Green Tea Research Today is a free monthly online journal that collates and summarizes the latest research about Green Tea, including details on benefits, antioxidants, weight loss, diet, side effects. | ||||||||
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Antioxidant and pro-oxidant effects of green tea extracts in oxygen radical absorbance capacity assay.Shin JK, Kim GN, Jang HD Department of Food and Nutrition, Hannam University, Daejeon, Republic of Korea. Green tea extracts (GTEs) [water (GTE-W) and 75% ethanol (GTE-E)] were investigated to characterize their propensities to act as antioxidants or as pro-oxidants by analyzing oxygen radical absorbance capacity (ORAC) and scavenging capacity for hydroxyl radical. When 2,2'-azobis(2-amidinopropane) dihydrochloride was used for the generation of peroxyl radicals, both GTE-W and GTE-E exhibited strong concentration-dependent scavenging activity through donating protons, which could be explained by their reducing property. When hydroxyl radicals were generated through the addition of Cu(2+) and H(2)O(2), GTE-W and GTE-E exhibited antioxidant activity or pro-oxidant activity, depending on their concentrations, which might be attributed to the metal chelating activity, the scavenging activity on hydroxyl radical, and/or the pro-oxidant activity to generate some reactive oxygen species. When Cu(2+) without H(2)O(2) was used as an oxidant in the assay, the copper-initiated pro-oxidant activities of GTE-W and GTE-W was consistent with the availability of (-)-epigallocatechin and (-)-epicatechin to generate hydrogen peroxide and/or hydroxyl radical. The pro-oxidant activity of GTE-W and GTE-E was demonstrated by the deoxyribose assay. These results indicate that both GTE-W and GTE-E can have pro-oxidant activity at lower concentrations and antioxidant activity at higher concentrations in the ORAC and deoxyribose assays using generated hydroxyl radicals. Published 2 May 2007 in J Med Food, 10(1): 32-40.
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