Changes in trans-resveratrol and other phenolic compounds in grape skin and seeds under low temperature storage after post-harvest UV-irradiation

Changes in the concentrations of traps-resveratrol (Res) and other phenolic compounds in the skin and seeds of red grape (Vitis vinifera x V. amurensis 'Beiquan') during low temperature storage (-1 degrees +/- 0.5 degrees C) after post-harvest UV-B and UV-C irradiation and incubation at room temperature (25 degrees C) were evaluated. No obvious changes in Res levels were observed in control and UV-B-irradiated grape skins after 14 d. A higher content of Res was recorded in UV-B-irradiated grape skins for only 7 d in cold storage, but the content was highest in UV-C-irradiated grape skins for the entire period (28 d) in cold storage. Total levels of anthocyanins in grape skins after either UV treatment were significantly higher than in controls during the first 7 d of storage, while only those in UV-B-treated skins were significantly higher than controls during the later period (from 21 - 28 d) of storage, due to sharp declines in levels of the five main anthocyanins in UV-C-treated grape skins. Total flavan-3-ol and flavonol contents remained constant in UV-B- and UV-C-treated grape skins during cold storage and did not differ from controls. Levels of Res in grape seeds remained constant and did not differ between UV treatments, or from controls, over 28 d of low temperature storage. However, the total flavan-3-ol and flavonol contents in control and UV-B-treated grape seeds declined from day-2 to day-28 of cold storage, while those of UV-C-treated grape seeds remained constant. Changes in catechin and epicatechin were responsible for the changes observed in total flavan-3-ols and flavonols during cold storage.