The best-known group of polyphenolic compounds is flavonoids, belonging to secondary plant metabolites. Rich sources are flowers and leaves, where they can be found in the superficial layers of tissues give them intense color, while protecting against UV radiation. Other common sources are fruits, especially grapes and citrus,
vegetables, seeds, legumes, and green tea55. Almost all flavonoids have biological activity. Antioxidant capacities are possible through different mechanisms of action. Direct mechanisms are based on the capture of free radicals and limiting
their arrangement in cells by inhibiting the activity of enzymes that participate in the formation of reactive oxygen species. Indirect antioxidant action involves interupting the cascade of reactions of free radicals and the chelation of metal ions,which prevents reactive hydroxyl radicals in cells. Compounds from the group of flavonoids
having significance in photoprotection are genistein,silymarin, equol and quercetin.