. Increased decay from Botrytis is a potential risk of this practice.

Disorders Photos

Title: Pitting

Photo Credit: Marita Cantwell, UC Davis

Title: Solar Yellowing

Photo Credit: Marita Cantwell, UC Davis

Title: Sun Scald

Photo Credit: Marita Cantwell, UC Davis

Date

May 1997

Garlic

Recommendations for Maintaining Postharvest Quality

garlic077
Marita Cantwell

Department of Plant Sciences, University of California, Davis

Maturity & Quality

Maturity Indices

Garlic can be harvested at different stages of development for specialty markets, but most garlic is harvested when the bulbs are well mature. Harvest occurs after the tops have fallen and are very dry.

Quality Indices

High quality garlic bulbs are clean, white (or other colors typical of the variety), and well cured (dried neck and outer skins). The cloves should be firm to the touch. Cloves from mature bulbs should have a high dry weight and soluble solids content (>35% in both cases).

Grades include U.S. No. 1 and unclassified, and are based primarily on external appearance and freedom from defects. Minimum diameter for fresh market is about 4 cm (1.5 inches).

Temperature & Controlled Atmosphere

Optimum Temperature

-1°C to 0°C (30°F-32°F). The variety of garlic affects potential storage life, and the recommended conditions for commercial storage depend on the expected storage period. Garlic can be kept in good condition for 1-2 months at ambient temperatures (20°C-30°C [68°F-86°F]) under low relative humidity (<75%). However under these conditions, bulbs will eventually become soft, spongy and shriveled due to water loss. For long-term storage, garlic is best maintained at temperatures of -1°C to 0°C (30°F-32°F) with low relative humidity (60-70%). Good airflow is also necessary to prevent any moisture accumilation. Under these conditions garlic can be stored for more than 9 months.

Garlic will eventually lose dormancy, signaled by internal development of the sprout. This occurs most rapidly at intermediate storage temperatures of 5°C-18°C (41°F-65°F). Garlic odor is easily transferred to other products and should be stored separately. High humidity in the storages will favor mold growth and rooting. Mold growth can also be problematic if the garlic has not been well cured before storing.

Optimum Relative Humidity

60 to 70%

Rates of Respiration

Temperature 0°C (32°F) 5°C (41°F) 10°C (50°F) 15°C (59°F) 20°C (68°F)
ml CO2/kg·hr

Intact bulbs
2-6 4-12 6-18 7-15 7-13
Fresh peeled cloves 12 15-20 35-50 - -

To calculate heat production multiply ml CO2/kg·hr by 440 to get Btu/ton/day or by 122 to get kcal/metric ton/day.

Rates of Ethylene Production

Garlic produces only very low amounts of ethylene (

Responses to Ethylene

Not sensitive to ethylene exposure.

Responses to Controlled Atmospheres(CA)

Atmospheres with high CO2 (5-15%) are beneficial in retarding sprout development and decay during storage at 0-5°C. Low O2 alone (0.5%) did not retard sprout development of 'California Late' garlic stored up to 6 months at 0°C. Atmospheres with 15% CO2 may result in some yellow translucent discoloration occurring on some cloves after about 6 months.

Disorders

Physiological and Physical Disorders

Freeze injury. Due to its high solids content, garlic freezes at temperatures below -1°C (30°F).

Waxy breakdown. A physiological disorder that affects garlic during latter stages of growth and is often associated with periods of high temperature near harvest. Early symptoms are small, light yellow areas in the clove flesh that darken to yellow or amber with time. Finally the clove is translucent, sticky and waxy, but the outer dry skins are not usually affected. Waxy breakdown is commonly found in stored and shipped garlic but rarely in the field. Low oxygen levels and inadequate ventilation during handling and storage may also contribute to development of waxy breakdown.

Pathological Disorders

Penicillium rot. (Pencillium corymbiferum and other spp.) Are common problems in stored garlic. Affected garlic bulbs may show little external evidence until decay is advanced. Affected bulbs are light in weight and the individual cloves are soft and spongy and powdery dry. In an advanced stage of decay, the cloves break down in a green or gray powdery mass. Low humidity in storage retards rot development. Less common storage decay problems include Fusarium basal rot (Fusarium oxysporum cepae) which infects the stem plate and causes shattering of the cloves, dry rot due to Botrytis allii, and bacterial rots (Erwinia spp., Pseudomonas spp.).

Special Considerations

To control sprout development and lengthen the storage period, garlic may be treated with preharvest applications of sprout inhibitors (i.e., maleic hydrazide) or be irradiated after harvest. Outer cloves of bulbs are easily damaged during mechanical harvest and these damaged areas discolor and decay during storage. Therefore high quality garlic for the fresh market is usually harvested manually to avoid mechanical damage.

Curing garlic is the process by which the outer leaf sheaths and neck tissues of the bulb are dried. Warm temperatures, low relative humidity, and good airflow are conditions needed for efficient curing. Under favorable climatic conditions in California, the garlic is usually cured in the field. Curing is essential to obtain maximize storage life and have minimal decay.

Garlic flavor is due to the formation of organosulfur compounds when the main odorless precursor alliin is converted by the enzyme alliinase to allicin and other flavor compounds. This occurs at low rates unless the garlic cloves are crushed or damaged. Alliin content decreases during storage of garlic bulbs, but the effect of time, storage temperatures and atmospheres has not yet been well documented.

Disorders Photos

Title: Black Mold

Photo Credit: Marita Cantwell, UC Davis

Title: Sprout Development

Photo Credit: Marita Cantwell, UC Davis

Date

August 2000

Herbs (Fresh Culinary)

Recommendations for Maintaining Postharvest Quality

herb015
Elizabeth J. Mitcham, Carlos H. Crisosto and Adel A. Kader

Department of Plant Sciences, University of California, Davis

Maturity & Quality

General Information

Fresh culinary herbs are variable in botanical origin and in their postharvest properties. This summary is useful for the following fresh herbs: basil, chervil, chives, cilantro, dill, epazote, mache, marjoram, mint, mitsuba, oregano, parsley, sage, shiso, tarragon and thyme. 

Maturity Indices

Many culinary herbs are harvested as soft or semi-woody leafy stems (dill, oregano, tarragon, basil, mint), and the herb can also include immature or mature flowers. Some herbs are harvested as developing leaves (mache) or intact plants (cilantro, parsley).

Quality Indices

Quality characteristics are largely visual and include appearance of freshness, uniformity of size, form and color, and lack of defects (damaged or yellowed leaves, decay, insect damage, wilting). Characteristic aroma is essential for culinary herb quality, and generally essential oils and aroma decrease during storage.

Maturity & Quality Photos

Title: Cilantro Color Scores & Pigments

Photo Credit: Marita Cantwell, UC Davis

Title: Parsley Color Rating Scale

Photo Credit: Adel Kader, UC Davis

Title: Parsley Color Scores & Pigments

Photo Credit: Marita Cantwell, UC Davis

Temperature & Controlled Atmosphere

Optimum Temperature

For most herbs, storage at 0°C (32°F) is required to optimize quality and storage life. Expected shelf-life is 3 weeks at 0°C (32°F) and 2 weeks at 5°C (41°F). See table for specific data on different fresh herbs. Basil and shiso are chilling sensitive and should be stored above 10°C (50°F). Depending on water loss, a shelf-life of 1 to 2 weeks can be expected for basil and shiso. Herbs may be cooled by hydrocooling before packaging or room cooling after packaging. Some herbs such as cilantro and parsley are iced, and some herbs may be vacuum cooled. Because of the small quantities marketed, water loss can be a serious cause of quality loss, especially in the large-leaved herbs such as basil and cilantro.

Effect of temperature with high humidity on the visual quality of fresh culinary herbs stored for 10 days. Visual quality was scored on a 9 to 1 scale, where 9 = excellent, 7 = good, 5 = fair, 3 = poor, 1 = unuseable. A "+" indicates sensitivity to ethylene when stored at 10°C (50°F).

herb_table

Freezing Injury. Freeze damage in fresh herbs will appear as darkened translucent or water-soaked areas which will deteriorate rapidly after thawing. Freeze damage can occur on dill stored at -0.7°C (30.7°F), on chives at -0.9°C (30.4°F), and on parsley at -1.1°C (30.0°F). 

Relative Humidity

>95%

Rates of Respiration

The respiration rates of fresh culinary herbs vary considerably, but values during the first five days from harvest are:

Temperature 0°C (32°F) 10°C (50°F) 20°C (68°F)
ml CO2/kg·hr 6-20 (average for herbs listed = 13) 25-80 (average for herbs listed = 47) 52-300 (average for herbs listed = 118)

To calculate heat production, multiply ml CO2/kg·hr by 440 to get BTU/ton/day or by 122 to get kcal/metric ton-day.

Rates of Ethylene Production

Ethylene production rates vary among the fresh culinary herbs and are generally higher than rates for leafy green vegetable:

Temperature 0°C (32°F) 10°C (50°F) 20°C (68°F)
µL/kg·hr 0.06-0.22 (average for herbs listed = 0.11) 0.10-0.57 (average for herbs listed = 0.43) 0.36-3.00 (average for herbs listed = 1.25)

Responses to Ethylene

The main symptoms of ethylene exposure are yellowing, epinasty (stem curvature) and leaf abscission. Some herbs (marjoram, mint, parsley, organo) are very sensitive to ethylene exposure, while others (sage, thyme, basil, rosemary) are minimally affected or do not respond at all. As with other products, storage at low temperature reduces the detrimental effects of ethylene, (see table in Optimum Temperature and Relative Humidity.

Responses to Controlled Atmosphere (CA)

Some benefit to shelf-life can be obtained with low O2 (1-5%) and high CO2 (5-15%) atmospheres at moderate temperatures 5-10°C (41-50°F). Low O2 atmospheres will reduce respiration rates and reduce the detrimental effects of ethylene. High CO2 atmospheres maintain green color and reduce decay in many herbs (such as parsley and cilantro), but are not beneficial for basil.

Temperature & Controlled Atmosphere Photos

Title: Chilling Effects on Basil

Photo Credit: Marita Cantwell, UC Davis

Title: Chilling Injury of Basil (Genovese) - Temperature and Time

Photo Credit: Marita Cantwell, UC Davis

Title: Chilling Injury vs Temperature on Basil

Photo Credit: Marita Cantwell, UC Davis

Title: Effect of Ethylene on Mint

Photo Credit: Marita Cantwell, UC Davis

Title: Effect of Ethylene on Mitsuba

Photo Credit: Marita Cantwell, UC Davis

Title: Effects of Ethylene on Parsley

Photo Credit: Marita Cantwell, UC Davis

Title: Gai-lan Stored in Air

Photo Credit: Marita Cantwell, UC Davis

Title: Temperature Effect on Arugula

Photo Credit: Marita Cantwell, UC Davis

Title: Temperature Effect on Chives

Photo Credit: Marita Cantwell, UC Davis

Title: Temperature Effect on Cilantro

Photo Credit: Marita Cantwell, UC Davis

Title: Temperature Effect on Young Dill

Photo Credit: Marita Cantwell, UC Davis

Title: Temperature Effects on Basil

Photo Credit: Marita Cantwell, UC Davis

Disorders

Physiological and Physical Disorders

Chilling Injury. Basil and shiso are the only chilling sensitive fresh culinary herbs. Chilling symptoms include browning of the leaves and growing tip, bronzing of the leaf veins, and loss of the glossy appearance of the leaves. The figure below shows the time need to have visible chilling symptoms when basil is stored at different temperatures.

Chilling Injury Score

Chilling Injury Score. label x-axis Days

Days

Development of chilling injury on sweet Italian basil stored at different temperatures. A score of 3 was considered the limit for commercial acceptability (A score of 0 = no injury, 8 = severe injury). 

Damage to the herb leaves at harvest can lead to discoloration and increased susceptibility to decay. 

Pathological Disorders

Fresh culinary herbs can be attacked by the same bacteria and fungi that infect other leafy green products. Bacterial soft-rots are caused by numerous bacteria species and result in a slimy breakdown of the infected tissue. Soft-rots may follow fungal infections. Trimming older leaves, rapid cooling and low temperature storage reduce development of bacterial soft-rots. Water spraying at retail may favor bacterial growth. Fungal pathogens may also lead to a watery breakdown of herb tissues (watery soft-rot caused by Sclerotinia for example) but are distinguished from bacterial soft-rots by the development of spores. Gray mold rot caused by Botrytis cinerea can occur commonly on basil and shiso. Trimming and low temperatures also reduce the severity of these rots. 

Special Considerations

Because of the importance of the essential oils and aroma to fresh culinary herb quality, it is important to emphasize that visual shelf-life is much longer than useful culinary shelf-life. For example, in cilantro, aroma notably declines after 10 days, although cilantro can be marketable for 21 days under some storage conditions. In basil, storage at chilling temperatures greatly reduces aroma quality.

Disorders Photos

Title: Botrytis Decay on Basil

Photo Credit: Marita Cantwell, UC Davis

Title: Postharvest Defects of Cilantro

Photo Credit: Marita Cantwell, UC Davis

Date

February 2001

Jicama

Recommendations for Maintaining Postharvest Quality

jicama033
Marita Cantwell

Department of Plant Sciences, University of California, Davis

Maturity & Quality

Maturity Indices

Jicama (Pachyrhizus erosus) is a warm season legume root crop. It is also called Yam Bean and is a brown skinned turnip-shaped root eaten raw or cooked. Jicama roots can be harvested at various stages of development. Young tender roots (100-150 g) harvested from green plants are found in specialty markets. Fully mature roots, however, weigh from 250-1500 g. Mature roots are characterized by their size and well-developed periderm as well as their starchy-sweet flavor. To favor hardening of the periderm, plant tops are removed mechanically or irrigation is stopped.

