THE RELATIVE ANTIOXIDANT ACTIVITIES OF PLANT-DERIVED POLYPHENOLIC FLAVONOIDS

The relative antioxidant activities, against radicals generated in the aqueous phase, of a range of plant-derived polyphenolic flavonoids, c onstituents of fruit, vegetables, tea and wine, have been assessed. Th e results show that compounds such as quercetin and cyanidin, with 3', 4' dihydroxy substituents in the B ring and conjugation between the A and B rings, have antioxidant potentials four times that of Trolox, th e vitamin E analogue. Removing the ortho-dihydroxy substitution, as in kaempferol, or the potential for electron delocalisation by reducing the 2,3 double bond in the C ring, as in catechin and epicatechin, dec reases the antioxidant activity by more than 50%, but these structures are still more effective than a-tocopherol or ascorbate. The relative significance of the positions and extents of hydroxylation of the A a nd B rings to the total antioxidant activity of these plant polyphenol ics is demonstrated.