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Recommendations for Maintaining Postharvest Quality

Mary Lu Arpaia¹ and Adel A. Kader^2
1Department of Botany and Plant Sciences, University of California, Riverside, CA 92521
²Department of Pomology, University of California, Davis, CA 95616

Maturity Indices
Color (yellow, orange, and/or red) on 75% of fruit surface and soluble solids/acid ratio of 6.5 or higher.

Quality Indices
Color intensity and uniformity; size; shape; firmness; freedom from decay; and freedom from defects including freezing injury, chilling injury, insect damage, and scars. Flavor depends upon soluble solids/acid ratio and absence of off-flavors.

Optimum Temperature
5-8°C (41-46°F) for 2 to 6 weeks, depending on cultivar, maturity-ripeness stage at harvest, and decay control treatments used.

Optimum Relative Humidity
90-95%

Rates of Respiration

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 µl/kg·hr at 20°C (68°F)

Responses to Ethylene
Mandarins and tangerines can be degreened by exposure to 1-10 ppm ethylene for 1-3 days at 20 to 25°C (68 to 77°F)

Removal of ethylene from transport vehicles and storage facilities for citrus fruits can help reduce decay incidence.

Responses to Controlled Atmospheres (CA)
A combination of 5-10% O₂ and 0-5% CO₂ can delay color changes from green to yellow and other symptoms of senescence, but it is not very effective in decay control. Mandarins do not tolerate exposure to fungistatic CO₂ levels (10-15%). Commercial use of CA is very limited.

Physiological Disorders
Chilling injury. Symptoms include pitting and brown discoloration followed by increased susceptibility to decay. Severity increases with longer exposures to lower temperature below 5°C (41°F).

Oil spotting (Oleocellosis). Harvesting and handling turgid citrus fruits can result in breaking of oil cells and release of oil that damages surrounding tissues.

Aging. Symptoms include shriveling and peel injury around the stem end.

Pathological Disorders
Major Diseases:

• Green mold (Penicillium digitatum)
• Blue mold (Penicillium italicum)
• Phomopsis stem-end rot (Phomopsis citri)
• Stem end rot (Lasiodiplodia theobromae)
• Brown rot (Phytophthora citrophthora)
• Anthracnose (Colletotrichum gloeosporioides)

Control Strategies:
Reduce the pathogen population in the environment

1. Effective preharvest disease control.
2. Use of chlorine in wash water.
3. Heat treatments.
4. Effective sanitation procedures

Maintain fruit resistance to infection

1. Minimize mechanical injuries.
2. Use proper ranges of temperatures and relative humidity throughout postharvest handling.
3. Use postharvest fungicides and/or biological antagonists.
4. Avoid exposure to ethylene.

Postharvest Technology Research and Information Center
Department of Pomology
University of California
One Shields Ave., Davis, CA 95616-8683
Send comments and questions to Postharvest Technology Research and Information Center
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Produce/ProduceFacts/Fruit/mandarin.html updated July 3, 2000