Quality Indices

Good quality jicama roots should be smooth and firm, with uniform shape and size, be free from mechanical damage to the skin, and have a crisp, succulent, white sweet-starchy flesh. There are no U.S. Grades for jicama. In Hawaii, however, two grades are recognized based on size and freedom from defects (dirt, discoloration, growth cracks, roughness, insect damage, mechanical injury).

Temperature & Controlled Atmosphere

Optimum Temperature

The recommended conditions for commercial storage of jicama are to keep roots cool and dry. Jicama roots are very chilling sensitive and roots should be stored at 12.5°C to 15°C (55°F to 59°F) with moderate relative humidity (70-80%). A storage life of 2-4 months can be expected under these conditions, although stem sprouts will develop after about 2 months. Sprout development results in weight loss and especially a loss of juiciness of the pulp. Minimizing mechanical damage to the periderm during harvest will reduce decay incidence during storage.

Optimum Relative Humidity

70-80%

Rates of Respiration

Temperature 0°C
(32°F)
5°C
(41°F)
10°C
(50°F)
12.5°C
(55°F)
20°C
(68°F)
ml CO2/kg·hr
Mature roots 2-4 5-6 5-10 2-4 3-4
Fresh-cut pieces 2-4 4-6 6-10  -  -

At 5°C and 10°C (41°F and 50°F) respiration rates increase during storage; rates decrease during storage at temperatures >10°C (50°F). Less mature roots have higher respiration rates.
To calculate heat production multiply ml CO2/kg·hr by 440 to get Btu/ton/day or by 122 to get kcal/metric ton/day.


Rates of Ethylene Production

Jicama produces only very low amounts of ethylene (

Responses to Ethylene

Jicama is not sensitive to ethylene exposure.

Responses to Controlled Atmospheres (CA)

No information is available on the potential benefits of controlled atmosphere storage of intact jicama roots. Based on work with other root crops it would not be expected to provide a benefit. On fresh-cut jicama pieces, however, modified atmospheres with 5-10% CO2 reduced decay development and discoloration at 5°C (41°F).

Disorders

Physiological and Physical Disorders

Jicama roots are very sensitive to chilling injury at temperatures of 10°C (50°F) or below. Depending on variety and production conditions, roots may develop symptoms of chilling injury in 1 to 3 weeks of storage at 10°C (50°F). No chilling injury is observed on roots stored at 12.5°C (55°F). Decay is the main external symptom of chilling injury, and discoloration and loss of crisp texture are the main internal symptoms. The roots eventually become "rubbery" in texture when severely chilled. Internal discoloration typically occurs from the skin inwards and is more common and more severe in moderately chilled roots (stored at 10°C). At lower temperatures, the pulp will take on a translucent appearance but not necessarily develop brown discoloration; these roots probably also exhibit external decay.

Pathological Disorders

The most common decay organisms found externally on jicama roots are species of Penicillium, Rhizopus, and Cladosporium. Most postharvest decay on jicama is a consequence of mechanical injury and chilling injury.

Disorders Photos

Title: Chilling Injury

Photo Credit: Marita Cantwell, UC Davis

Title: Curing Effects

Photo Credit: Marita Cantwell, UC Davis

Date

August 2000

Lettuce, Crisphead

Recommendations for Maintaining Postharvest Quality

crisphead lettuce004
Marita Cantwell and Trevor Suslow

Department of Plant Sciences, University of California, Davis

Maturity & Quality

Maturity Indices

Maturity is based on head compactness. A compact head which can be compressed with moderate hand pressure is considered ideal maturity. A very loose head is immature and a very firm or hard head is overmature. Heads that are immature and mature have much better flavor than overmature heads and also have fewer postharvest problems.

Quality Indices

After trimming outer wrapper leaves, the leaves should be a bright light green color. Leaves should be crisp and turgid.

Maturity & Quality Photos

Title: Lettuce Maturity (1)

Photo Credit: Adel Kader, UC Davis

Title: Lettuce Maturity (2)

Photo Credit: Adel Kader, UC Davis

Temperature & Controlled Atmosphere

Optimum Temperature

0°C (32°F) is required to optimize lettuce storage life. A shelf-life of 21-28 days can be expected at this temperature and RH. At 5°C (41°F) a shelf-life of 14 days can be expected as long as no ethylene is in the environment. Vacuum cooling is usually used for iceberg lettuce, but forced-air cooling may also be used successfully.

Freezing Injury. Freeze damage can occur in the field and cause separation of the epidermis from the leaf. This weakens the leaf and leads to more rapid bacterial decay. During storage, freeze damage can occur if the lettuce is stored at at <-0.2°C (31.7°F). This appears as darkened translucent or water-soaked areas that will turn slimy and deteriorate rapidly after thawing.

Relative Humidity

>95%

Rates of Respiration

Iceberg lettuce heads have moderate respiration rates:

Temperature 0°C (32°F) 5°C (41°F) 10°C (50°F) 15°C (59°F) 20°C (68°F)
ml CO2/kg·hr 3-8 6-10 11-20 16-23 25-30

To calculate heat of production multiply ml CO2/kg·hr by 440 to get Btu/ton-day or by 122 to get kcal/metric ton-day.

Rates of Ethylene Production

Very low,

Responses to Ethylene

Iceberg lettuce is extremely sensitive to ethylene. Russet spotting (see physiological disorders) is the most common symptom of ethylene exposure.

Responses to Controlled Atmospheres (CA)

Some benefit to shelf-life can be obtained with low O2 atmospheres (1-3%) at temperatures of 0-5°C (32-41°F). Low O2 atmospheres will reduce respiration rates and reduce the detrimental effects of ethylene. Intact heads are not benefited by atmospheres containing CO2 and injury may occur with >2% CO2 (see Physiological Disorders, brown stain). Lettuce cut for salad products, however, is commonly packaged in low O2 (<1%) and high CO2 (10%) atmospheres because these conditions control browning on the cut surfaces. On salad pieces, cut surface browning occurs more rapidly and more extensively than do symptoms of brown stain caused by CO2.

Temperature & Controlled Atmosphere Photos

Title: Brown Stain

Photo Credit: Adel Kader, UC Davis

Title: Brown Stain Under Modified Atmospheres &Ethylene

Photo Credit: Adel Kader, UC Davis

Title: Ethylene-induced Russet Spotting

Photo Credit: Adel Kader, UC Davis

Disorders

Physiological and Physical Disorders

Many disorders have been identified for iceberg lettuce. Some very common and important disorders are the following:

Tipburn. A disorder caused in the field and is related to climactic conditions, cultivar selection and mineral nutrition. Leaves with tipburn are unsightly and the damaged leaf margins are weaker and susceptible to decay.

Russet Spotting. A common disorder due to exposure to low concentrations of ethylene which stimulates the production of phenolic compounds which lead to brown pigments. Russet spots appear as dark brown spots especially on the midribs. Under severe conditions, russet spots are found on the green leaf tissue and throughout the head. The disorder is strictly cosmetic but makes the lettuce unmarketable. Ethylene contamination may occur from propane fork lifts, transport in mixed loads, or storage with ethylene-generating fruits such as apples, pears and peaches.

Brown Stain. The symptoms of this disorder are yellowish-reddish-brown large, depressed spots on the midribs mostly. These may darken or enlarge with time. Brown stain also appears as reddish-brown streaks in some cases. Brown stain is caused by exposure to above 3% CO2 atmospheres, especially at low temperatures.

Pink rib. A disorder in which the midribs take on a pinkish coloration. Overmature heads and high storage temperatures increase the disorder. Ethylene exposure does not increase the disorder and low O2 atmospheres do not control it.

Breakage of the midribs often occurs during field packing and causes increased browning and increased susceptibility to decay.

Pathological Disorders

Bacterial soft-rots are caused by numerous bacteria species and result in a slimy breakdown of the infected tissue. Soft-rots may follow fungal infections. Trimming outer leaves, rapid cooling and low temperature storage reduce development of bacterial soft-rots.

Fungal pathogens. May also lead to a watery breakdown of lettuce (watery soft-rot caused by Sclerotinia or gray mold rot caused by Botrytis cinerea) but are distinguished from bacterial soft-rots by the development of black and gray spores. Trimming and low temperatures also reduce the severity of these rots.

Disorders Photos

Title: Grey Mold

Photo Credit: Adel Kader, UC Davis

Title: Mechanical Damage

Photo Credit: Adel Kader, UC Davis

Title: Pink Rib

Photo Credit: Adel Kader, UC Davis

Title: Russet Spotting

Photo Credit: Adel Kader, UC Davis

Title: Rusty Brown Discoloration

Photo Credit: Adel Kader, UC Davis

Title: Severe Symptoms of Russet Spotting

Photo Credit: Adel Kader, UC Davis

Date

June 2002

Lettuce, Romaine

Recommendations for Maintaining Postharvest Quality

romaine lettuce079
Marita Cantwell and Trevor Suslow

Department of Plant Sciences, University of California, Davis

Maturity & Quality

Maturity Indices

Romaine or cos lettuce is an elongated heading lettuce type. Maturity is based on the number of leaves and head development. A very loose or easily compressible head is immature and a very firm or hard head is overmature. Heads that are immature (

Quality Indices

After trimming outer leaves, the leaves should be a bright to dark green color (tinged with red in the red romaine cultivars) with the inner leaves of the head being yellow or light green. The bright to dark green of romaine leaves is indicative of higher vitamin A and vitamin C contents relative to iceberg lettuce types. Leaves should be crisp and turgid, and free from insects, decay or mechanical damage (U.S. Grade No. 1). Different romaine varieties may vary in sweetness and bitterness.

Temperature & Controlled Atmosphere

Optimum Temperature

0°C (32°F) is required to optimize the postharvest life of romaine lettuce. A shelf-life of around 21 days is expected at this temperature. At 5°C (41°F) a shelf-life of about 14 days can be expected as long as no ethylene is in the environment. Water spray-vacuum cooling or hydrocooling are often used for romaine lettuce, but forced-air cooling may also be used.

Freezing Injury. Freeze damage can occur in the field and cause separation of the epidermis from the leaf. This weakens the leaf and leads to bacterial decay during storage. Freeze damage can occur during storage if the lettuce is held at <-0.2°C (31.7°F). This appears as darkened translucent or water-soaked areas that will turn slimy and deteriorate rapidly after thawing.

Relative Humidity

>95%

Rates of Respiration

Romaine lettuce heads have moderate respiration rates, but they are generally higher than rates for iceberg lettuce:

Temperature 5°C (41°F) 10°C (50°F) 15°C (59°F) 20°C (68°F)
ml CO2/kg·hr 9-12 15-20 19-25 30-38

To calculate heat production multiply mL CO2/kg·hr by 440 to get Btu/ton/day or by 122 to get kcal/metric ton/day.

Rates of Ethylene Production

Ethylene production rates are very low:

Responses to Ethylene

Romaine lettuce is sensitive to ethylene. Ethylene damage appears as discolored spots on the midrib. These are generally larger and less defined than those found with ethylene-induced Russet spotting on iceberg lettuce (see physiological disorders). Varieties can vary significantly in their susceptibility to ethylene.

Responses to Controlled Atmospheres (CA)

Some benefit to shelf-life can be obtained with low O2 atmospheres (1-3%) at temperatures of 0-5°C (32-41°F). Low O2 atmospheres will reduce respiration rates and reduce the detrimental effects of ethylene. Intact heads are not generally benefited by atmospheres containing CO2 and injury may occur with >5% CO2 (see physiological disorders, brown stain). Cut Romaine lettuce, however, is commonly packaged in low O2 (<1%) and high CO2 (7-10%) atmospheres because these conditions control browning on the cut surfaces. On salad pieces, cut surface browning occurs more rapidly and more extensively than do symptoms of brown stain caused by CO2. Cut iceberg lettuce tolerates higher CO2 concentrations than cut romaine lettuce.

Temperature & Controlled Atmosphere Photos

Title: Brown Stain

Photo Credit: Adel Kader, UC Davis

Title: Carbon Dioxide Injury (Brown Stain)

Photo Credit: Adel Kader, UC Davis

Disorders

Physiological and Physical Disorders

Several disorders can occur on romaine lettuce. Some very common and important disorders are the following.

Tipburn. A disorder caused in the field and is related to climactic conditions, variety selection and mineral nutrition. Leaves with tipburn are unsightly and the damaged leaf margins are weaker and susceptible to decay.

Ethylene injury. Due to exposure to low concentrations of ethylene gas which stimulates the production of phenolic compounds which in turn leads to brown pigments. Russet spots appear as dark brown spots especially on the midribs. Under severe conditions, russet spots are also found on the green leaf tissue and throughout the head. The disorder is strictly cosmetic but makes the lettuce unmarketable. Ethylene contamination may occur from propane fork lifts, transport in mixed loads, or storage with ethylene-generating fruits such as apples, pears, etc.

Brown Stain. The symptoms of this disorder on romaine lettuce heads are yellowish-reddish-brown large, depressed spots or stains. These are most noticeable on the midribs, and may darken and enlarge with time. Brown stain is caused by exposure to CO2-containing atmospheres, especially at concentrations above 5%. Visual symptoms of brown stain may occur less rapidly on Romaine than on iceberg lettuce.

