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Quercetin is an important dietary flavonoid with putative beneficial effects in the prevention of cancer and CVD. The in vivo bioactivity of quercetin depends on its bioavailability, which varies widely between foods. We used an in situ rat intestinal perfusion model to study whether differential small intestinal hydrolysis of the sugar moiety of five naturally occurring quercetin glycosides determines the small intestinal uptake and subsequent biliary excretion of quercetin. After 30 min perfusion, a decrease of intact quercetin glycoside in perfusate was observed for quercetin-3-O-ß-glucoside (20·9 (sem 1·4) μmol/l) and quercetin-4′-O-ß-glucoside (23·5 (sem 1·6) μmol/l), but not of quercetin-3-O-ß-galactoside, quercetin-3-O-ß-rhamnoside and quercetin-3-O-α-arabinopyranoside. Appearance of free quercetin in perfusate and conjugated quercetin metabolites (quercetin, isorhamnetin, and tamarixetin) in portal and …