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Carrot

Recommendations for Maintaining Postharvest Quality

Trevor V. Suslow, Jeffrey Mitchell and Marita Cantwell

Department of Plant Sciences, University of California, Davis

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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.