Pink rib. A disorder associated with heads that are overmature. Higher than recommended storage temperatures can also lead to a increased incidence of pink rib. In this disorder, the midribs take on a generalized pinkish coloration. Ethylene exposure does not appear to affect pink rib and low O2 atmospheres do not control it.

Breakage of the midribs often occurs during field packing, especially on overmature romaine heads, and results in unsightly browning and increased susceptibility to decay. Product harvested early in the morning, when pulp temperatures are lower, is more susceptible to midrib cracking and breakage.

Pathological Disorders

Bacterial soft-rots are caused by numerous bacteria species and result in a slimy breakdown of the infected tissue. Soft-rots may follow fungal infections. Trimming outer leaves, rapid cooling and low temperature storage reduce development of bacterial soft-rots.

Fungal pathogens may also lead to a watery breakdown of lettuce (watery soft-rot caused by Sclerotinia or gray mold rot caused by Botrytis cinerea) but are distinguished from bacterial soft-rots by the development of black and gray spores. Trimming and low temperatures also reduce the severity of these rots.

Special Considerations

Cut or broken midribs of Romaine lettuce may discolor more rapidly than cut pieces of iceberg lettuce. This is probably due to the higher content of phenolic compounds found in romaine leaves compared to iceberg leaves. Romaine varieties can vary greatly in the rate and severity of discoloration of cut pieces.

Date

August 2001

Mushroom

Recommendations for Maintaining Postharvest Quality

mushrooms080
Trevor V. Suslow and Marita Cantwell

Department of Plant Sciences, University of California, Davis

Maturity & Quality

Maturity Indices

Agaricus bisporus mushrooms (Button Mushrooms) are harvested by maturity and not by size. Maturity is reached when the caps are well- rounded and the partial veil is completely intact. The stipe (stalk) should have a small length to thickness ratio. Stipe length should be sufficient to permit some trimming without cutting flush to the veil.

Quality Indices

Good quality, fresh ‘Agaricus' mushrooms should be white to dark brown. White forms are most prevalent. Uniform, well rounded cap with a smooth glossy surface and fully intact veil are indicators of best quality. Stipes are straight and glossy in appearance with an even cut edge. Cleanliness (minimal growth medium residue) and absence of browning or other discoloration are additional quality factors. Visible, open gills and absence of a stipe are negative factors.

U.S. grades are No. 1 and No. 2. Sizes range from Small {Button} (1.9-3.2 cm / .75-1.25 in), Medium (3.2-4.5 cm / 1/25-1.75 in), to Large (4.5 cm / 1.75 in and larger) measured as cap diameter. Grades discriminate for maturity, shape uniformity, cleanliness and trim quality.

Temperature & Controlled Atmosphere

Optimum Temperature

0°C-1.5°C (32°F-35°F) Storage life is typically 5-7 days at 1.5°C (35°F) and 2 days at 4.5°C (40°F).

Optimum Relative Humidity

95-98%

High relative humidity is essential to prevent desiccation and loss of glossiness. Drying is correlated with blackening of the stipe and gills and curling of the cap. Commonly mushrooms are packed and shipped in cartons with a perforated overwrap to maintain high humidity.

Rates of Respiration

Temperature
°C (°F)
ml CO2/kg·hr
0 (32) 14-22
5 (41) 35
10 (50) 50
15 (59) N/A
20 (68) 132-158
25 (77) N/A

To calculate heat production multiply ml CO2/kg·hr by 440 to get Btu/ton/day or by 122 to get kcal/metric ton/day.
NA= not applicable


Rates of Ethylene Production

>0.1 µl/kg·hr at 20°C (68°F)

Responses to Ethylene

Agaricus mushrooms are not significantly impacted by exogenous ethylene.

Responses to Controlled Atmospheres (CA)

Extended storage (~12-15 days) in 3% O2 and 10% CO2 at 0°C has been controlled demonstrated. Elevated CO2 at 10-15% (typically 10%) in air is beneficial in Atmosphere (CA) preventing decay and reducing the rate of blackening of the stipe and gills. The beneficial effect is most pronounced if temperatures cannot be maintained below 5°C (41°F). Short exposure to higher CO2 concentrations (20%) is safe and beneficial only if temperatures can be maintained at 0°C-1°C (32°F-34°F).

Improper control of controlled atmospheres or improper packaging can rapidly lead to depletion of oxygen resulting in conditions favorable for Clostridium botulinum. For this reason, primarily, the use of CA and MA is not common.

Temperature & Controlled Atmosphere Photos

Title: Temperature Effects

Photo Credit: Don Edwards, UC Davis

Disorders

Physiological and Physical Disorders

Mushrooms will continue to develop after harvest which is why low & physical temperature postharvest management is critical. Common disorders include disorders upward bending of caps and opening of the veil.

Mushrooms are easily bruised by rough handling and develop patches of browning discoloration.

Freezing injury. (water-soaked appearance leading to extreme softening) Will likely result at temperatures of -0.6°C (30.9°F) or lower.

CO2 injury. Signs are blackening and pitting.

Pathological Disorders

Disease is generally not an important source of postharvest loss in comparison with physiological senescence and improper handling or bruising. Diseases, such as Bacterial Blotch, and spoilage due to other Pseudomonas spp. are generally eliminated during the harvest or sorting phases although development of patches of decay can occur with elevated temperature or extended storage.

Special Considerations

Rapid forced-air cooling soon after harvest is strongly recommended. Center-loading during shipment promotes good cooling-air circulation necessary for this commodity. Good arrival following surface transportation is enhanced when trailers are equipped with ‘air-shocks' suspension. Agaricus mushrooms are reported to acquire strong odors, such as onion, in mixed loads or short term storage.

Date

June 2002

Nopalitos (Cactus Stems)

Recommendations for Maintaining Postharvest Quality

nopalitos081

Marita Cantwell

Department of Plant Sciences, University of California, Davis

Maturity & Quality

Maturity Indices

Cactus stems or "nopalitos" (in Spanish) are the rapidly-growing succulent stems of the Prickly Pear Cactus (Opuntia spp). They are grown in California as a specialty vegetable or imported from Mexico, where they are a traditional vegetable. Cactus stems are harvested based on size, and can be harvested small (
Quality Indices

Good quality nopalitos are fresh, turgid and a brilliant green color. Nopalitos should be harvested when young and tender and not early in the morning to avoid a high acid content (see special considerations).

Maturity & Quality Photos

Title: Maturity

Photo Credit: Marita Cantwell, UC Davis

Title: Quality (1)

Photo Credit: Marita Cantwell, UC Davis

Title: Quality (2)

Photo Credit: Marita Cantwell, UC Davis

Title: Quality (3)

Photo Credit: Marita Cantwell, UC Davis

Temperature & Controlled Atmosphere

Optimum Temperature

Generally nopalitos should be cooled to about 5°C (41°F) to reduce loss of visual appearance due to water loss. The recommended conditions for storage of nopalitos are 5°C to 10°C (41°F to 50°F) at high relative humidity. The major factors limiting storage life of nopalitos are decay and dehydration. Nopalitos stored under higher temperatures rapidly loss their brilliant shiny appearance, become dull green and may also begin to yellow and curve inward due to water loss. Good quality can be maintained for
Optimum Relative Humidity

90-95%

Rates of Respiration

Temperature 5°C (41°F) 10°C (50°F) 15°C (59°F) 20°C (68°F)
ml CO2/kg·hr 8-10 20-22 28-32 38-44

To calculate heat production multiply ml CO2/kg·hr by 440 to get Btu/ton/day or by 122 to get kcal/metric ton/day.
These are average respiration rates for 10 cm nopalitos; respiration rates of 20cm stems are about 50% lower.

Rates of Ethylene Production

Ethylene production rates are very low (0.05, 0.10 and 0.20 µl/kg·hr at 5°C (41°F), 10°C (50°F) and 20°C (68°F), respectively).

Responses to Ethylene

Nopalitos are not very sensitive to ethylene exposure, but exposure at warmer temperatures will enhance yellowing.

Responses to Controlled Atmospheres (CA)

No information is available on the potential benefits of modified/controlled atmosphere storage of cactus stems. For diced product, moderate CO2 (5-10%) atmospheres may be beneficial.

Disorders

Physiological and Physical Disorders

Chilling injury. Nopalitos are chilling sensitive when stored below 10°C (50°F) . However, 3 weeks at 5°C (41°F) may be needed to observe some chilling symptoms. Chilling damage may be manifested as a superficial bronzing or discoloration and increased susceptibility to decay. The onset of chilling injury will depend on storage temperature, maturity and source of product.

Pathological Disorders

Decay at the cut stem end may be a problem if nopalitos are stored for longer than 2 weeks. Decay is usually avoided by insuring that the nopalitos have not been damaged when cut from the plant. Decay can also occur during storage at places where spines have penetrated the surface.

Special Considerations

Cactus stems should be harvested and handled with care to avoid mechanical damage, especially due to spines from one stem penetrating the neighboring stem. Spine damage leads to a rusty-brown discoloration and pathological problems.

Because of the spines, a cleaned and diced product is an attractive option. The cut nopalitos cannot be washed before marketing because it will cause mucilage to exude and increase discoloration of the cut surfaces. Cleaned and diced nopalitos should be stored between 0°C (32°F) and 5°C (41°F) and have a shelf-life of about 6 days.

Because the prickly pear plant is a CAM plant (Crassulacean Acid Metabolism) and fixes CO2 at night as malic acid before converting it to sugars during the day, the acid content of nopalitos may fluctuate greatly and affect their flavor. Therefore it is recommended to harvest the stems after 2-3 hours of sunlight. Small nopalitos however, are not CAM-active. In addition, low storage temperatures 5°C (41°F) maintain acid levels.

Disorders Photos

Title: Discoloration

Photo Credit: Marita Cantwell, UC Davis

Title: Stem-End Decay

Photo Credit: Marita Cantwell, UC Davis

Date

August 2000

Okra

Recommendations for Maintaining Postharvest Quality

okra082
Marita Cantwell and Trevor Suslow

Department of Plant Sciences, University of California, Davis

Maturity & Quality

Maturity Indices

Okra pods are immature fruits and are harvested when they are very rapidly growing. Harvest typically occurs 3 to 7 days after flowering. Okra should be harvested when the fruit is bright green, the pod is fleshy and seeds are small. After that period, the pod becomes pithy and tough, and the green color and mucilage content decrease.

Quality Indices

Okra pods should be tender and not fibrous, and have a color typical of the cultivar (generally bright green). The pods should be well formed and straight, have a fresh appearance and not show signs of dehydration. Grade is U.S. no. 1. Pods are packed based on length with Fancy, Choice and Jumbo designations for size categories. Okra should be free of defects such as leaves, stems, broken pods, insect damage, and mechanical injury. The tender pods are easily damaged during harvest, especially on the ridges and this leads to unsightly brown and black discoloration. Quality losses that occur during marketing are often associated with mechanical damage, water loss, chilling injury, and decay.

Temperature & Controlled Atmosphere

Optimum Temperature

7-10°C (45-50°F)

Very good quality can be maintained up to 7 to 10 days at these temperatures. If stored at higher temperatures, the pods lose quality due to dehydration, yellowing and decay. When stored at lower than recommended temperatures, chilling injury will be induced (see physiological disorders). Chilling symptoms include surface discoloration, pitting and decay. Okra can be successfully hydrocooled or forced-air cooled.

Optimum Relative Humidity

Weight loss is very high in immature okra pods and cultivars may vary in rate of water loss. A very high relative humidity (95-100%) is needed to retard dehydration, pod toughening, and loss of fresh appearance.

Rates of Respiration

Okra pods have very high respiration rates.

Temperature 5°C (41°F) 10°C (50°F) 15°C (59°F) 20°C (68°F)
ml CO2>/kg·hr 27-30 43-47 69-72 124-137

To calculate heat production multiply ml CO2/kg·hr by 440 to get Btu/ton/day or by 122 to get kcal/metric ton/day.

Rates of Ethylene Production and Responses to Ethlylene

Okra pods have low ethylene production rates (
Responses to Controlled Atmospheres (CA)

Okra is not stored in modified atmospheres commercially. At recommended storage temperatures, CO2 concentrations of 4-10% can help maintain green color and reduce discoloration and decay on damaged pods. CO2 concentrations higher than 10% can lead to off flavors. Low O2 concentrations (3-5%) reduce respiration rates and may also be beneficial.

Disorders

Physiological and Physical Disorders

Chilling injury. The typical symptoms of chilling injury in okra are discoloration, pitting, water-soaked lesions and increased decay (especially after removal to warmer temperatures, as during marketing). Different cultivars may differ in their susceptibility to chilling injury. Calcium dips and modified atmospheres have been reported to reduce chilling symptoms.

Freeze damage. Occurs at temperatures of -1.8°C (28.7°F) or below.

Pathological Disorders

Decay on okra can be due to various common bacterial and fungal organisms, but chilling and injury-enhanced rots are probably the most common causes of loss. Rhizopus, Geotrichum and Rhizoctonia fungal rots as well as bacterial decays due to Pseudomonas sp. have been reported to cause postharvest losses.

