Flavonoids and other plant phenols in the diet: Their significance as antioxidants

Phenols are universal components of plant material. Flavonoids are polyphenolic constituents of the diet with antioxidant properties by virtue of the structural arrangements and hydrogen-donating potential of their phenolic groups. The ability of specific phenolics to chelate transition metal ions is also of significance. In vitro , the antioxidant activity of the aglycone forms of these polyphenols is, in the main, greater than that of vitamin E and vitamin C. In the diet they are present principally as glycosylated, esterified or polymerized derivatives. Many factors, such as the extent of their gastrointestinal absorption, metabolism (possibly into derivatives with enhanced activity) and interaction with target cells, affect the bioavailability and activity of dietary polyphenols. The balance between beneficial and detrimental effects after their consumption is thus somewhat unpredictable. The possible sites at which these compounds might act as significant dietary micronutrient antioxidants are: (1) i...