title: The relative antioxidant activities of plant-derived polyphenolic flavonoids.
abstract: The relative antioxidant activities, against radicals generated in the aqueous phase, of a range of plant-derived polyphenolic flavonoids, constituents of fruit, vegetables, tea and wine, have been assessed. The 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, the 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, decreases the antioxidant activity by more than 50%, but these structures are still more effective than alpha-tocopherol or ascorbate. The relative significance of the positions and extents of hydroxylation of the A and B rings to the total antioxidant activity of these plant polyphenolics is demonstrated.
authors.affiliation: Free Radical Research Group, UMDS-Guy's Hospital, London.
authors.forename: C A
authors.initials: CA
authors.lastname: Rice-Evans
authors.forename: N J
authors.initials: NJ
authors.lastname: Miller
authors.forename: P G
authors.initials: PG
authors.lastname: Bolwell
authors.forename: P M
authors.initials: PM
authors.lastname: Bramley
authors.forename: J B
authors.initials: JB
authors.lastname: Pridham
mesh_terms: D000872:Anthocyanins / Q000737:chemistry / Q000378:metabolism*; D000975:Antioxidants / Q000378:metabolism*; D002839:Chromans / Q000378:metabolism; D005419:Flavonoids / Q000737:chemistry / Q000378:metabolism*; D006861:Hydrogen Peroxide / Q000378:metabolism; D007529:Isoflavones / Q000378:metabolism; D009211:Myoglobin / Q000378:metabolism; D010944:Plants; D013053:Spectrophotometry
chemical_list: D000872:Anthocyanins; D000975:Antioxidants; D002839:Chromans; D005419:Flavonoids; D007529:Isoflavones; D009211:Myoglobin; D006861:Hydrogen Peroxide; C010643:6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid