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Recommendations for Maintaining Postharvest Quality

Mary Lu Arpaia1 and Adel A. Kader2
1Department of Botany and Plant Sciences, University of California, Riverside, CA 92521
2Department of Pomology, University of California, Davis, CA 95616

Maturity Indices
Soluble solids/acid ratio of 8 or higher and yellow-orange color at least on 25% of the fruit surface or soluble solids/acid ratio of 10 or higher and green-yellow color on 25% or greater of the fruit surface.

Quality Indices
Color intensity and uniformity; firmness; size; shape; smoothness; freedom from decay; and freedom from defects including physical damage (abrasions and bruising ), skin blemishes and discoloration, freezing damage, chilling injury, and insect damage. Flavor quality is related to soluble solids/acid ratio and absence of off-flavor-causing compounds including fermentative metabolites.

Optimum Temperature
3-8°C (38-46°F) for up to 3 months, depending on cultivar, maturity-ripeness stage at harvest and production area. Some Florida-grown cultivars can be kept at 0-1°C (32-34°F). Arizona-grown Valencia oranges should be kept at 9°C (48°F).

Optimum Relative Humidity

Rates of Respiration

Temperature 5°C (41°F) 10°C (50°F) 15° (59°F) 20° (68°F)
ml CO2/ kg·hr 2-4 3-5 6-12 11-17

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
Exposure to 1-10ppm ethylene for 1-3 days at 20-30°C (68-86°F) may be used for degreening oranges. This treatment does not influence the internal quality (including soluble solids/acid ratio) and may accelerate deterioration and decay incidence.

Responses to Controlled Atmospheres (CA)
A combination of 5-10% O2 and 0-5% CO2 can be useful for delaying senescence and for firmness retention but does not have a significant effect on decay incidence and severity, which is the limiting factor to long-term storage of oranges. Fungistatic levels (10-15%) of CO2 are not used because they may result in off-flavors due to accumulation of fermentative metabolites. Commercial use of CA on oranges during storage and transport is very limited.

Physiological Disorders
Chilling injury. Symptoms include pitting, brown staining, and increased decay incidence. Minimum safe temperature depends on cultivar, production area, and maturity-ripeness stage at harvest. Severity of symptoms can be reduced if water loss is minimized (by waxing or film wrapping) and if decay-causing fungi are controlled (by use of fungicides and/or biological antagonists).

Stem-end rind breakdown. Symptoms include shriveling and peel injury around the stem due to aging.

Rind staining. This disorder results from overmaturity at harvest. It can be reduced by preharvest application of gibberellic acid that delays senescence.

Oil spotting (Oleocellosis). Harvesting and handling turgid oranges can result in release of oil that damages surrounding tissues. Thus, oranges should not be harvested when fully turgid such as early in the morning and soon after rain or irrigation.

Pathological Disorders
Important Diseases:

  • Green mold (Penicillium digitatum)
  • Blue mold (Penicillium italicum)
  • Phomopsis stem-end rot (Phomopsis citri)
  • Stem end rot (Lasiodiplodia theobromae)
  • Brown rot (Phytophthora citrophthora)
  • Sour rot (Geotrichum candidum)

Control Strategies:

  • Minimizing physical damage during harvesting and handling.
  • Treatment with postharvest fungicides and/or biological antagonists. Also, heat treatments may be used.
  • Prompt cooling and subsequent maintenance of optimum temperature and relative humidity throughout marketing operations.
  • Removal and/or exclusion of ethylene.
  • Effective sanitation procedures throughout postharvest handling.

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/orange.html updated July 5, 2000

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