Evolution of trans- and cis-resveratrol content in red grapes (Vitis vinifera L. cv Mencia, Albarello and Merenzao) during ripening

Concentrations of cis- and trans-resveratrol were analyzed in grapes from three red Galician varieties (Mencia, Albarello and Merenzao). Free resveratrol was quantified using a HPLC method (binary gradient) with fluorescence detection. The grapes were sampled weekly during the last 3 weeks before the optimal stage of maturation and the three parts were separated (skin, pulp and seed). These compounds are absent in pulp in all the grapes and the varieties, and the content in skin and seed varied according to the variety (Mencia > Albarello > Merenzao) and the vintage (1999 > 2001 > 2000). The results obtained from the grapes (7-24 mg/L) indicated that the wines elaborated from Mencia variety could be present with important amounts of trans-resveratrol.