Postharvest Handling and Storage of Berries
Berries are very perishable and maintaining fresh quality after harvest depends on proper handling, transportation, and storage.
Maturity and Quality Indices
Harvest date is determined by berry surface color. Most standards require more than ½ to � of the berry surface to be colored, depending on the grade and berry type. All berries should be harvested near ripe, as eating quality does not improve after harvest. Appearance (color, size, shape, and freedom from defects), firmness, flavor (soluble solids, titratable acidity, and flavor volatiles), and nutritional value (vitamin C) are all important quality characteristics. For acceptable flavor, a minimum of 7% soluble solids and/or a maximum of 0.8% titratable acidity are recommended.
Ethylene Production and Responses
Strawberries produce very little ethylene, <0.1 ppm per kg per hour at 20°C. Other berries produce between 0.1 and 1.0 ppm per kg per hour at 20°C.
Ethylene does not stimulate the ripening of strawberries, raspberries, and blackberries. Therefore, these berries should be harvested near to full ripe. Blueberries are climacteric fruit and will respond to ethylene. However, blueberries should also be harvested near to full ripe because flavor does not improve after harvest. Removal of ethylene from storage air may reduce disease development in all berries.
Cooling and Storage Conditions
Precooling (rapid removal of field heat) is essential within 1‑2 hours of harvest. For example, strawberries maintained at 10°C have about one-third the storage life as those rapidly cooled down to 0°C. Precooling may be accomplished by forcing rapidly moving cold air through stacks of berries (forced-air cooling).
Optimum storage conditions for strawberries (7‑10 days), blueberries (2‑4 weeks), raspberries and blackberries (2‑5 days) are 0°C and 90‑95% relative humidity. Cranberries (2‑4 months) are chilling sensitive and therefore, should be stored at 3°C. In general, storage-life is very dependent on the handling of berries during and after harvest.
The highest freezing point is ‑0.8°C for strawberries and blackberries, ‑0.9°C for cranberries, ‑1.1°C for raspberries, and ‑1.3°C for blueberries. Overall, berries with high soluble solids content are less likely to freeze.
Modified atmosphere (MA) packaging for shipment with 15-20% carbon dioxide and 5-10% oxygen reduces the growth of Botrytis cinerea (grey mold rot) and other decay causing organisms. In addition, it reduces the respiration and softening rates of berries, thereby extending postharvest life. Whole pallet covers and consumer packages for containment of the modified atmosphere are commonly used.
Shriveling / Water Loss. Berries are very susceptible to water loss, which results in fruit shriveling and loss of gloss. The maximum permissible amount of water that can be lost (based on weight loss) from raspberries and blackberries before becoming unmarketable is 6%.
MA-Related Disorders. Exposure of berries to <2% oxygen and/or > 25% carbon dioxide can cause off-flavors and brown discoloration, depending on berry and cultivar, duration of exposure, and temperature.
Chilling Injury of Cranberries. Chilling injury can develop in cranberries stored at temperatures below 3°C. Symptoms include dull appearance, rubbery texture, and increased susceptibility to decay.
Diseases are the greatest cause of postharvest losses in berries. Prompt cooling, storage at the lowest safe temperature, preventing physical injury to the fruit, and shipment under high carbon dioxide (10-15%) are the best methods for disease control. In addition, care should be taken to keep diseased or wounded berries out of packages, as rot can spread from diseased to nearby healthy berries.
Gray mold (Botrytis cinerea) can be a serious problem in berries. This disease can develop during storage if fruit has been contaminated though harvest and handling wounds. Avoiding mechanical injuries and good temperature management are effective control measures. This fungus continues to grow at 0oC, albeit growth is very slow at this temperature.
Rhizopus rot (Rhizopus stolonifer) can also be a problem in berries. This fungus forms a fluffy, black whiskery mold on the fruit surface. Cooling the berries and keeping them below 5°C is very effective against this fungus, since it will not grow at these temperatures.
Lidster, P.D., P.D. Hildebrand, L.S. B�rard, and S.W. Porritt. 1988. Commercial storage of fruits and vegetables. Agriculture Canada Publication 1532/E.
Mitcham, E.J., C.H. Crisosto, and A.A. Kader. 2000. Strawberry: Recommendations for maintaining postharvest quality. University of California, Davis.
Mitcham, E.J., C.H. Crisosto, and A.A. Kader. 2000. Bushberry: Recommendations for maintaining postharvest quality. University of California, Davis.
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