title: Antioxidant and pro-oxidant effects of green tea extracts in oxygen radical absorbance capacity assay.
abstract: 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.
authors.affiliation: Department of Food and Nutrition, Hannam University, Daejeon, Republic of Korea.
authors.forename: Jung-Keun
authors.initials: JK
authors.lastname: Shin
authors.forename: Gyo-Nam
authors.initials: GN
authors.lastname: Kim
authors.forename: Hae-Dong
authors.initials: HD
authors.lastname: Jang
mesh_terms: D000975:Antioxidants / Q000494:pharmacology*; D002392:Catechin / Q000032:analysis; D004249:DNA Damage / Q000187:drug effects; D016166:Free Radical Scavengers / Q000494:pharmacology; D017665:Hydroxyl Radical; D007502:Iron Chelating Agents / Q000494:pharmacology; D016877:Oxidants / Q000494:pharmacology*; D010084:Oxidation-Reduction; D010636:Phenols / Q000032:analysis; D017382:Reactive Oxygen Species / Q000737:chemistry*; D013662:Tea / Q000737:chemistry*
chemical_list: D000975:Antioxidants; D016166:Free Radical Scavengers; D007502:Iron Chelating Agents; D016877:Oxidants; D010636:Phenols; D017382:Reactive Oxygen Species; D013662:Tea; D017665:Hydroxyl Radical; D002392:Catechin