Disorders Photos

Title: Chilling Injury 

Photo Credit: Yilmaz Ilker

Date

August 2001

Onions, Dry

Recommendations for Maintaining Postharvest Quality

onion005
Trevor Suslow

Department of Plant Sciences, University of California, Davis

Maturity & Quality

Maturity Indices

  • Indicated when approximately 10 to 20 percent of tops have fallen over
  • Conversion from active growth to dormancy accelerated by undercutting bulbs 1 to 2 inches
  • "Field-dry" maturity is indicated when bulb neck is completely dry to the touch and not slippery. Typically reached at 5-8% weight loss following harvest

Quality Indices

  • Mature neck and scales
  • Firmness
  • Diameter (Bulb size)
  • Absence of decay, insect damage, sunscald, greening, sprouting, freezing injury, bruising, and other defects
  • Degree of pungency
Temperature & Controlled Atmosphere

Optimum Temperature

Curing
Field curing when temperatures are at least 24°C (75°F) or exposure for 12 hrs to 30 to 45°C (86 to 113°F) for forced air-curing

Storage
Mild onions: Typically 0.5 to 1 month at 0°C (32°F)
Pungent Onions: Typically up to 6 to 9 months at 0°C (32°F) depending on the cultivar

Optimum Relative Humidity

Curing
75 to 80% for best scale color development

Storage
65 to 70% with adequate air circulation (1m3/min/m3 of onion)

Rates of Respiration

Whole Onions
3-4 ml/kg·hr at 0-5°C (32-41°F); 27-29 ml/kg·hr at 25-27°C (75-79°F). Storage between 5-25°C (41-75°F) favors sprouting and is not recommended for extended periods.

Diced Onions
40-60 ml/kg·hr at 0-5°C (32-41°F).

To calculate heat production multiply ml CO2/kg·hr by 440 to get BTU/ton/day or by 122 to get kcal/metric ton/day.

Rates of Ethylene Production

Whole Onions

Diced Onions
NA

Responses to Ethylene

Ethylene may encourage sprouting and growth of decay-causing fungi.

Responses to Controlled Atmospheres (CA)

No commercial benefit has been identified for varieties with long storage potential. Onions are damaged by <1% O2 and 10% CO2. There is some commercial use of CA (3% O2 and 5-7% CO2) for sweet onion varieties (short storage potential). Diced onions benefit from CA conditions of 1.5% O2 and 10% CO2.

Disorders

Physiological and Physical Disorders

Freezing Injury. Soft water-soaked scales rapidly decay from subsequent microbial growth.

Translucent Scales. Resembles freezing injury and is prevented by prompt cold storage following curing; 3-4 week delay in cold storage increases risk significantly.

Greening. Exposure to light following curing causes green-coloration of outer scales.

Ammonia Injury. Brown-black blotches result from ammonia gas leakage during storage.


Pathological Disorders

Botrytis Neck Rot. Watery-decay initiates at neck area and moves downward through entire bulb. Light gray to gray fungal growth is generally visible at neck infection and on outer scales. Proper drying and curing of onion essentially prevents this storage disorder. Storage conditions (as above) should be maintained to prevent condensation from forming on the bulbs.

Black Mold. Black discoloration and shriveling at neck and on outer scales caused by the fungus Aspergillus niger. Often associated with bruising and leads to bacterial soft rot. Low temperature storage will delay growth of fungus following field or handling infestation but growth will resume above 15°C (59°F).

Blue Mold. Watery soft rot of neck and outer scales followed by the appearance of green-blue mold (occasionally yellow-green) spores of the fungus Penicillium. Minimize bruising and other mechanical injuries, sunscald, and freezing injury.

Bacterial Rots/Soft Rot. Water-soaked, foul-smelling, viscous liquidy rot caused by Erwinia carotovora subsp. carotovora.

Slippery Skin. Generally visible only at neck area and upon cutting to expose inner scales. Scales have a watery-cooked appearance.

Sour Skin. Slimy, yellow-brown decay generally limited to inner scales which give off a sour odor when exposed.

General Bacterial Rot Control:

  1. Harvest only at full maturity
  2. Proper drying and curing
  3. Minimizing bruising and scraping
  4. Maintaining proper storage conditions (as above) to prevent condensation from forming on the bulbs

Special Considerations

Onions are both storage-odor sources for other commodities, such as apples, celery and pears, and storage-odor absorbers from commodities such as apples.

Disorders Photos

Title: Fusarium Basal Rot

Photo Credit: Don Edwards, UC Davis

Title: Fusarium Bulb Rot

Photo Credit: Don Edwards, UC Davis

Title: Grey Mold

Photo Credit: Don Edwards, UC Davis

Title: Neck Rot

Photo Credit: Don Edwards, UC Davis

Title: Onion Smudge

Photo Credit: Don Edwards, UC Davis

Title: Soft Rot

Photo Credit: Don Edwards, UC Davis

Title: Translucent Scales (1)

Photo Credit: Marita Cantwell, UC Davis

Title: Translucent Scales (2)

Photo Credit: Marita Cantwell, UC Davis

Date

August 1996

Onions, Green Bunch

Recommendations for Maintaining Postharvest Quality

onions green bunch084
Trevor V. Suslow and Marita Cantwell

Department of Plant Sciences, University of California, Davis

Maturity & Quality

Maturity Indices

Maturity of green onions is determined primarily by size which is largely determined by seeding density. Green or "bunching" onions are selected varieties of white onion (Allium cepa) planted at high density or from the non-bulbing onion group (Allium fistulosum) generally called Japanese-bunching. Harvest maturity is generally accepted as mean diameter of 0.6 to 1.3 cm (1/4 to 1/2 inch) in diameter at the base plate of the immature bulb.

Quality Indices

Quality green onions have a thin, white shank or neck at least 5 to 7.5 cm (2-3 inches) in length. Green onions should be well-formed (at most slightly curved or angular), uniform in shape, thin-necked, turgid, bright in color, well cleaned, and free from excessive roots, decay, insect-injury, mechanical damage, broken or crushed leaves, or dehydrated clipped-ends.

U.S. Grade No. 1, No. 2 (Standards established June 1947)

Maturity & Quality Photos

Title: Quality

Photo Credit: Don Edwards, UC Davis

Title: Quality - USDA Color Guides

Photo Credit: Adel Kader, UC Davis

Temperature & Controlled Atmosphere

Optimum Temperature

0°C (32°F)

Green onions held at 32°F will remain fresh and flavorful for up to 4 weeks. Green onions are highly perishable and normally marketed over a short period. Lowering and removing the heat of respiration as well as preventing water loss is critical. Package-icing and perforated polyethylene film liners are used to maintain quality. Typically, storage life of green onions at 10°C (50°F) is 7 to 10 days. Higher temperatures greatly accelerate yellowing and decay of the leaves. Green onions benefit from light misting.

Relative Humidity

>98%

Rates of Respiration

Temperature
°C (°F)
ml CO2/kg·hr
0 (32) 5-16
5 (41) 9-19
10 (50) 18-31
15 (59) 33-58
20 (68) 40-90
25 (77) 49-105


To calculate heat production, multiply ml CO2/kg·hr by 440 to get BTU/ton/day or by 122 to get kcal/metric ton /day.

Rates of Ethylene Production


Responses to Ethylene

Green onions are not sensitive to external ethylene.

Responses to Controlled Atmosphere (CA)

Information varies widely on the optimal conditions and extent of benefit of CA for green onions. In general, a controlled atmosphere of 2% oxygen with 5% carbon dioxide at 0°C (32°F) should allow 6 to 8 weeks storage. Visually, green onions tolerate 1% O2 and 10% CO2 but off-flavors have been associated with extended storage above 5°C (41°F).

Disorders

Physiological and Physical  Disorders

Freezing Injury. Freezing injury will be initiated at -1.0°C (30.6°F). Symptoms of freezing injury include a water-soaked appearance of bulb or leaves and wilted or gelatinous leaves, after thawing. The bulb will become soft or gelatinous in texture in outer tissue. Freeze-injury is rapidly followed by bacterial soft-rot decay.

Curvature. Upward bending of young, elongating shoots will occur in horizontally packed green onions. Prompt cooling and storage at 0°C (32°F) will largely prevent this defect. CA-packaging can further retard curvature (See Responses to CA).

Harvesting, trimming, and banding should be done gently to prevent crushing or other injuries. At harvest, pulling is usually done without undercutting. Bunching is done in the field or in a packing shed. Bruising is common and leads to rapid decay when attention to rapid cooling (within 3 hours of harvest) and cold chain control are not applied.

Pathological Disorders

Diseases may be an important source of postharvest loss in combination with rough handling and poor temperature control. Common diseases are Bacterial Soft-Rot (primarily Erwinia carotovora and Pseudomonas spp) and Grey Mold (Botrytis cinerea). Grey Mold is often associated with barely visible preharvest injury to tender foliage by chemical applications or ozone injury from air pollution.

Special Considerations

Odor. Green onions produce odors that may be adsorbed by many other commodities such as apples, grapes, and mushrooms.

Package-Ice. Used for transportation of green onions has been implicated on several occasions as the cause of outbreaks of food-borne illness due to the pathogens Shigella, Cryptosporidium, and others. Water quality and hygienic handling of ice is essential.

Proper selection of packaging films together with proper temperature management can greatly extend the shelf-quality of green onions trimmed or prepared for bulk ready-to-use format.

Date

November 1998

Peas: Snow and Snap Pod

Recommendations for Maintaining Postharvest Quality

peas085
Trevor V. Suslow and Marita Cantwell

Department of Plant Sciences, University of California, Davis

Maturity & Quality

Introduction

Edible-Pod Peas include both Oriental or Asian (also Snow) flat type pods, harvested when the seeds are very small and immature, and the Snap or Sugar Snap Pea which resemble a typical fresh garden pea but with smaller seeds.

Maturity Indices

Snow Peas are selected for size and maximal recovery of bright green, flat pods with minimal seed enlargement. Older and yellowing pods are avoided by careful hand-harvesting.

Sugar Snap Peas are selected in a similar manner but some degree of seed-pod filling is desirable. Larger seeds rapidly become starchy.

Quality Indices

Edible-pod peas should be uniformly bright green (light to deep green but not yellow-green), fully turgid, clean, and free from damage (Thrip injury, broken pods). The stem and calyxes should be green and there should be very few blossoms attached to the pods.

U.S. Grades: U.S. Fancy, and U.S. No. 1, (established in June 1942)
Standards for Fresh Peas apply to Snap Peas but not Oriental Peas

Temperature & Controlled Atmosphere

Optimum Temperature

0°C (32°F)

Edible-pod peas are highly perishable and will not maintain good quality for more than 2 weeks. Wilting, yellowing of pods, loss of tenderness, development of starchiness and decay are likely to increase following storage beyond 14 days; defects occur faster at common distribution conditions of 5 to 10°C (41 to 50°F).

Relative Humidity

95-98%

Rates of Respiration

Temperature °C Temperature °F ml CO2/kg·hr
0 32 15-24
5 41 27-38
10 50 34-59
15 59 89-101
20 68 123-180

To calculate heat production, multiply ml CO2/kg·hr by 440 to get BTU/ton/day or by 122 to get kcal/metric ton /day.
Respiration rates for edible-pod peas are an approximation based on values for unshelled garden peas; actual values remain to be determined.

Rates of Ethylene Production


Responses to Ethylene

Peas are moderately sensitive to exogenous ethylene. Accelerated yellowing and  decay will result from extended exposure to low levels of ethylene during distribution and short-term storage. The calyx is more sensitive to ethylene than the pod.

Responses to Controlled Atmosphere (CA)

Reports vary widely in the benefit of CA for Sugar and Snap Peas. Atmospheres of 2 to 3% O2 and 2 to 3% CO2 are considered by UC Research to offer the best, but moderate, benefit to peas beyond that of rapid cooling and proper storage. Low O2 may promote off-flavors and off-odors. Other studies report that 5 to 7% CO2 extends pod quality at 0°C.

Disorders

Physiological and Physical Disorders

Freezing. Freezing injury will be initiated at -0.6°C (30.9°F). Freezing injury results in watersoaking typically followed by rapid decay by soft-rot bacteria.

Premature senescence. (Yellowing of pod, browning of calyx, loss of tenderness) will develop rapidly at temperatures 7.5°C (45°F) due to the high rate of respiration.

Harvesting and handling should be done with care to prevent damage to the pods and attached calyx.

Pathological Disorders

A variety of fungal pod-spotting and decay pathogens affect edible-pod peas. Common diseases include Chocolate Spot and Grey mold (Botrytis cinerea), Watery Soft Rot (Sclerotinia sclerotiorum), Rhizopus Rot, and Ascochyta Pod Spot. Bacterial Soft Rot is common following rough handling or freezing injury. Surface decay can occur readily, on weak calyxes (brown at harvest) and on blossom remains.

Special Considerations

Package-icing and top-icing loads may be used for Snow Peas but is typically detrimental to Snap Peas because surface moisture promotes decay. Improper CA/MA conditions in ready-to-cook vegetable medleys often leads to off-flavors and fungal decay (typically Botrytis grey mold) at the blossom-end of the pod.

Disorders Photos

Title: freeze injury

Photo Credit: Marita Cantwell, UC Davis

Title: Grey Mold

Photo Credit: Marita Cantwell, UC Davis

Date

February 1998

Potato, Early Crop

Recommendations for Maintaining Postharvest Quality

potato087
Trevor V. Suslow and Ron Voss

Department of Plant Sciences, University of California, Davis

Maturity & Quality

Maturity Indices

Immature potatoes, generally harvested in spring or early summer, have a thin, poorly developed periderm, or skin. Irrigation and planting bed management, along with the option of vine-killing treatments, manage harvest "maturity". Harvest preparedness generally begins once tubers have reached a desirable size for the variety or market. Immature potatoes are easily bruised and "skinning" leads to shriveling or decays. They are very perishable relative to late-crop potatoes and are only stored for short periods. Curing potatoes for 8 days at 15°C (59°F) and 95% RH will allow extended storage of up to 5 months at 4°C (39°F) and 95 to 98% RH, depending on variety. More typically, early-crop potatoes are harvested, cooled to 15°C (59°F), treated with a sprouting inhibitor, packed and shipped in a short period of time (i.e. 1 to 5 days).

