Antioxidant activity of flavonoids

Antioxidant activity of flavonoids has already been shown about 40 years ago [90,91]. (Early data on antioxidant flavonoid activity are cited in Ref. [92].) Flavonoids are polyphenols, and therefore, their antioxidant activity depends on the reactivity of hydroxyl substituents in hydrogen atom abstraction reactions. As in the case of vitamins E and C, the most studied (and most important) reactions are the reactions with peroxyl radicals [14], hydroxyl radicals [15], and superoxide [16]. 

Miyake, Y. et al., Isolation of C-glucosylflavone from lemon peel and antioxidative activity of flavonoid compounds in lemon fruit, J. Agric. Food Ghem., 45, 4619, 1997. 

Rios, J.L. et al., Antioxidant activity of flavonoids from Sideritis javalambrensis, Phytochemistry, 31, 1947, 1992. 

In general, optimal antioxidant activity of flavonoid is associated with the presence of multiple phenolic groups (hydroxyl groups increase the antioxidant activity, whereas methoxy groups suppress it), a carbonyl group at C-4, and free C3 and C5 hydroxyl groups. All these structural features are summarised in Fig. (2). 

Amic D, Davidovic-Amic D, Beslo D, Rastija V, Lucic B, Trinajstic N. 2007. SAR and QSAR of the antioxidant activity of flavonoids. Curr Med Chem 14 827-845. 

Rice-Evans C, Miller NJ. 1996. Antioxidant activities of flavonoids as bioactive components of foods. Biochem Soc Transac 24 790-795. 

The antioxidant activity of flavonoids in liposomes has also been extensively studied. Gordon and Roedig-Penman [93] used liposomes formed from egg PC to compare the antioxidant potencies of myricetin (31) and quercetin... 

M22. Miyake, Y., Shimoi, K., Kumazawa, S., Yamamoto, K., Kinae, N., and Osawa, T., Identification and antioxidant activity of flavonoid metabolites in plasma and urine of eriocitrin-treated rats. 

Torel, J., Cillard, J., and Cillard, P. 1986. Antioxidant activity of flavonoids and reactivity with peroxy radicals. Phytochemistry 25, 383 -385. 

RICE-EVANS, C.A., MILLER, N.J., Antioxidant activity of flavonoids as bioactive compounds. Biochem. Soc. Trans., 1996, 24, 790-794. 

The position and the degree of hydroxylation (especially at the A and B rings) are of primary importance in determining the antioxidant activity of flavonoids. Dihydroxylation at ortho position of the B ring contributes to antioxidant activity however, para and meta hydroxylation of the B ring do not occur naturally. All flavonoids with 3, 4 -dihydroxy configuration possess antioxidant activity (18, 147). 

ANTIOXIDANT ACTIVITY OF FLAVONOIDS Free Radical Scavenging Activity... 

These results are in agreement with the structure-activity relationship proposed by Bors et al., who used pulse radiolysis to study the antioxidant activity of flavonoids [116-118]. 

Fig. (5). Structural criteria that enhances the antioxidant activity of flavonoids. 1,11, III Structural groups proposed by Bor et al [137,138,157], IV Structural group proposed by Arora et al [148],...

Antioxidant activity of flavonoids and in non-processed foodstuff which are present has been extensively studied [13, 29, 155, 160, 161,... 

Torel J, Cillard J, Cillard P. Antioxidant activities of flavonoids and reactivity with peroxy radical. Phytochemistry 1986 25 383-385. 

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