Concentrations of Selected Polyphenols in White Commercial Wines

Abstract

Using an HPLC method with diode array detection, we have measured the concentrations of flavan 3-ols (catechin and epicatechin), trihydroxystilbenes (the cis and trans isomers of polydatin and resveratrol), flavonols (quercetin and rutin), and the hydroxy acid p-coumaric in 644 white wines from the major wine-producing regions. Quercetin and rutin were detectable in very few of these wines, and the latter could not be unequivocally distinguished from isoquercitrin, which was not specifically measured in this study. One or more of the hydroxystilbenes were measurable in most, but the cis isomers of polydatin and resveratrol were not frequently detectable. Among Chardonnay wines, those from Australia had the highest concentrations of both flavan 3-ols, while those from California were highest in p-coumaric acid and trans-resveratrol. For Sauvignon blanc wines, those of South Africa had the highest content of both flavan 3-ols. For Riesling wines, those from France (Alsace) were highest in (+)-catechin and trans-resveratrol, German wines in (-)-epicatechin, and Canadian wines in trans-polydatin. French wines from Pinot (blanc and gris) were higher in all constituents than North American, while Italian wines from this cultivar were the lowest. There were no significant differences in polyphenol concentrations between Gewürztraminer wines from France and North America. Low concentrations of polyphenols were found in miscellaneous white wines from Central Europe and Italy. When analyzed by cultivar rather than by region, highest flavan 3-ol concentrations were observed in wines from French hybrid grapes (Vidal blanc and Seyval blanc) and lowest in Gewürztraminer, whereas the former had lowest concentrations of p-coumaric acid and trihydroxystilbenes. In all instances, the concentrations of the polyphenols measured in white wines were 5% to 25% those of red wines (with quercetin and cis-trihydroxystilbenes being undetectable in most) and do not explain why white wines may have the same potency as red wines in certain biological functions. Climatic factors that appear to modulate polyphenol concentrations in red wines such as stress, fungal pressure and sunlight do not seem to be important for white wines. The intrinsic properties of the individual cultivars or clones together with regional differences in enological techniques may be the most important factors.