Quality Indices

High quality traits, in commercial trade, include more than 70 to 80% of tubers well shaped, brightness of color (esp. reds, yellows, and whites), uniformity, firmness, freedom from adhering soil, freedom from bruising (black spot or shatter-bruising), scuffing or skinning, growth cracks, sprouting, insect damage, Rhizoctonia Black Scurf, decay, greening, or other defects. Commercial standards in use are typically higher than USDA grade standards. Differentiation of quality for potatoes is very complex.

U.S. Grades: Extra No. 1; No. 1; Commercial; No. 2 (Grade Standards established 1991) Potatoes may be sold as "Unclassified" to designate a lot, which has not been graded within the meaning of U.S. standards.

Maturity & Quality Photos

Title: Quality Defects

Photo Credit: Adel Kader, UC Davis

Title: USDA Potato Greening Color Chart

Photo Credit: Adel Kader, UC Davis

Temperature & Controlled Atmosphere

Optimum Storage Conditions

Intended Use Temperature % RH
Table 7°C (45°F) 98
Frying 10 to 15°C (50-59°F) 95
Chipping 15 to 20°C (59-68°F) 95

At optimum conditions, potatoes should have good quality after storage of 3 to 5 weeks. Storing immature potatoes below 10-13°C (50-55°F) for as few as 3 days may cause the accumulation of reducing sugars leading to excessive browning during frying/chipping. Storage for less than 3 weeks is recommended to maintain good visual and sensory quality of immature potatoes.

Rates of Respiration

Temperature °C Temperature °F ml CO2/kg·hr
5 41 6-8
10 50 7-11
15 59 7-16
20 68 9-23

To calculate heat production, multiply ml CO2/kg·hr by 440 to get BTU/ton/day or by 122 to get kcal/metric ton /day.
Note: Immature potato tubers, which are susceptible to bruising and skinning, can have high respiration rates. Cooler temperatures and/or increased air movement are effective methods to ameliorate. 

Rates of Ethylene Production

Very low; Bruised, cut or otherwise damaged tubers have greatly increased ethylene production rates.

Responses to Ethylene

Potato tubers are not very sensitive to external ethylene. Low levels of external ethylene have been shown to elevate respiration, especially in immature potatoes, and result in weight loss and mild shriveling. After aging for 2-3 months at temperatures above 5°C (41°F) and in the absence of sprouting inhibitor application, low levels of ethylene may retard sprouting. High concentrations of external ethylene may induce sprouting.

Responses to Controlled Atmosphere (CA)

Controlled or modified atmospheres offer little benefit to potato. Periderm development and wound healing is delayed at atmospheres below 5% O2. Injury from low O2 Atmosphere (CA) (<1.5%) or elevated CO2 (>10%) will induce off-odors, off-flavors, internal discoloration, and increased decay.

Temperature & Controlled Atmosphere Photos

Title: Chilling Injury

Photo Credit: Marita Cantwell, UC Davis

Title: Low Oxygen Effects

Photo Credit: Adel Kader, UC Davis

Disorders

Physiological and Physical Disorders

Blackheart. Rare in early-crop potatoes due to typical marketing practices; In conditions of restricted airflow and high respiration, tubers held above 15°C (rapidly above 20°C) develop an internal brown discoloration which eventually becomes deep black. Insufficient oxygen reaches the interior of the tuber under these conditions.

Black Spot. Responsible for significant postharvest losses, particularly in response to over-fertilization with nitrogen, low soil potassium availability, irregular irrigation, and other pre-harvest practices. Non-pigmented compounds form in the vascular bundle tissue just under the skin during storage. Following severe bruising or cutting, the affected tuber tissue turns reddish, then blue becoming black in 24 to 72 hours. Severity increases with time.Varieties differ significantly in their susceptibility and symptom expression.

Chilling Injury. Storage at temperatures near 0°C (32°F) for a few weeks may result in a mahogany discoloration of internal tissue in some varieties. Much longer periods of storage are generally required for chilling injury.

Greening. Exposure to bright light during postharvest handling, or longer periods (1 to 2 weeks) of low light intensity, can result in the development of chlorophyll in the potato tuber, anatomically a modified stem. Associated with greening, bitter and toxic glycoalkaloids, such as solanine, are formed. Solanine also forms in response to bruising, wounding (including fresh processing followed by storage), and during sprouting. Glycoalkaloids are heat stable and minimally impacted by cooking.

Internal Brown Spot. Internal dry, corky reddish-brown or black spots or sectors. Uneven water management and/or widely fluctuating temperatures induce this calcium uptake deficiency, usually early in tuber development. Uneven water availability may also result in Hollow Heart, a corky cavitation at the center of the tuber.

Harvesting, packing and handling should be done with great care to prevent damage to the highly sensitive, thin-skinned, turgid tubers. Crushing, Pressure Bruising, Brown Spot or Shatter Bruising are common defects and may lead to rapid water loss, shriveling and decay.

Brown Spot. Discoloration just beneath the inner surface of the tuber resulting from bruising or rough handling. See Black Spot.

Freezing Injury. Freezing injury will be initiated at -0.8°C (30.5°F). Symptoms of freezing injury include a water-soaked appearance, glassiness, and tissue breakdown on thawing. Mild freezing may also result in chilling injury.

Pathological Disorders

Diseases are an important source of postharvest loss, particularly in combination,with rough handling and poor temperature control. Three major bacterial diseases and a greater number of fungal pathogens are responsible for, occasionally, serious postharvest losses. The major bacterial and fungal pathogens that cause postharvest losses in transit, storage, and to the consumer are Bacterial Soft-Rot (Erwinia carotovora subsp. carotovora and subsp. atroseptica), Ralstonia (ex Pseudomonas, ex Burkholderi) solanacearum,* Phytophthora infestans (late blight), Fusarium Rot (Fusarium spp.), Pink Rot (Phytophthora spp.), and Water rot (Pythium spp.) Occasionally serious diseases of immature tubers include Pink Eye (Pseudomonas fluorescens) and Grey Mold (Botrytis cinerea).

*Not found in California.

Special Considerations

Potatoes may impart an "earthy" odor to apples and pears if held in storage with low air exchange. Potatoes may acquire an off-flavor from odor volatiles released by other produce items.

Disorders Photos

Title: Bacterial Ring Rot

Photo Credit: Don Edwards, UC Davis

Title: Bacterial Soft Rot

Photo Credit: Don Edwards, UC Davis

Title: Black Heart

Photo Credit: Adel Kader, UC Davis

Title: Black Scurf

Photo Credit: Don Edwards, UC Davis

Title: Bruising

Photo Credit: Marita Cantwell, UC Davis

Title: Fusarium Dry Rot

Photo Credit: Don Edwards, UC Davis

Title: Late Blight (1)

Photo Credit: Don Edwards, UC Davis

Title: Late Blight (2)

Photo Credit: Don Edwards, UC Davis

Title: Pink Rot

Photo Credit: Don Edwards, UC Davis

Date

November 1998

Pumpkin & Winter Squash

Recommendations for Maintaining Postharvest Quality

pumpkin088
Marita Cantwell and Trevor V. Suslow

Department of Plant Sciences, University of California, Davis

Maturity & Quality

Maturity Indices

Corking of the stem and subtle changes in rind color (bright green to dull green in ‘Kabocha’ for example, Photo 1, Photo 2) are the main external indications of maturity. Immature fruit have a fleshy stem, maturing fruit will have some stem corking, and well mature fruit will have a well corked stem.  In winter squash, such as butternut, external color changes only slightly during maturation (Photo 3). Internal color should be intense and typical of the cultivar (Photo 4). The concentrations of the yellow and orange carotenoids generally increase only slightly during storage. Maturity at harvest is the major determinant of internal color. Immature fruit will be of inferior eating quality because they contain less stored carbohydrates (Photo 4). Immature fruit will have more decay and weight loss during storage than mature fruits.

Quality Indices

Pumpkin and winter squash should be full sized and well formed with the stem intact. They should be well matured with good rind development typical of the cultivar. Internal quality attributes are high color due to a high carotenoid content, and high dry weight and sugar and starch contents (Photo 4).

Maturity & Quality Photos

Title: Butternut Internal Color Scale

Photo Credit: Marita Cantwell, UC Davis

Title: Butternut Squash External Color Values at 3 harvest stages

Photo Credit: Marita Cantwell, UC Davis

Title: Butternut Squash Internal Color Values at 3 harvest stages

Photo Credit: Marita Cantwell, UC Davis

Title: Kabocha Squash Maturity

Photo Credit: Marita Cantwell, UC Davis

Title: Kabocha Squash Maturity Stages

Photo Credit: Marita Cantwell, UC Davis

Title: Winter Squash Quality

Photo Credit: Adel Kader, UC Davis

Temperature & Controlled Atmosphere

Optimum Temperature

12.5-15°C (55-59°F)

Pumpkins and winter squash are very chilling sensitive when stored below 10°C (50°F). Depending on the cultivar a storage life of 2 to 6 months can be expected at 12.5-15°C (55-59°F). Research at Oregon State University showed that for 8 currently produced winter squash cultivars stored at 10-15°C (50-59°F), 90%, 70% and 50% were marketable after 9, 15 and 20 weeks, respectively. For green rind squashes, storing at 15°C (59°F) may cause degreening, undesirable yellowing, and texture loss. The green rind squashes can be stored at 10-12°C (50-55°F) to prevent degreening, although some chilling injury may occur at the lower temperature. High storage temperature (>15°C) will result in excessive weight loss, color loss and poor eating quality. In a UC Davis study, the best temperature for butternut squash storage for 7 months was 15°C (59°F) (Photo 5).  Besides weight loss and browning and drying of damage areas, higher storage temperatures also lead to more rapid breakdown of pulp tissue (Photo 6).

Optimum Relative Humidity

50-70% with 60% usually considered optimum moderate relative humidity with  good ventilation is essential for optimum storage. High humidity will promote decay. Although 50-70% R.H. will reduce decay during storage, significant weight loss will occur. For example, mature Kabocha squash lose 1.0 and 1.5% of their fresh weight per week of storage at 12.5°C (59°F) and 20°C (68°F), respectively. Weight loss of butternut squash stored at 12.5°C and 20°C was 2.5% and 5.5% per month, respectively.

Rates of Respiration

30-60 ml CO2/kg·hr at 25°C (77°F)

To calculate heat production, multiply ml CO2/kg·hr by 440 to get BTU/ton/day or by 122 to get kcal/metric ton/day.

Rates of Ethylene Production

2H4/kg·hr at 20°C

If the pumpkin or winter squash are chilled, ethylene production rates can be 3-5 times higher.

Responses to Ethylene

Exposure to ethylene will degreen squash with green rinds. Ethylene will also cause abscission of the stem, especially in less mature fruit.

Responses to Controlled Atmosphere (CA)

Atmospheres containing 7% CO2 can be beneficial by reducing loss of green color. Yellow squash, however, appear not to be benefited by 5 or 10% CO2 atmospheres. Lowering the O2 concentration does not appear to provide any benefit. Univ. of Georgia research showed that storing different pumpkin cultivars at 10°C (50°F) for 2-3 months in 3% O2 + 5% CO2 increased the percent of marketable fruit compared to pumpkins held at ambient conditions.

Temperature & Controlled Atmosphere Photos

Title: Butternut Squash Internal Breakdown when stored too long and/or at warm temperatures

Photo Credit: Marita Cantwell, UC Davis

Title: Butternut Squash Respiration Rate in Response to Chilling Injury

Photo Credit: Marita Cantwell, UC Davis

Title: Butternut Squash Stored 7 months

Photo Credit: Marita Cantwell, UC Davis

Disorders

Physiological and Physical Disorders

Chilling injury. Caused if pumpkins and squashes are stored below 10-12.5°C  (50-55°F). Symptoms of chilling injury are sunken pits on the surface and high levels of decay once fruit are removed from storage. Storing fruit 1 month at 5°C (41°F) is sufficient to cause chilling injury symptoms. Depending on the cultivar, storage for several months at 10°C (50°F) may cause some chilling injury (Photo 5). Changes in respiration rates will precede visible chilling injury symptoms (Photo 6). 

Freezing injury. Can occur at temperatures below -0.8°C (30.5°F).

Pathological Disorders

Several fungi are associated with decay during storage of pumpkins and winter squashes (See Disorder Photos). Fusarium, Pythium and anthracnose (Colletotrichum) and gummy stem blight or black rot (Didymella) (Photo 7, Photo 8) are common fungi. Alternaria rot (Photo 9) will develop on chill-damaged winter squashes. Fruit that are overmature at harvest (>2 weeks beyond optimal harvest date) will tend to have more storage decay. Rhizopus may develop rapidly on fruit that have been injured at harvest (Photo 10).

Special Considerations

Curing. The fruits may have tender rinds when freshly harvested. Curing in the field, with protection from the sun (Photo 13) by placing under the leaves, before handling and stacking into bins or wagons will help to harden or cure the rind. The recommended storage conditions also favor curing or hardening of the rind.

Disorders Photos

Title: Butternut Squash Alternaria Decay

Photo Credit: Marita Cantwell, UC Davis

Title: Butternut Squash Black Rot (Didymella bryoniae) 

Photo Credit: Zaccari, Fernanda

Title: Butternut Squash Black Rot (Didymella bryoniae) 

Photo Credit: Zaccari, Fernanda 

Title: Butternut Squash Rhizopus Decay resulting from harvest injury

Photo Credit: Marita Cantwell, UC Davis

Title: Butternut Squash Sunburn Damage evidenced by yellowish streaks. Degree of injury did not affect storage life.

