Antioxidant activity of tea

Chemical Antioxidant Systems. The antioxidant activity of tea extracts and tea polyphenols have been determined using in vitro model systems which are based on hydroxyl-, peroxyl-, superoxide-, hydrogen peroxide-, and oxygen-induced oxidation reactions (109—113). The effectiveness of purified tea polyphenols and cmde tea extracts as antioxidants against the autoxidation of fats has been studied using the standard Rancimat system, an assay based on air oxidation of fats or oils. A direct correlation between the antioxidant index of a tea extract and the concentration of epigallocatechin gallate in the extract was found (107). 

The total antioxidant activity of teas and tea polyphenols in aqueous phase oxidation reactions has been deterrnined using an assay based on oxidation of 2,2 -azinobis-(3-ethylbenzothiazoline-sulfonate) (ABTS) by peroxyl radicals (114—117). Black and green tea extracts (2500 ppm) were found to be 8—12 times more effective antioxidants than a 1-mAf solution of the water-soluble form of vitamin E, Trolox. The most potent antioxidants of the tea flavonoids were found to be epicatechin gallate and epigallocatechin gallate. A 1-mAf solution of these flavanols were found respectively to be 4.9 and 4.8 times more potent than a 1-mAf solution of Trolox in scavenging an ABT radical cation. 

KUMAMOTO M and soNDA T (1998) Evaluation of the antioxidative activity of tea by an oxygen electrode method , Biosci Biotechnol Biochem, 62, 175-7. 

MATSuzAKi T and KARA Y (1985) Antioxidative activity of tea leaf catechins , JAgric Chem Soc Jpn, 59, 129-34. 

WANG s M and zhao j f (1997) Antioxidant activities of tea polyphenol on edible oils . Western Cereal and Oil Technology, 11, 44-6. 

HUANG s w and frankel e n (1997) Antioxidant activity of tea catechins in different lipid systems, J Agric Food Chem, 45, 3033-8. 

Frei B, Higdon JY. 2003. Antioxidant activity of tea polyphenols in vivo Evidence from animal studies. J Nutr 133 3275S-3284S. 

C. Rice-Evans, Methods to quantify antioxidant activity of tea/tea extracts in vitro, Crit. Rev. FoodNutr., 2001, 41, 405 107. 

The inhibitory effects of tea polyphenols on xanthine oxidase (XO) were investigated. Theaflavins and EGCG inhibit XO to produce uric acid and also act as scavengers of superoxide. Theaflavin 3,3 -digaUate (TE-3) acts as a competitive inhibitor and is the most potent inhibitor of XO among these compounds. TE-3 also inhibited the superoxide production in HL-60 cells. Therefore, the antioxidative activity of tea polyphenols is due not only to their ability to scavenge superoxides but also to their ability to block XO and relative oxidative signal transducers. ... 

Figure 9.16. Antioxidant activity of tea catechins in (a) bulk com oil and (b) com oil-in-water emulsion. Huang and Frankel (1997), with permission from the American Oil Chemists Society. See structures and abbreviations in Figure 9.15.

Antioxidant activity of teas [Fe(TPTZ)J3+ Spectrophotometric Merging zone Martins et al. (2013)... 

Martins, A. C., L. Bukman, A. M. M. Vargas et al. 2013. The antioxidant activity of teas measured by the FRAP method adapted to the FIA system Optimizing the conditions using the response surface methodology. Food Chem. 138 574-580. 

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