Postharvest responses to high fruit temperatures in the field

The impact on postharvest responses, of preharvest exposure of fruit and ve getables to direct sunlight, with associated high tissue temperatures, is r eviewed. Fruit and vegetable flesh temperatures well above 40 degreesC have been recorded in direct sunlight in a wide range of crops in both hot and temperate climates. These high temperatures, both in terms of diurnal fluct uations and long-term exposure, can result in differences in internal quali ty properties such as sugar contents, tissue firmness, and oil levels, as w ell as in mineral content differences. Fruit with different temperature his tories will also respond differently to postharvest low temperatures and he at treatments used for insect disinfestation. For example, avocado fruit fr om exposed sites on a tree have less chilling injury, whereas more chilling damage is found in exposed tissues of citrus and persimmons. Mechanisms of high temperature effects on postharvest responses are discussed, including the role of heat shock proteins, membrane damage, and skin characteristics . Differences in exposure of fruit on the tree may be responsible for much of the wide variation commonly found in fruit with regard to at-harvest qua lity, ripening and postharvest behaviour. (C) 2000 Elsevier Science B.V. Al l rights reserved.