Photo Credit: Marita Cantwell, UC Davis

Title: Kabocha Squash Blue Mold (Penicillium sp.) and Black Rot (Didymella bryoniae)

Photo Credit: Marita Cantwell, UC Davis

Title: Kabocha Squash Cladosporium Decay

Photo Credit: Marita Cantwell, UC Davis

Date

August 2014

Radicchio

Recommendations for Maintaining Postharvest Quality

radicchio089
Trevor V. Suslow and Marita Cantwell

Department of Plant Sciences, University of California, Davis

Maturity & Quality

Maturity Indices

Maturity is generally based on marketable size after threshold days beyond seed sowing has been reached (commonly 75 to 85 days). Some varieties transition from green to red or red-purple leaves at maturity or the onset of cool weather. Head-forming radicchio are firm and compact at maturity. Leaf raddichio have a long conical shape similar to Romaine lettuce. Radicchio should be harvested with a small stub of root remaining to help retain leaf attachment.

Quality Indices

Turgid leaves or firm, compact head with bright appearance typical of variety. Generally, bright white midribs with no cracking or splitting. Absence of marginal leaf necrosis, insect damage, harvest or packaging damage. Absence of bacterial decay at the root end.

Maturity & Quality Photos

Title: Quality

Photo Credit: Adel Kader, UC Davis

Temperature & Controlled Atmosphere

Optimum Temperature

Store at 0°C (32°F). Under these conditions, quality may be retained for 16 to 21 days. Radicchio are generally packed, after thorough precooling, with polymer film liners inside corrugated containers to prevent water loss.

Relative Humidity

95% or higher

Rates of Respiration

We have recently begun testing the respiration rates of radicchio. For guidance, use the following values:

7.5°C (45°F) 12ml CO2/kg·hr
20°C (68°F) 25ml CO2/kg·hr

Rates of Ethylene Production

Low, 0.6 to 1.0 µl C2H4/kg·hr at 20°C (68°F)

Response to Ethylene

Exposure to ethylene appears to increase marginal leaf browning and fungal decay. Accelerated pigmentation, pink to purple, of the white midribs occurred after 6 days at 10 ppm C2H4 and 7.5°C (45°F); = 98% R.H.

Responses to Controlled Atmospheres (CA)

The specific responses of radicchio to CA are not well defined at this time. Atmospheres of 3% O2 and 5% CO2 may be beneficial but low temperature is the best method for quality retention. In recent, preliminary, studies low oxygen conditions resulted in internal browning in head radicchio.

Disorders

Pathological Disorders

Radicchio are highly susceptible to Bacterial Soft Rot caused by Erwinia cartotovora at warmer storage temperatures and pectolytic Pseudomonas at lower refrigeration temperatures. Bacterial decay is common when harvesting methods cut across the basal leaves of head radicchio. Leaf margin necrosis and storage decay caused by Botrytis cinerea is also common, even with good temperature management.

Date

May 1999

Radish

Recommendations for Maintaining Postharvest Quality

radish090
Trevor Suslow

Department of Plant Sciences, University of California, Davis

Maturity & Quality

Maturity Indices

Radish (Raphanus sativus L.) is a diversely formed root vegetable and has many uses worldwide. Red and icicle radish are most common but Asian "daikon" types are increasing in popularity outside of countries such as Korea, Japan, Taiwan and China. The number of days post-seeding or emergence, which may vary from 30 to 70 days, depending on type, typically determines maturity. A minimum size standard for common red radish is 5/8 inch (1.6 cm) equatorial diameter. Current crop management practices stress rapid growth to ensure a mild flavor and crisp texture. Fertilization and irrigation management, or environmental conditions that slow growth may result in a woody texture and high pungency. Over-mature radish tends to be pithy (vacuolated) or spongy in texture and may develop harsh flavors, for most palates.

Quality Indices

Roots of Bunched or Topped Common Red Radish should, ideally, be of uniform and similar shape for the variety, well formed, smooth, firm but of tender texture, and free of growth or harvest damage, and free of decay, disease or insects. Bunched radish tops should be fresh in appearance, turgid, and free of freeze injury or other serious injury, seed stalk, yellowing or other discoloration, disease, decay, or insects.

U.S. Grade Standards effective October 1968 includes U.S. No. 1 and Commercial

Maturity & Quality Photos

Title: White Radish

Photo Credit: Adel Kader, UC Davis

Temperature & Controlled Atmosphere

Optimum Temperature

32°F (0°C)

Rapid cooling is essential to achieve the full storage potential of both bunched and topped roots. Radish is often top-iced to maintain temperature and contribute moisture for retaining a crisp texture. Under these conditions common red radish may be expected to maintain acceptable quality for 7 to 14 days with tops and 21 to 28 days if topped. Daikon-type radish may last from 3 to 4 months at these same conditions.

Optimum Relative Humidity

95-100%

Rates of Respiration

Common Red Radish:

Temperature 0°C (32°F) 5°C (41°F) 10°C (50°F) 20°C (68°F)
ml CO2/kg·hr        
Bunched 6-7 8-9 14-16 58-62
Topped 2-4 3-5 6-7 19-26

To calculate heat production multiply ml CO2/kg·hr by 440 to get Btu/ton/day or by 122 to get kcal/metric ton/day.

Rates of Ethylene Production

Very low;
Responses to Ethylene

Not Sensitive. Bunched tops may exhibit yellowing with prolonged storage and ethylene exposure.

Responses to Controlled Atmospheres(CA)

Atmospheres of 1 to 2% O2 and 2 to 3% CO2 are slightly beneficial in maintaining quality of topped radish when storage temperatures are 5 to 7°C (41 to 45°F). CA helps retard the re-growth of shoots and rootlets in "topped and tailed" roots. Even short exposure to temperatures above 7°C (45°F) will result in the development of off-flavors, browning, and soft-rot.

Disorders

Physiological and Physical Disorders

Freeze injury. As radish is, ideally, stored and transported just above the freezing point (30.5°F/-1.0°C), freeze injury is not uncommon. Shoots become water-soaked, wilted, and turn black. Roots appear water-soaked and glassy, often only at the outer layers if the freezing temperature is not too low. Roots become soft quickly on warming and pigmented roots may "bleed" (lose pigment).

Pathological Disorders

Bacterial Black Spot. (Xanthomonas campestris pv. vesicatoria) is a problem in some production locations and will develop in postharvest storage at warmer than optimum temperatures. Refrigeration is the primary control but washing roots in chlorinated water is reported to significantly control this disease.

Prompt cooling, chlorination, and refrigeration are also effective in controlling Bacterial Soft Rot (Erwinia carotovora subsp carotovora).

Rhizotonia spp. lesions may develop in storage at warmer than optimal temperatures but is more effectively controlled in the field. Botrytis (Grey Mold) and Sclerotinia (Watery Soft Rot) can develop, especially around harvest wounds, even at temperatures below 5°C (41°F) but is not common on radish in the U.S.

Date

May 2000

Spinach

Recommendations for Maintaining Postharvest Quality

spinach091
Trevor V. Suslow and Marita Cantwell

Department of Plant Sciences, University of California, Davis

Maturity & Quality

Maturity Indices

Spinach is selected for size and maximal recovery of clean leaves that are mid-maturity to young. Older and yellowing leaves are avoided when making the harvest cut. Generally 3-4 weeks of re-growth are required before a second harvest will yield adequate volume.

Quality Indices

Spinach, whether bunched or as leaves, should be uniformly green (generally not yellow-green), fully turgid, fairly clean, and free from serious damage. For bunched spinach, roots should be trimmed short to grade standards and petioles should be predominantly shorter than the leaf blade.

U.S. Grades: Bunched — U.S. No. 1, No. 2 (Oct. 1987). Leaves — U.S. Extra No. 1, No. 1, Commercial (Dec. 1946)

Temperature & Controlled Atmosphere

Optimum Temperature

0°C (32°F)

Spinach is highly perishable and will not maintain good quality for more than 2 weeks. Wilting, yellowing of leaves, and decay are likely to increase following storage beyond 10-14 days; faster at common distribution conditions of 5 to 10°C (41 to 50°F).

In a 1994 UC Davis study, an average of 17, 28, and 45% of leaves of 16 varieties had decay after 2, 3, and 4 weeks at 5°C, respectively. After the same periods at 5°C, 18, 25, and 45% of the leaves showed some yellowing. Commercial varities such as Imperial Spring, Shasta, Polka, Spectrum and Sporter had notably longer shelf- life than did varieties Bossanova, Spark and Space.

Optimum Relative Humidity

95-98%

Rates of Respiration

Temperature
°C
Temperature 
°F
ml CO2/kg·hr
0 32 9-11
5 41 17-29
10 50 41-69
15 59 67-111
20 68 86-143

To calculate heat production, multiply ml CO2/kg·hr by 440 to get BTU/ton/day or by 122 to get kcal/metric ton /day.

Rates of Ethylene Production


Responses to Ethylene

Spinach is highly sensitive to exogenous ethylene. Accelerated yellowing will result from low levels of ethylene during distribution and short-term storage. Do not mix loads such as apples, melons and tomatoes with spinach.

Responses to Controlled Atmosphere (CA)

Atmospheres of 7-10% O2 and 5-10% CO2 offer moderate benefit to spinach by delaying yellowing. Spinach is tolerant to higher CO2 concentration but no  increase in benefits has been observed. Package film for prewashed spinach leaves is selected to maintain 1-3% O2 and 8-10% CO2.

Disorders

Physiological and Physical Disorders

Freezing Injury. Freezing injury will be initiated at -0.3°C (31.5°F). Freezing  injury results in watersoaking typically followed by rapid decay by soft-rot bacteria.

Yellowing. Spinach is highly sensitive to exogenous ethylene (See Response to Ethylene).

Harvesting and handling should be done with care to prevent damage to the  petioles and leaves. Bunching ties should not be too tight as crushed or split petioles may lead to rapid decay.

Pathological Disorders

Bacterial Soft-Rot (primarily Erwinia and Pseudomonas) is a common problem.  Decay is usually associated with damaged leaves and stems.

Special Considerations

Package-icing and top-icing loads may be used. Frequent light misting may be done in displays to delay wilting of bunched spinach.

Date

May 1998

Sprouts, Seed

Recommendations for Maintaining Postharvest Quality

seed sprouts009 - Copy
Trevor Suslow and Marita Cantwell

Department of Plant Sciences, University of California, Davis

Maturity & Quality

Maturity Indices

Sprouts, plant seedlings consumed shortly after germination, are produced from many vegetable and agronomic plant seeds. Harvest maturity is highly regulated by germination (sprouting) conditions. The desired sprout length is the primary maturity index and harvesting is done at a relatively fixed number of days following radicle (root) emergence. Depending on seed type, harvest generally occurs 3 to 8 days after germination (Ex. alfalfa and sunflower, respectively). Examples of typical desired sprout lengths are given below:

Type Harvest Maturity (mm)
Adzuki 14 to 26
Alfalfa 26 to 38
Bean 26 to 38
Buckwheat 10 to 15
Brassica spp
(Broccoli, etc)
16 to 26
Garbanzo 26 to 36
Mung Bean 26 to 76
Radish 16 to 26
Wheat 10 to 15

Quality Indices

Sprouts should be clean, brightly colored for the type and free of damage, debris and decay. Bean sprouts should be etiolated (lacking noticeable green chlorophyll) with white root tips ( none to very limited browning). Sprouts are typically harvested and washed free of seed coats and non-germinated seed. If germinated in a solid medium rather than in hydroponic culture, sprouts are thoroughly washed to remove adhering materials.

Temperature & Controlled Atmosphere

Optimum Temperature

0°C (32°F)

Rapid cooling is essential to achieve the full storage potential of seed sprouts. Under these conditions most sprouts may be expected to maintain acceptable quality for 5 to 9 days. Shelf-life at 2.5°C (36°F) is less than 5 days, at 5°C (41°F), and at 10°C (50°F) is less than 2 days. The high respiration rates and perishable nature demand distribution and short-term storage at 0°C (32°F). Although industry experiences with Mung Bean suggest the potential for damage, no symptoms of chilling injury have been unequivocally linked to this temperature regime.

Optimum Relative Humidity

95-100%

Rates of Respiration

Mung Bean Sprouts:

Temperature 0°C (32°F) 5°C (41°F) 10°C (50°F) 20°C (68°F)
ml CO2/kg·hr 9-11 19-21 42-45 NR

To calculate heat production multiply ml CO2/kg·hr by 440 to get Btu/ton/day or by 122 to get kcal/metric ton/day.
NR - not recommended


Rates of Ethylene Production

Mung Bean:

Temperature 0°C (32°F) 5°C (41°F) 10°C (50°F)
ml/kg·hr 0.15 0.24 0.9

Responses to Ethylene

Low to medium sensitivity. Ethylene effects are not considered to be a significant factor in the optimal handling and distribution regimes for sprouts.

Responses to Controlled Atmospheres (CA)

Packing sprouts in plastic "clamshells" with limited venting or in perforated film pouches helps maintain quality. One report on mung bean sprouts (CA) demonstrated that 5% O2 + 15% CO2 extended keeping quality.

