Vegetables contain a variety of flavonoids, such as flavonols, flavones and anthocyanidins. Numerous in vitro studies have revealed diverse biochemical actions of flavonoids, and their antioxidant activity should be, at least partly, responsible for these actions. We are interested in quercetin (3, 3', 4', 5, 7-pentahydroxyflavone), a flavonol-type flavonoid as an anti-atherosclerotic food factor and have examined its bioavailability to evaluate the biological effect. Quercetin and other flavonoids frequently exist as their glycoside forms in vegetables. Glucoside-bound quercetin is absorbed and hydrolyzed in small intestine through glucose-transport system or passive transport after lactase phlorizin hydrolase (LPH)-dependent deglucosidation. Quercetin glycosides other than glucoside forms are likely to be absorbed in large intestine after hydrolysis with enterobacteria. Efficiency of the absorption is considerably affected by the coexisting food components. Lipids and emulsifiers were found to enhance the absorption. In any cases, resulting quercetin aglycone is converted to conjugated glucuronides and/or sulfates during the process of their absorption. Some metabolites circulating in the blood stream can act as free radical scavengers, as well as the inhibitors of lipoxygenase and xanthine oxidase. It is therefore likely that biological effect of quercetin is originated from conjugated metabolites. Metabolic conversion of flavonoids to their conjugates may be a process for regulating their action on cellular oxidative stress.

抄録全体を表示