Electron spin resonance (ESR) spectroscopic assessment of the contributionof quercetin and other flavonols to the antioxidant capacity of red wines

Health benefits of red wine have been ascribed in part to the antioxidant p roperties of quercetin and other flavonols. Red wines, however, contain man y other polyphenolic compounds with antioxidant potential. The present stud y has assessed the antioxidant capacity of seven red wines using electron s pin resonance spectrometry to measure their ability to donate hydrogen atom s to a stable Fremy's radical. Antioxidant capacity of the wines was strong ly related to the total phenol content (r = 0.872, P < 0.01) but less so to total flavonol content (r = 0.651, P < 0.10). The only flavonols detected in the wines by HPLC with post-column derivatisation were the aglycones and conjugated forms of quercetin and myricetin. These accounted for less than 2% of total phenolic content when expressed as gallic acid equivalents. Al though these flavonols showed marked ability to quench Fremy's radical, the y contributed less than 1.5% to the total antioxidant capacity of the wines . Consequently, quercetin is not a major antioxidant in red wine. The antio xidant activity of other polyphenols may be of greater importance in contri buting to the reputed health benefits of moderate wine consumption. (C) 199 9 Society of Chemical industry.