Resveratrol Glucosides are Important Components of Commercial Wines

Abstract

Using a direct-injection HPLC method with isocratic elution and UV detection, the isomers of free resveratrol and their glucosides (polydatin) have been assayed in nearly 700 commercial red wines from most of the world's areas of production. The highest concentrations of polydatin were found in wines from the Midi and Rhone Valley of France, Canada, Italy, Spain and Portugal, and South America. In the last three regions, the polydatin concentrations exceeded those of free resveratrol which were the lowest of all categories examined, suggesting that the high sugar content of warm climate grapes may favor the glycosylation of resveratrol. In nine regions, the concentration of cis-polydatin exceeded that of trans-polydatin, the reverse being the case in five, yet in all trans-resveratrol concentrations exceeded those of cis-resveratrol. There was only a weak negative correlation overall between polydatin and resveratrol concentrations when all wines were included in the analysis. The low values for both polydatin and resveratrol in Californian wines are consistent with the notion that, despite high sugar content, some grapes may fail to express resveratrol synthetic enzymes due to genetic characteristics or to lack of environmental stress, and consequently little of the free resveratrol is available for glycosylation. The influence of cultivar was examined in wines from several regions. Among wines from California, Australia, South America and Canada, highest polydatin concentrations were found respectively in those from Zinfandel, Shiraz, Merlot and Pinot noir. Wines from the Northern Rhone Valley (predominantly Shiraz) had lower concentrations than those from the Southern Rhone where Mourvedre, Grenache, Carignane and Cinsault predominate. The high polydatin and very low resveratrol concentrations of Vintage Ports highlight enological techniques, particularly duration of fermentation, as important modulating factors. The concentrations of polydatin present in most red wines are likely to add significantly to the presumed health benefits attributable to resveratrol.