Changes in grapevine berry skin photochemistry may support metabolic responses to postharvest treatment by ultraviolet light

Harvested mature berry clusters of two white table grape cultivars were used to study the effects of postharvest UV irradiation. One cultivar, 'Queen of Vineyard' (QV), had higher light-acclimated PSII quantum yield, higher phenolic contents, and stronger total antioxidant capacities than the other, 'White Sultana' (WS). These differences were maintained throughout the experiment. Responses of the two cultivars to a 30-min UV irradiation were also different. Antioxidant capacities and flavonol, especially quercetin-3-O-glucuronide, contents were lower 2 h after the UV treatment in both cultivars and recovered in QV but not in WS berry skins later on. Our data demonstrate that mature grapevine berries have photosynthetically active tissues capable of dynamic changes even several hours after harvest and suggest that changes in photochemistry may contribute to postharvest metabolic responses of berry skins. Results also support the potential of postharvest manipulation of fruit qualities with UV irradiation.