Antioxidant activity of quercetin

Zhang, Y., Yang, Y., Tang, K., Hu, X., Zou, G. (2008). Physicochemical characterization and antioxidant activity of quercetin-loaded chitosan nanoparticles. Journal of Applied Polymer Science, 107, 891-897. 

Flavonones and flavanonol are other heterocyclic pigments found in wine. Taxifolin 41 (2,3-dihydroquercetin) has only 50% of the antioxidative activity of quercetin, but it is both less mutagen and toxic (09MI451,07MI1074) ... 

Further experiments were carried out comparing the relative protective action of quercetin, epicatechin, and chlorogenic acid. It was concluded that while the antioxidant activity of quercetin had a role to play in protection of the lens against oxidative damage, other mechanisms must also be contributing, since inhibition of opacification and Ca influx did not correlate with antioxidant activity, it was likely that protection... 

The olives themselves contain many phenolic compounds with antioxidant properties. Bouaziz et al. (2005) investigated the olive cultivar Chemlali from Tunisia. Oleuropein (7.14), a bitter glycoside esterified with a phenolic acid, was the major compound present. Phenolic monomers and twelve flavonoids were also identified. The antioxidant activity of the extract was evaluated. Acid hydrolysis of the extract enhanced its antioxidant activity. / -Hydroxyphenyl-cthanol (7.12) and quercetin (1.43) showed antioxidant activities similar to that of 2,6-di-fert-butyl-4-methyl phenol (7.15), a reference compound with known antioxidant properties. It was suggested that a hydroxyl group at the ortho-position on the flavonoid B ring could contribute to the antioxidant activity of the flavonoids. 

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... 

Trans-resveratrol (trans-3,5,4 -trihydroxystilbene) is a non-flavonoid polyphenol found in grapes, mulberries, and other food prod-ucts. It is responsible for the antioxidant activity of red wine. Intake of moderate amount of red wine has been found to reduce the risk of cardiovascular diseases. In addition to antioxidant activity, resveratrol could inhibit platelet aggregation, and showed anticancer activity. The phenoxyl radicals of resveratrol produced during oxidation by hydroxyl radicals, one-electron oxidants, and peroxyl radicals showed absorption maximum at 410 nm (Fig. I). Reports indicate that trans-resveratrol is a better radical scavenger than vitamins E and C and its activity is similar to that of the flavonoids epicatechin and quercetin. From the comparison of the spectral and kinetic properties of the transients derived from trans-resveratrol and its analogues, it could be concluded that in the neutral and acidic solutions, the para-hydroxy... 

In products with complex combinations of various types of flavonoids and other phenolic compounds, effort has been made to ascribe the antioxidant activity of the product to different classes of polyphenols. Frankel et al. (1995) studied 20 selected California wines and related the antioxidant activity to the polyphenolic components of the wines, rather than to resveratrol. Antioxidant activity was measured by the ability of the wines to inhibit copper-catalyzed oxidation of human LDL. The correlation coefficient between antioxidant activity and total phenolic components of the wines was r = 0.94. Individual phenolic compounds (gallic acid, catechin, myricetin, quercetin, caffeic acid, rutin, epicatechin, cyanidin, malvidin-3-glucoside) contributed to the antioxidant activity. The correlation coefficient for the compounds ranged from r = 0.92 to r = 0.38 in descending order. 

Inhibitory activity against a-amylase by flavonoids and anthocyanins has been reported (39). Herbs used in Nigerian traditional medicine for the treatment of diabetes mellitus are known to contain phenol compounds especially the flavonoid quercetin and the mechanism of their antidiadetic activity may be brought about by their amylase inhibiting activity and the antioxidant activity of the phenolic compounds. 

Although phospholipid bilayers are better mimics of biomembranes than are micelles, there are few reliable quantitative data on flavonoid antioxidant activities in lipid bilayers. Terao and coworkers compared the antioxidant efficiency of quercetin and catechins (epicatechin and epicatechin gallate) with that of a-Toc in egg yolk PC liposomes using initiation by the water-soluble initiator, ABAP, and analysis of hydroperoxide formation and antioxidant consumption by HPLC. Based on the length of the induction periods and the profile of suppressed hydroperoxide formation, they concluded that quercetin and the catechins were more efficient antioxidants than a-Toc in these bilayers. Apparently the unique behavior of a-Toc in bUayers is responsible for these results (vide supra). In hexane and alcohols solution during suppressed peroxidation of methyl linoleate, the relative antioxidant activities reversed so that the flavonoids were 5-20 times less active... 

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