Disorders

Physiological and Physical Disorders

Freeze injury. Sprouts are susceptible to freeze injury but sensitivity varies widely. Shoots become water-soaked and turn black. Roots appear water-soaked and glassy. Roots become soft quickly on warming and darken rapidly.

Pathological Disorders

Bacterial Decay (Pantoea agglomerans = Erwinia herbicola, Pseudomonas fluorescens Biovar II, Pseudomonas marginalis, Pseudomonas viridiflava) is a common problem in many sprout types and will develop very rapidly in production systems as well as in postharvest storage, at warmer than optimum temperatures. High quality seed, proper pre-germination, seed treatments and postharvest refrigeration are the primary controls but washing sprouts in chlorinated or ozonated water (or other effective and approved disinfectant) will help control this decay and spoilage.

Special Considerations

Microbial Food Safety and Sanitation. Several types of seed sprouts have been clinically linked to several notable outbreaks of bacterial pathogens, especially in recent years. Multistate incidents of highly virulent Salmonella and enterohemorrhagic E. coli O157:H7 have been traced to the consumption of alfalfa, Mung bean, and possibly radish sprouts. Seed contamination has been positively identified as, at least, one confirmed source of contamination in several cases.

In 1998, the California Department of Health Services led a petition for Environmental Protection Agency (EPA) Section 18 registration of a 2% Ca(OCl)2 treatment for alfalfa seed as the best available method to ensure elimination of pathogens from seed. Full EPA Section 3 registration is expected in 2000. The International Sprout Growers association has endorsed this treatment as a voluntary industry-wide standard.

Organic sprout growers are at risk of losing their organic certification due to above limit residuals of hypochlorite. Alternative treatments are being actively investigated.

Date

May 2000

Squash (soft rind)

Recommendations for Maintaining Postharvest Quality

squash006
Trevor V. Suslow and Marita Cantwell

Department of Plant Sciences, University of California, Davis

Maturity & Quality

Maturity Indices

Summer squashes (soft-rind) are consumed at a range of physiological maturities but are defined as immature fruits of the diverse Cucurbitaceae family. Depending on cultivar and temperature, the time from flowering to harvest may be 45 to 60 days for zucchini, yellow straightneck or crookneck, and scallop (Patty Pan-type) squash and 75 days or more for many of the Sponge squash (immature gourds) such as Luffa. Fruit may be harvested at a very immature stage, at the desired fruit size, before seeds begin to enlarge and harden. A thin, soft external rind and external glossiness are also indicators of a pre-maturity condition. The entire fruit is edible, either raw or cooked, without removal of seeds and seed cavity tissue. Small, young fruit are tender and generally have a slightly sweet taste.

Quality Indices

Summer squash quality is based on uniform shape, tenderness of rind and internal tissue, overall firmness, a glossy skin color, and an intact well-trimmed stem portion. Uniformity of shape is an important quality factor and is defined to be characteristic of the type or variety, and free of twisting, groves, or other disproportionate growth defects. Size is not part of the United States Standard for grades but may be contractually specified as minimum or maximum diameter or length or both. Additional quality indices are freedom from growth or handling defects (discoloration, cuts bruises, abrasions, pitting) freedom from decay, and an absence of yellowing on dark green varieties.

U.S. Grades are No. 1 and No. 2 (effective Jan. 6, 1984)

Maturity & Quality Photos

Title: Summer Squash Discoloration Scale

Photo Credit: Marita Cantwell, University of California, Davis 

Temperature & Controlled Atmosphere

Optimum Temperature

5°C-10°C (41°F-50°F)

Summer squashes are not stored, ideally, for longer than 10 days. Zucchini squash has been stored at 5°C with acceptable market quality for up to two weeks. Storage at below 5°C for more than 3-4 days will generally result in chilling injury. Visual and sensory quality deteriorate and surface pitting and discoloration or browning progress rapidly following chilling injury . Shriveling, yellowing, and decay are likely to increase following storage beyond two weeks, especially upon removal to typical retail conditions.

Chilling Injury. Summer squash are chilling sensitive at temperatures below 5°C (41°F) if held for more than a day or two. Varieties vary in their chilling sensitivity (see table under special considerations). Consequences of chilling injury are water-soaked pitting, discoloration, and accelerated decay. Chilling injury is cumulative and may be initiated in the field prior to harvest.

Optimum Relative Humidity

95%

Rates of Respiration Production

Temperature 0°C (32°F) 5°C (41°F) 10°C (50°F) 15°C (59°F) 20°C (68°F)
ml CO2/kg·hr 6-7 7-10 17-18 37-45 42-48

To calculate heat production multiply ml CO2/kg·hr by 440 to get Btu/ton/day or by 122 to get kcal/metric ton/day.

Rates of Ethylene Production

0.1-1.0 µl/kg·hr at 20°C (68°F)

Responses to Ethylene

Summer squash varieties are low to moderately sensitive to exogenous ethylene. Accelerated yellowing of green types will result from low levels of ethylene during distribution and short-term storage.

Responses to Controlled Atmospheres

Controlled or modified atmosphere storage or shipping offer little benefit to summer squash quality maintenance. Low O2 levels (3-5%) delay yellowing in dark green varieties and delay the onset of decay by a few days. Zucchini tolerates elevated CO2 (less than or equal to 10%) but storage life is not greatly extended. Elevated CO2 (greater than or equal to 5%) has been reported to reduce chilling sensitivity in zucchini.

Disorders

Physiological and Physical Disorders

See Chilling injury.

Freezing Injury. Freezing injury will be initiated at -0.5°C (31.1°F). Symptoms of freezing injury include watersoaked patches on the soft rind or an outer ring of watersoaked pulp becoming brown and gelatinous in appearance over time.
Physical Injury

Harvesting should be done by cutting free of the vine rather than by snapping. A poorly trimmed stem-end is a quality defect because it promotes decay.

Bruising, scuffing, and compression injury are very common when attention to careful harvest and gentle handling practices are not followed.

Dehydration. Water loss is a serious and common postharvest problem for summer squash. Once harvested from the vine, loss of firmness and shriveling develop very rapidly unless cooled to the proper short-term storage temperatures.

Pathological Disorders

Diseases are an important source of postharvest loss, particularly in combination with physical injury or chilling stress. A large list of bacterial and fungal pathogens cause postharvest losses in transit, storage, and to the consumer. Alternaria alternata, Colletotrichum spp. (Anthracnose), Bacterial Rots, Cladosporium Scab, Pythium Cottony Leak, Didymella Black Rot, and Rhizopus Soft Rot are common disorders on summer squash.

Special Considerations

Summer squash are often treated with approved waxes or oils to reduce water loss, reduce abrasion injury and enhance appearance.

Included in the broad group of summer squash, are zucchini, cizelle, chayote, scallopini, yellow straightneck and crookneck, cucuza, Patty Pan, cocozelle, and marrow squash. Zucchini are considered the most chilling tolerant. Other types may maintain quality best during storage periods of 10-14 days at at slightly warmer temperatures (7.2°C (45°F)); 95% R.H. The relative susceptibility of summer squash varieties (green, yellow, crookneck and scalloped) to chilling injury is shown below. Squash were harvested June 1997 from a variety trial (established at Kearney Research Center in Parlier, California by Cooperative Extension Advisors Manuel Jimenez and Richard Molinar) and stored 10 days at 5°C (41°F) to evaluate visual quality and chilling symptoms.

Chilling Susceptibility Results
Low Intermediate High
Supersett, Tigress, Starship, El Greco, Prelude, Gentry, Gemma,BN 95044, BN 95055, Golden Gate, ZS-11
Multipid, Butter scallop, Debutant, Picasso, Rivera, General Patton, Enterprise, Supreme, Counselor, Excel
Meigs, Senator, HMX 6704, Golden Rod, Superpik, Elite, Sunburst, Monet, Fortune Golden Dwan III, Revenue, ZS-5

 

Date

August 1997

Sweet Potato

Recommendations for Maintaining Postharvest Quality

sweet potato002
Marita Cantwell and Trevor Suslow

Department of Plant Sciences, University of California, Davis

Maturity & Quality

General Information

The sweet potato (Ipomoea batatas) is a warm season root crop. Moist, sweet flesh types of sweetpotatoes are sometimes called "yams", but these should not be confused with true yams (Dioscorea sp.). Cultivars with high orange-colored flesh contain much higher levels of carotenoids than less pigmented types. Sweet potato flavor is largely based on starch and sugar concentrations, and these are affected by cultivars and storage conditions.

Maturity Indices

Sweet potatoes are harvested when roots have reached the desirable size. Irrigation is typically stopped 2 to 3 weeks before harvest so that vines begin drying before they are removed and roots are harvested.

Quality Indices

Good quality sweet potatoes should be smooth and firm, with uniform shape and size, be free from mechanical damage, and have a uniform peel color typical of the variety.

There are four U.S. Grades for sweet potato (U.S. Extra No. 1, U.S. No.1, U.S. commercial and U.S. No. 2), and grades are based on degree of freedom from defects (dirt, roots, cuts, bruises, growth cracks, decay, insects, and diseases), but also size and weight categories.

Temperature & Controlled Atmosphere

Optimum Temperature

The recommended conditions for commercial storage are to keep roots cool and dry. Sweet potato roots are chilling sensitive and should be stored between 12.5°C and 15°C (55°F to 59°F) with high relative humidity (>90%). A storage life of 6-10 months can be expected under these conditions, although sprouting may begin to occur after about 6 months depending on cultivar. Temperatures above 15°C (59°F) lead to more rapid sprouting and weight loss. Careful handling during harvesting will minimize mechanical damage to the skin and reduce decay incidence during storage. Roots are not washed before storing in bins or crates, but only after removal for selection and packing for marketing. Sweet potato roots are commonly stored in evaporatively cooled rooms, supplemented by mechanical refrigeration late in the storage period when warm ambient temperatures occur.

Optimum Relative Humidity

>95% for long-term storage; 70-90% for short-term handling for marketing

Rates of Respiration

Temperature 10°C (50°F) 15°C (59°F) 25°C (77°F)
ml CO2/kg·hr
Cured 7 10 - 12 ---
Noncured --- 15 27 - 35

To calculate heat production multiply mL CO2/kg·hr by 440 to get Btu/ton/day or by 122 to get kcal/metric ton/day.

Rates of Ethylene Production and Responses to Ethylene

Sweet potato roots produce very low amounts of ethylene (~0.1 µL/kg·hr), although much higher rates can occur after chilling, wounding and decay development. Exposure to ethylene (1 to 10 ppm) increases respiration rates and phenolic metabolism and adversely affects flavor and color of cooked roots.

Responses to Controlled Atmospheres (CA)

There is no commercial use of controlled atmospheres for sweet potato storage. Respiration rates of roots are reduced as oxygen is lowered from 21 to 3%. Oxygen concentrations below 3% may results in increased respiration rates due to fermentative metabolism. Response of roots to increased carbon dioxide levels is not known.

Disorders

Physiological and Physical Disorders

Chilling injury. Sweet potato roots are very sensitive to chilling injury at temperatures of 12.5°C (55°F) or below. Symptoms of chilling injury include fungal decay, internal pulp browning, and root shriveling. Chilled roots that have been cooked can have "hardcore" defect and a darker color than non-chilled roots.

Pathological Disorders

Chilling and mechanical injury predispose sweet potatoes to decay, especially Rhizopus soft rot. Postharvest fungicides may be applied to reduce the risk of Rhizopus after handling for marketing. There are numerous other decay-causing fungi including black rot (Ceratocystis) and Fusarium rot. Seed piece treatment and postharvest curing are the main control measures for these organisms. In warm wet production conditions, bacterial rots can also cause postharvest losses.

Special Considerations

Curing. The periderm of sweetpotato roots is easily damaged during harvest and handling, and this leads to an unsightly appearance, high rates of water loss, and increased susceptibility to decay. The process of curing the damaged skin or "wound healing" can be achieved by holding roots at 25-32°C (77-90°F) under high relative humidity (>90 to 100%) for several days to 1 week. The conditions for curing sweetpotatoes are similar to those used for other tropical root and tuber crops. Growers often load bins of warm roots into storage rooms and do not turn on the fans for evaporative cooling until after about 1 week. This interval before cooling provides the warm humid conditions necessary for curing wounds.

Disorders Photos

Title: Botryodiplodia Rot

Photo Credit: Don Edwards, UC Davis

Title: Chilling Injury (2)

Photo Credit: Leonard Morris, UC Davis

Title: Fusarium Rot

Photo Credit: Don Edwards, UC Davis

Title: Genotypic Difference in Chilling Injury (1)

Photo Credit: Leonard Morris, UC Davis

Title: Rhizopus Rot (1)

Photo Credit: Don Edwards, UC Davis

Title: Rhizopus Rot (2)

Photo Credit: Don Edwards, UC Davis

Title: Surface Abrasions

Photo Credit: Marita Cantwell, UC Davis

Date

August 2001

Tomatillo (Husk Tomato)

Recommendations for Maintaining Postharvest Quality

tomatillo003
Marita Cantwell

Department of Plant Sciences, University of California, Davis

Maturity & Quality

Maturity Indices

The tomatillo or husk tomato (Physalis ixocarpa) is a small, spherical and green or green-purple fruit surrounded by an enlarged calyx or "husk." As the fruit matures, it fills the husk and can split it open by harvest. Tomatillos are the key ingredients in fresh and cooked green salsas and other Latin American dishes. The freshness and greenness of the husk is a quality criteria. Fruit should be firm, bright green as the green color and acidic flavor are the main culinary contributions of tomatillos.

