酸化ストレスと食品抗酸化物質

Daily foods contain a variety of minor components which possess antioxidative activity, such as vitamin E and vitamin C. On the other hand, it has been well known that reactive oxygen species (ROS) generating in the body cause oxidative damages in the tissues and fluids, resulting in the generation and progress of life style-related diseases. Therefore, it should be expected that dietary antioxidants are well introduced to individual food-style from the viewpoint of disease prevention and health promotion. However, there are two important subjects to be clarified, that is, the mechanism by which they exert the antioxidant activity in vivo, and the site at which they act as antioxidants in vivo. We are interested in common components present in foodstuffs, in particular, carotenoids, flavonoids and phytic acid, and are challenging to solve these subjects by use of carotenoids and flavonoids. Here we will discuss the result of our recent studies on dietary flavonoids. We have claimed that flavonoids are interfacial antioxidants whose activities appear at the interface between lipid-phase and water-phase. Nevertheless, little is known on the absorption and metabolism of flavonoids from diet. We recently investigated the absorption and metabolic pathway of quercetin, a representative flavonoid in plant foods, using rats, humans and cultured cell derived from human digestive tract. The result shows that a part of quercetin is absorbed from digestive tract and exclusively accumulates as conjugated metabolites in blood plasma. The antioxidative activity of quercetin exhibited in blood plasma is likely to be originated from conjugated metabolites. It is therefore implied that metabolic products largely contribute to the physiological function of flavonoids, when flavonoids are ingested from daily foods.