Chilling and Freezing Injury

Chien Yi Wang
Produce Quality and Safety Laboratory, USDA, ARS
Henry A. Wallace Beltsville Agricultural Research Center, Beltsville, MD

Chilling Injury: Many fruits, vegetables, and ornamentals of tropical or subtropical origin are sensitive to low temperatures (Paull, 1990). These crops are injured after a period of exposure to chilling temperatures below 10 to 15 °C (50 to 59 °F) but above their freezing points (Lyons, 1973; Wang, 1990). Certain horticultural crops of temperate origin are also susceptible to chilling injury (Bramlage and Meir, 1990). Those temperate crops, in general, have lower threshold temperatures, < 5 °C (41 °F). At these chilling temperatures, the tissues weaken because they are unable to carry on normal metabolic processes. Various physiological and biochemical alterations and cellular dysfunctions occur in chilling-sensitive species in response to chilling stress
...........

Freezing Injury: The recommended storage temperatures for commodities that are not susceptible to chilling injury are as low as possible but slightly above the freezing point. Freezing injury occurs when ice crystals form in the tissues.. Cultivars, locations, and growing conditions may affect the freezing point. To be on the safe side, the highest temperature at which freezing of a specific commodity may occur should be used as a guide for recommending the optimum storage temperature. More detailed discussion of freezing points and factors affecting them can be found in McColloch (1953), Whiteman (1957), and Parsons and Day (1970; 1971). The most common symptom of freezing injury is a water soaked appearance. Tissues injured by freezing generally lose rigidity and become mushy upon thawing.
.........


Dosya Türü : pdf
Şifre : www.forumfood.net