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Recommendations for Maintaining Postharvest Quality

Elizabeth J. Mitcham, Carlos H. Crisosto and Adel A. Kader
Department of Pomology, University of California, Davis, CA 95616

Maturity Indices
Firmness of 18 pounds-force, core clear of starch. Firmness (lbs-f) x soluble solids (%) x starch score (1 to 6 scale) should equal 250 at initiation of harvest.

Quality Indices
Firmness, crispness, lack of mealiness

Flavor, including soluble solids, titratable acidity and flavor volatiles.

Freedom from defects such as bruising, decay, stem or blossom-end cracks, bitter pit, scald, internal browning, shrivel or watercore.

Red skin color intensity and uniformity.

Optimum Temperature
0°C ± 1°C (32°F ± 2°F); Freezing temperature: -1.7°C (29°F)

Optimum Relative Humidity
90-95% RH

Rates of Respiration

Temperature 0°C (32°F) 5°C (41°F) 10°C (50°F) 20°C (68°F)
ml CO2/ kg·hr 2-5 3-7 5-10 12-25

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.

1 Higher rates for riper apples.

Rates of Ethylene Production

Temperature 0°C (32°F) 5°C (41°F) 10°C (50°F) 20°C (68°F)
µl/ kg·hr 1-10 2-20 5-40 20-125

11 Higher rates for riper apples.

Responses to Ethylene
Ethylene stimulates ripening. Mixed results on the benefits of scrubbing ethylene from storage rooms, depending on harvest maturity and type of storage (air or CA).

Responses to Controlled Atmospheres (CA)
Fruit to be stored longer than 1 month benefit from CA storage in terms of retention of acidity and firmness and reduction of scald incidence and severity. CA storage potential is up to 10 months (vs. 6 months in air).

Recommended atmosphere: 1 to 2% O 2 + 2 to 4% CO 2

Physiological Disorders
Bruising. Can be excessive. Gentle handling is important.

Watercore. Can be important later in the harvest season. Water-soaking of the flesh near the core due to an accumulation of sorbitol in the intercellular spaces. Market promptly to avoid internal browning and breakdown.

Bitter Pit. Sunken brown spots on the skin, especially at the calyx end, related to low calcium concentration in the apple. Best controlled by calcium sprays prior to harvest and calcium dips prior to cold storage. Reduced incidence with controlled atmosphere storage.

Superficial Scald. Browning of the skin which develops in cold storage. High susceptibility. Use diphenylamine at label rates. Controlled atmosphere storage delays onset. Ultra-low oxygen CA storage has been effective in some growing areas.

Controlled Atmosphere Damage. Oxygen concentrations below 1% and/or CO2levels above 10% may induce off-flavor associated with fermentative metabolites. Elevated CO2 injury sypmtoms include partially sunken brown lesions on skin and/or internal browning and cavities. Low O2 injury can result in a purple cast to the skin of Red Delicious apples.

Pathological Disorders
Moldy Core. Caused by several fungi including Alternaria sp., Fusarium sp.,Aspergillus and Penicillium. Red Delicious apples are particularly susceptible because of the open or deep sinus cavity. Drenching can increase the incidence of moldy core.

Blue Mold and Grey Mold. The two most important postharvest diseases of Red Delicious apples are caused by Penicillium expansum and Botrytis cinerea. Both fungi are wound pathogens. Sanitation is critical to control of these diseases. Drenching can spread spores of Penicillium and Botrytis to wounds from harvest operations. Use of fungicides during drenching may reduce decay.

Postharvest Technology Research and Information Center
Department of Pomology
University of California
One Shields Ave., Davis, CA 95616-8683Send comments and questions to Postharvest Technology Research and Information Center
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