Sunlight exposure increases the phenolic content in postharvested white grapes. An evaluation of their antioxidant activity in Saccharomyces cerevisiae

Sunlight exposure is a traditional way to dry postharvested white Pedro Ximenez grapes, and the dried grapes are the basis of a sweet fortified wine elaborated in the South of Spain. In this paper, we have studied the effect of seven days of exposure of grapes to sunlight. The phenolic content in the skins and flesh has been determined. The transient induction of phenolics has been detected and identified in skins by HPLC and MS/MS. Maximum induction was after 2 days exposure with an increase in the levels of quercetin-3-O-glucoside, engeletin (dihydrokaempferol-3-O-rhamnoside) and astilbin (taxifolin 3-O-rhamnoside). We have evaluated the antioxidant and protective effects of the phenolic extracts of these grapes in Saccharomyces cerevisiae after exposure to H2O2. Phenolic extracts reduced the basal intracellular level of peroxides in a concentration dependent manner. There was a corresponding significant reduction in carbonylated proteins in treated and control cells and increased survival of yeast cells exposed to H2O2. Our results indicate that sundried grapes display a high antioxidant capacity resulting in a decrease in the oxidative cellular environment.