Effects of gamma irradiation on the biological activity of green tea byproduct extracts and a comparison with green tea leaf extracts

Abstract

Green tea byproduct extract powder, a major byproduct of the green tea industry, was prepared and investigated for its biological activities after a gamma-irradiation treatment for the purpose of a brightened color. The color, total phenolic contents, antioxidative activity, tyrosine inhibition activity, cancer cell proliferation inhibition effect, and antimutagenicity were measured and compared with those of a green tea leaf extract powder. Hunter L* values of the irradiated green leaf and byproduct extracts were increased in a comparison with the nonirradiated extracts. The contents of total phenolic compounds of the green tea leaf and byproduct extracts were 424.2 +/- 11.45 and 335.5 +/- 18.65 mg/g of sample, respectively. The 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity of the 20 ppm green tea leaf and byproduct extracts were 68.2% and 57.6%, respectively. Ferric-reducing ability of the samples showed similar results to the DPPH radical scavenging capacity. The samples showed an inhibition of tyrosine and also a cancer cell proliferation inhibition effect. Especially, the antimutagenicities of the byproduct extracts showed a strong inhibition effect (96.20% and 57.77%) on 3-amino-1,4-dimethyl-5H-pyrido[4,3-b]indole (Trp) and 2-nitrofluorene (NF), respectively. Results indicated that, although the biological activity of green tea byproduct extracts is less than that of green tea leaf extract, it may be a potential source of a functional ingredient. In addition, irradiation can be applied to improve the colour and biological activity of the material.