Quercetin 3-O-beta-glucoside is better absorbed than other quercetin formsand is not present in rat plasma

The effect of the nature of the sugar moiety on quercetin absorption has be en investigated in rats. Four groups of rats received an experimental meal containing 20 mg of quercetin equivalents, supplied as quercetin, quercetin 3-O-beta -glucoside, quercetin 3-O-beta -rhamnoside or rutin. Four hours a fter the meal, the metabolites identified in hydrolysed plasma were identic al in all groups (3'- and 4'-methylquercetin). However, the total concentra tion of metabolites was markedly different: 11.2+/-1.8, 2.5+/-2.0 and 33.2/-3.5 muM for the quercetin, rutin, and quercetin 3-glucoside meals respect ively. After quercetin 3-rhamnoside consumption, we failed to detect any me tabolites in the plasma. These data suggest that the 3-O-glucosylation impr oves the absorption of quercetin in the small intestine, whereas the bindin g of a rhamnose to the aglycone markedly depresses it. Additional experimen ts have shown that the higher plasma levels measured after quercetin 3-gluc oside meal compared to the quercetin meal were maintained throughout the 24 -hour period following the meal. Using a multi-electrode coulometric detect ion, together with suitable chromatographic conditions, we were able to dis tinguish between the conjugated and the glycosylated forms. Thus, we clearl y showed the absence of quercetin 3-O-beta -glucoside in the plasma from ra ts fed a diet containing this glucoside. This result suggests that querceti n 3-O-beta -glucoside is hydrolysed before or during its intestinal absorpt ion.