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Kiwifruit

Recommendations for Maintaining Postharvest Quality

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

Department of Plant Sciences, University of California, Davis

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Kiwifruit PDF

Maturity & Quality

Maturity Indices

Minimum of 6.5% soluble solids content (SSC) at harvest
Minimum flesh firmness of 14 lbf (penetration force with an 8-mm = 5/16 inch tip). Late harvested kiwifruits retain their firmness better than early harvested fruit and have higher SSC at harvest and when ripe

Quality Indices

Freedom from growth cracks, insect injury, bruises, scars, sunscald, internal breakdown, and decay
Minimum of 14% SSC when ripe (ready to eat); a kiwifruit at 2-3 lb flesh firmness is considered ripe
Kiwifruits are a good source of vitamin C

Maturity & Quality Photos

Title: Starch Disappearance Chart

Photo Credit: Don Edwards, UC Davis

Temperature & Controlled Atmosphere

Optimum Temperature

0°C (32°F); highest freezing point is -1.5°C (29.3°F)

Optimum Relative Humidity

90-95%

Rates of Respiration

Temperature	0°C (32°F)	5°C (41°F)	10°C (50°F)	15°C (59°F)	20°C (68°F)
Rates of Respiration ml CO₂/kg·hr	1.5-2.0	3-4	5-7	9-12	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.

Rates of Ethylene Production

Less than 0.1 µl/kg·hr at 0°C (32°F), 0.1-0.5 µl/kg·hr at 20°C (68°F) for Production unripe kiwifruit. Ripe kiwifruit (less than 4 lbf firmness) produce 50-100 µl/kg·hr at 20°C (68°F).

Responses to Ethylene

Kiwifruits are extremely sensitive to ethylene. As little as 5-10 ppb ethylene will induce fruit softening
Avoid exposure of unripe kiwifruits to ethylene during harvest, transport, and storage unless accelerated ripening is desired. In such a case, kiwifruits can be exposed to 100 ppm ethylene for 12 hours at 0 to 10°C (32 to 68°F) and 90-95% humidity; the higher the temperature the faster the ripening rate.

Responses to Controlled Atmospheres (CA)

Optimum CA: 1-2% O₂ + 3-5% CO₂
CA delays ripening and retains flesh firmness
CO₂ levels above 7% can cause internal breakdown of the flesh
CA must be established within 2 days after harvest to maximize benefits; ethylene concentration should be kept below 20 ppb to avoid accelerated flesh softening and incidence of white core inclusions

Disorders

Physiological and Physical Disorders

Freezing Damage. Flesh translucency starting at the stem end of the fruit and progressing toward the blossom end as the severity increases. Susceptible fruit become somewhat yellow fleshed with prolonged storage. There was no "graininess" observed in the fruit that showed these symptoms. Freezing damage can occur on early picked kiwifruit when stored at temperatures below 0°C (32°F) or when subjected to an early frost in the vineyard. Fruit frosted late in the season are usually affected on the shoulder where the cells collapse to cause a pinching of the fruit at the stem end.

Hard-Core. This disorder is induced by exposure of kiwifruit to ethylene plus carbon dioxide levels above 8 percent. The fruit core fails to ripen when the remainder of the fruit is soft and ripe.

Internal Breakdown. These symptoms start as a slight discoloration (water soaking) at the blossom end of the fruit. With time this progresses around the blossom end and ultimately encompasses a large part of the fruit. As symptoms progress a "graininess" develops below the fruit surface beginning in the area around the blossom end of the fruit.

Pericarp Granulation. The occurrence of granulation is predominantly at the stylar end of the fruit, but as in the case of translucency may extend up the sides of fruit. This disorder also is more severe with prolonged storage and after ripening at 20°C (68°F). There is no obvious correlation between pericarp translucency and granulation since symptoms can occur independently.

Pericarp Translucency. This disorder has been noted in both air- and CA-stored kiwifruit at 0°C (32°F). It appears as translucent patches in the outer pericarp tissue at the stylar end which may extend up the sides of the fruit. Pericarp translucency is more severe after prolonged storage, but it can be observed after 12 weeks of storage at 0°C (32°F). The presence of ethylene in the storage atmosphere exacerbates symptom development.

White-Core Inclusions. The occurrence of white-core inclusions is directly related to the presence of ethylene in CA storage. This disorder results in distinct white patches of core tissue that are obvious in ripe fruit. Symptoms have been observed as early as 3 weeks after storage at 0°C (32°F).

Pathological Disorders

Several pathogens can cause postharvest deterioration of kiwifruit. Botrytis gray mold rot caused by Botrytis cinerea is the most important and can directly invade the fruit or enter through wounds. Kiwifruit become much more susceptible to Botrytis (and other fungi) as they soften. Thus, maintaining fruit firmness (by rapid cooling, cold storage, and use of controlled atmospheres) can significantly reduce pathological breakdown. Sunburned fruit and physically damaged fruit are also more susceptible to postharvest diseases.

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

Disorders Photos

Title: Alternaria Rot (1)

Photo Credit: Don Edwards, UC Davis

Title: Alternaria Rot (2)

Photo Credit: Don Edwards, UC Davis

Title: Ammonia Damage

Photo Credit: Don Edwards, UC Davis

Title: Botrytis Nest Rot

Photo Credit: Don Edwards, UC Davis

Title: Botrytis Stem End Rot

Photo Credit: Don Edwards, UC Davis

Title: Dothiorella Stem End Rot

Photo Credit: Don Edwards, UC Davis

Title: Freezing Injury

Photo Credit: Don Edwards, UC Davis

Title: Granulation

Photo Credit: Don Edwards, UC Davis

Title: Impact Bruising

Photo Credit: Don Edwards, UC Davis

Title: Ink Staining

Photo Credit: Don Edwards, UC Davis

Title: Penicillium Stem End Rot

Photo Credit: Don Edwards, UC Davis

Title: Phoma Rot

Photo Credit: Don Edwards, UC Davis

Title: Phoma Stem End Rot

Photo Credit: Don Edwards, UC Davis

Title: Severe Water Loss

Photo Credit: Adel Kader, UC Davis

Title: Translucency

Photo Credit: Don Edwards, UC Davis

Title: Vibration Damage

Photo Credit: Don Edwards, UC Davis

Title: White Inclusion

Photo Credit: Don Edwards, UC Davis

Date

February 1996

Use of Materials

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Except for these specified uses, no part of the textual materials available on the UC Postharvest Technology Center Web site may be copied, downloaded, stored in a retrieval system, further transmitted or otherwise reproduced, stored, disseminated, transferred or used, in any form or by any means, except as permitted herein or with the University of California's prior written agreement. Request permission from UC Postharvest Technology Center. Distribution for commercial purposes is prohibited.

The information in this fact sheet represents our best understanding of the current state of knowledge at the time of the latest update, and does not represent an exhaustive review of all research results. Links to any of these UC Postharvest Technology Center pages are permitted, but no endorsement of the linking site or products mentioned in the linking page is intended or implied by such a link.

How to Cite

Author(s) names. Initial publication or update date (located at the top). Title. Link to the specific Produce Fact Sheet webpage (Accessed date)

Example: Cantwell, M. and T. Suslow. 2002. Lettuce, Crisphead: Recommendations for Maintaining Postharvest Quality.

http://ucanr.edu/sites/Postharvest_Technology_Center_/Commodity_Resources/Fact_Sheets/Datastores/Vegetables_English/?uid=19&ds=799 (Accessed January 18, 2014).

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