Enzymatic modification by tannase increases the antioxidant activity of green tea

Tea catechins were extracted from green tea leaves, and the effect of tannase-aided treatment on their antioxidative activity was then examined. Their antioxidant capacity was evaluated using assays for DPPH, superoxide anion, trolox-equivalent antioxidant capacity (TEAC), hydrogen peroxide and metal ion chelation. The results show that tannase-treated green tea has a higher antioxidant capacity than the untreated analog at a concentration of 200 ppm, with greater superoxide anion, hydrogen peroxide and 2,2-diphenyl-1-picrylhydrazyl (DPPH) scavenging effects (97%, 83% and 62%, respectively). At a concentration of 100 ppm, the tannase-treated green tea also had significantly higher TEAC antioxidant activity compared to the untreated tea (2.4% vs. 1.0%). Furthermore, at 150 ppm the chelating activity of the treated tea for Fe+2/Cu+2 ions was higher compared to the untreated green tea (42.6/33.5% vs. 14.6/ 7.6%, respectively). The viability of RAW 264.7 cells incubated with tannase-treated green tea for 144 h was higher compared to analogs incubated with untreated tea. Our results demonstrate that antioxidant activity in flavonoids varies, and that the presence of galloyl residues decreases the antioxidant activity of tea catechins. (C) 2007 Elsevier Ltd. All rights reserved.