Quality Indices

Tomatillos can be harvested at various stages of development. For commercial marketing, they should be harvested when the fruits are well formed and have substantially filled the husk but are still bright green in color. Overmature fruit are light green or yellowing and should be avoided since they are sweeter and undesirable for most uses.

Maturity & Quality Photos

Title: De-husked Tomatillos

Photo Credit: Marita Cantwell, UC Davis

Title: Maturity Stages

Photo Credit: Marita Cantwell, UC Davis

Title: Quality

Photo Credit: Marita Cantwell, UC Davis

Title: Tomatillo with Green Husks

Photo Credit: Marita Cantwell, UC Davis

Temperature & Controlled Atmosphere

Optimum Temperature

Tomatillos can be forced-air or room cooled. The main reason to cool rapidly is to retain the fresh appearance of the husk. Tomatillos can be stored under a wide range of conditions. At ambient temperatures, the husks will dry, but the fruit will remain in good condition for about 1 week. For longer storage life temperatures of 5°C to 10°C (41°F to 50°F) with moderate humidity levels (80-90% RH) are recommended to retain the freshness of the fruit and the husk. At 5°C (41°F) chilling injury will occur after about 3 weeks.

Optimum Relative Humidity

80-90%

Rates of Respiration

Temperature 5°C (41°F) 10°C (50°F) 20°C (68°F)
ml CO2/kg·hr 6-7 7-10 15-20

To calculate heat production multiply ml CO2/kg·hr by 440 to get Btu/ton/day or by 122 to get kcal/metric ton/day.
Respiration data are for mature fruit. Respiration rates remain relatively constant during storage at 5°C and 10°C; rates decrease during storage at 20°C. Respiration rates of developing fruit are about 25% higher than those of mature fruit.

Rates of Ethylene Production

Tomatillos produce low amounts of ethylene at immature (0.5 to 2 µl/kg·hr at 10 to 20°C [50 to 68°F]) and mature stages (1 to 10 µl/kg·hr ). At horticulturally overmature stages, i.e. when the fruit show yellow color change due to ripening, ethylene production rates can be high (20-40 µl/kg·hr at 20°C (68°F)).

Responses to Ethylene

Exposure of mature fruit to ethylene causes undesirable color change.

Responses to Controlled Atmospheres (CA)

No information is available.

Disorders

Physiological and Physical Disorders

Chilling injury. Tomatillos can be stored at 10°C (50°F) for 1 month without any symptoms of chilling injury. After 3 weeks at 5°C (41°F), the fruit began to show chilling symptoms, and at 2.5°C (36°F), fruit showed significant amounts of chill-induced decay. Typical chilling symptoms include surface pitting and decay.

Pathological Disorders

Chilling injury can result in the appearance of black mold on the fruit due to Alternaria alternata, the same organism found on chill injured tomatoes and peppers. Superficial molds occur on the husk during storage under high humidity conditions, but have not been identified. Washing in chlorinated water reduces superficial mold growth, but may be difficult to implement commercially since it is difficult to remove all moisture from inside the husk.

Disorders Photos

Title: Quality of Fresh and Stored

Photo Credit: Marita Cantwell, UC Davis

Date

August 2000

Tomato

Recommendations for Maintaining Postharvest Quality

tomato014
Trevor V. Suslow and Marita Cantwell

Department of Plant Sciences, University of California, Davis

Maturity & Quality

Maturity Indices

Standard Tomatoes. Minimum harvest maturity (Mature Green 2) is defined by internal fruit structure indices. Seeds are fully developed and are not cut upon slicing the fruit. Gel formation is advanced in at least one locule and jellylike material is forming in other locules.

ESL Tomatoes.* Off-vine ripening is severely affected if fruit are harvested at the MG2 stage. Minimum harvest maturity is better defined as equivalent to ripeness class Pink (USDA Color Stage 4 more than 30 percent but no more than 60 percent of the fruit surface, overall, shows a pink-red color.)

*Extended Shelf-Life trait is due, in part, to either the presence of the rin or nor gene.

Quality Indices

Standard tomato quality is primarily based on uniform shape and freedom from growth or handling defects. Size is not a factor of grade quality but may strongly influence commercial quality expectations.

Shape. Well formed for type (round, globe, flattened globe, roma)

Color. Uniform color (orange-red to deep red; light yellow). No green shoulders.

Appearance. Smooth and small blossom-end scar and stem-end scar. Absence of growth cracks, catfacing, zippering, sunscald, insect injury, and mechanical injury or bruises.

Firmness. Yields to firm hand pressure. Not soft and easily deformed due to an overripe condition.

U.S. grades are No. 1, Combination, No. 2, and No. 3. Distinction among grades is based predominantly on external appearances, bruising and firmness.

Greenhouse grown tomatoes are graded as U.S. No. 1 or No. 2 only.

Maturity & Quality Photos

Title: Cherry Tomato Maturity & Ripeness

Photo Credit: Adel Kader, UC Davis

Title: Grape Tomato Maturity & Ripeness

Photo Credit: Marita Cantwell, UC Davis

Title: Tomato Maturity Stages

Photo Credit: Marita Cantwell, UC Davis

Title: USDA Color Chart

Photo Credit: Adel Kader, UC Davis

Temperature & Controlled Atmosphere

Optimum Temperature

Mature Green: 12.5-15°C (55-60°F)
Light Red (USDAColor Stage 5): 10-12.5°C (50-55°F)
Firm-ripe (USDA Color Stage 6): 7-10°C (44-50°F) for 3-5 days

Mature-green tomatoes can be stored up to 14 days prior to ripening at 12.5°C (55°F) without significant reduction of sensory quality and color development. Decay is likely to increase following storage beyond two weeks, at this temperature. Typically 8-10 days of shelflife are attainable within the optimum temperature range after reaching the Firm-ripe stage. Short term storage or transit temperatures below this range are used by some in the trade but will result in chilling injury after several days. Extended storage with controlled atmosphere has been demonstrated. (See Responses to CA)

Ripening Temperatures

18-21°C (65-70°F); 90-95% R.H. for standard ripening 14-16°C (57-61°F) for slow ripening (i.e. in transit).For more details on ripening conditions see Ripening.

Chilling Injury. Tomatoes are chilling sensitive at temperatures below 10°C (50°F) if held for longer than 2 weeks or at 5°C (41°F) for longer than 6-8 days. Consequences of chilling injury are failure to ripen and develop full color and flavor, irregular (blotchy) color development, premature softening, surface pitting, browning of seeds, and increased decay (especially Black mold caused by Alternaria spp.). Chilling injury is cumulative and may be initiated in the field prior to harvest.

Optimum Relative Humidity

90-95%

High relative humidity is essential to maximize postharvest quality and prevent water loss (desiccation). Extended periods of higher humidity or condensation may encourage the growth of stem-scar and surface molds.

Rates of Respiration

Temperature

ml CO2/kg·hr
Mature-Green Ripening Green Ripening
5°C (41°F)  3-4 NR
10°C (50°F) 6-9 7-8
15°C (59°F) 8-14 12-15
20°C (68°F)  14-20 12-22
25°C (77°F)   18-26 15-26

To calculate heat production, multiply ml CO2/kg·hr by 440 to get BTU/ton/day or by 122 to get kcal/metric ton /day.
NR - not recommended for more than a few days due to chilling injury.

Rates of Ethylene Production

1.2-1.5µl/kg·hr at 10°C (50°F)
4.3-4.9µl/kg·hr at 20°C (68°F)

Responses to Ethylene

Tomatoes are sensitive to exogenous ethylene and exposure of mature-green fruit to ethylene will initiate ripening. Ripening tomatoes produce ethylene at a moderate rate and co-storage or shipment with sensitive commodities, such as lettuce and cucumbers, should be avoided.

Ripening

Faster ripening results from higher temperatures between 12.5-25°C (55-77°F); 90-95% R.H.; 100 ppm ethylene. Good air circulation must be maintained to ensure temperature uniformity within the ripening room and to prevent the accumulation of CO2. CO2 (above 1%) retards the action of ethylene in stimulating ripening.

The optimum ripening temperature to ensure sensory and nutritive quality is 20°C (68°F). Color development is optimal and retention of vitamin C content is highest at this ripening temperature. Tomatoes allowed to ripen off-the-vine above 25°C (77°F) will develop a more yellow and less red color and will be softer.

Ethylene treatment typically extends for 24-72 hours. A second treatment period may follow repacking if immature green fruit were included in the harvest.

Responses to Controlled Atmospheres (CA)

Controlled atmosphere storage or shipping offer a moderate level of benefit. Low O2 levels (3-5%) delay ripening and the development of surface and stem-scar molds without severely impacting sensory quality for most consumers. Storage times of up to 7 weeks have been reported for tomatoes using a combination of 4% O2, 2% CO2, and 5% CO2. More typically, 3% O2 and 0-3% CO2 are used to maintain acceptable quality for up to 6 weeks prior to ripening. Elevated CO2 above 3-5 % is not tolerated by most cultivars and will cause injury. Low O2 (1%) will cause off-flavors, objectionable odors, and other condition defects, such as internal browning.

Temperature & Controlled Atmosphere Photos

Title: High Temperature Effects

Photo Credit: Adel Kader, UC Davis

Title: Temperature Effects on Tomato

Photo Credit: Don Edwards, UC Davis

Title: Tomato Ethephon Effects

Photo Credit: Adel Kader, UC Davis

Title: Tomato Low Oxygen Effects

Photo Credit: Adel Kader, UC Davis

Title: Tomato Respiration vs Ripening

Photo Credit: Adel Kader, UC Davis

Title: Tomato SO2 Damage

Photo Credit: Adel Kader, UC Davis

Disorders

Physiological and Physical Disorders

See Chilling injury.

Freezing Injury. Freezing injury will be initiated at -1°C (30°F), depending on the soluble solids content. Symptoms of freezing injury include a watersoaked appearance, excessive softening, desiccated appearance of the locular gel.

Tomatoes are sensitive to many production and environment-genetic interaction disorders which may be manifested during postharvest ripening or postharvest inspection. Fertilizer and irrigation management, weather conditions, insect feeding injury, asymptomatic virus infection, and unknown agents may interact to affect postharvest quality. Examples are Blossom-end Rot, Internal White Tissue, Rain Checking, Concentric and Radial Cracking, Puffiness, Persistent Green Shoulder, and Graywall. Several references with photographic keys to disorders are available.

Pathological Disorders

Diseases are an important source of postharvest loss depending on season, region and handling practices. Commonly, decay or surface lesions result from the fungal pathogens Alternaria (Black Mold Rot), Botrytis (Gray Mold Rot), Geotrichum (Sour Rot), and Rhizopus (Hairy Rot).

Bacterial Soft Rot. Caused by Erwinia spp. can be a serious problem particularly if proper harvest and packinghouse sanitation is not used.

Treatment with hot air or hot water immersion (55°C for 0.5-1.0 min.) has been effective in preventing surface mold but has not been used extensively for commercial treatments. CA can be effective in delaying fungal growth on the stem-end and fruit surface.

Greenhouse tomatoes marketed on-the-vine ("cluster tomatoes") are very susceptible to Botrytis Gray Mold, especially if film-wrapped in a tray.

Special Considerations

Rapid cooling soon after harvest is essential for optimal postharvest keeping quality. The precooling endpoint is typically 12.5°C (55°F). Forced-air cooling is the most effective practice but room cooling is more common.

[For more information, see our publication “ Fruit Ripening & Ethylene Management ”, available for purchase using our Publication order form .]

Disorders Photos

Title: Tomato Alternaria from Chilling

Photo Credit: Don Edwards, UC Davis

Title: Tomato Alternaria Rot (1)

Photo Credit: Don Edwards, UC Davis

Title: Tomato Alternaria Rot (2)

Photo Credit: Don Edwards, UC Davis

Title: Tomato Athracnose

Photo Credit: Don Edwards, UC Davis

Title: Tomato Blossom-end Rot

Photo Credit: Marita Cantwell, UC Davis

Title: Tomato Bruising Scores

Photo Credit: Adel Kader, UC Davis

Title: Tomato Buckeye Rot

Photo Credit: Don Edwards, UC Davis

Title: Tomato Checker-boarding & Mechanical Damage

Photo Credit: Adel Kader, UC Davis

Title: Tomato Chilling Injury

Photo Credit: Adel Kader, UC Davis

Title: Tomato Ghost Spots

Photo Credit: Don Edwards, UC Davis

Title: Tomato Phytophthora (1)

Photo Credit: Adel Kader, UC Davis

Title: Tomato Phytophthora (2)

Photo Credit: Adel Kader, UC Davis

Title: Tomato Radial and Concentric Cracking

Photo Credit: Adel Kader, UC Davis

Title: Tomato Rhizopus Rot

Photo Credit: Don Edwards, UC Davis

Title: Tomato Shoulder Bruise

Photo Credit: Adel Kader, UC Davis

Title: Tomato Solar Yellowing (1)

Photo Credit: Adel Kader, UC Davis

Title: Tomato Solar Yellowing (2)

Photo Credit: Adel Kader, UC Davis

Title: Tomato Sour Rot (1)

Photo Credit: Don Edwards, UC Davis

Title: Tomato Sour Rot (2)

Photo Credit: Don Edwards, UC Davis

Title: Tomato Stemphyllium Rot

Photo Credit: Don Edwards, UC Davis

Title: Tomato Sun Scald

Photo Credit: Adel Kader, UC Davis

Title: Tomato Vibration Damage

Photo Credit: Adel Kader, UC Davis

Title: Tomato Fusarium Rot

Photo Credit: Don Edwards, UC Davis

Date

May 1997

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