Effects of pH on antioxidant and antimicrobial properties of tea saponins

In order to study the effects of environmental conditions, antioxidant and antimicrobial activities of tea saponins (TS) in different pH values were evaluated. The antioxidant activity was examined by reducing power, superoxidant radical scavenging activity, metal chelating activity and so on. Antimicrobial activity was investigated using gram-negative, gram-positive bacterial and fungi. In vitro antioxidant activities exhibited pH dependency, and increased with increasing concentration of the extract. When pH was 8.0, TSs showed the best antioxidant activities, while the reversal result was found in antimicrobial measurement. At pH 8.0 and concentration 2.0 mg/mL, TSs scavenged 90.5% of superoxide radical. At pH 4.8, the minimum inhibitory concentration of TS was lower than 0.00625 % (w/v). The results indicate that TS can be an ideal antioxidant, and its antioxidant and antimicrobial activity depend on pH values.