Biological and anti-microbial activity of irradiated green tea polyphenols

Polyphenols of green tea leaf were separated and irradiated at 40 kGy to investigate the effect of irradiation on changes of biological and anti-microbial activities. The major antioxidative activities, including electron donating, inhibition of xanthine oxidase, metal ion chelating, and inhibition of lipid oxidation were maintained through irradiation, except for superoxide dismutase (SOD)-like activity at the 200 ppm level. The anti-microbial activities against Staphylococcus aureus and Streptococcus mutans were higher in the irradiated sample, which showed inhibition of microorganisms tested at a lower concentration than those of the non-irradiated sample. Ranges of the inhibition zone for growth of Escherichia coli, S. aureus, S. epidermidis and S. mutans, at 1 mg/disc, were 9.3, 10.1, 22.5 and 9.3 mm in non-irradiated control but 10.8, 11.0, 25.0, and 11.7 mm in irradiated samples, respectively. Results indicated that irradiation of polyphenols, the major bioactive compounds in green tea, may maintain the biological activities and even increase the anti-microbial activity. The results also demonstrated that irradiation of green tea polyphenols, for removal of dark colour, may be applicable in the food or cosmetic industries.