Effect of postharvest ultraviolet irradiation on resveratrol and other phenolics of cv. Napoleon table grapes

In the skin of cv. Napoleon table grapes, the anthocyanins malvidin 3-gluco side (and its acetyl and p-coumaroyl derivatives), cyanidin 3-glucoside, pe onidin 3-glucoside, cyanidin 3-glucoside, petunidin 3-glucoside, and delphi nidin 3-glucoside were identified by HPLC-DAD-MS. In addition, quercetin 3- glucoside and 3-glucuronide, caffeoyltartaric, piceid, and resveratrol were also detected. The content of most phenolics remained quite constant durin g postharvest refrigerated storage (10 days at 0 degreesC) while the resver atrol derivatives increased 2-fold. Postharvest treatments of grapes with U VC and UVB light induced a large increase in resveratrol derivatives (3- an d 2-fold, respectively). This means that a serving of mature Napoleon grape s (200 g) provides similar to1 mg of resveratrol, which is in the range of the amount supplied by a glass of red wine. This can be increased to 2 or 3 mg of resveratrol per serving in grapes that have been irradiated with UVB or WC, respectively. These results show that refrigerated storage and UV i rradiation of table grapes can be beneficial in terms of increasing the con tent of potentially health-promoting phenolics.