Effect of water quality on the nutritional components and antioxidant activity of green tea extracts

Green tea extracts (GTEs) were prepared with tap water (TW), activated carbon adsorbed water (AC), deionized water (DI), distilled water (DW), reverse osmosis water (RO) and ultra-pure water (UP). Their nutritional components were determined by chemical methods. Deoxyribose assay and the xanthine oxidase method were applied to test the antioxidant activities of GTE in vitro. The results indicated that there were statistically significant differences (P < 0.05) in the yield rate, the contents of polyphenols, catechins, caffeine, copper, lead and fluorine. Among them, DI gave the greatest yield rate and polyphenols, with low caffeine, DW increased the contents of non-ester catechins and AC enhanced the concentrations of ester catechins. The contents of copper and lead in GTEs were highly correlated with those of the tested water (r = 0.767 and 0.871, respectively). Fluorine contents in all GTEs were above 6.0 g kg−1. GTEs prepared with RO displayed the highest antioxidant activities among the six GTEs.