Comparison of Antimutagenic Effect of Various Tea Extracts (Green, Oolong, Pouchong, and Black Tea).J Food Prot. 1994 Jan; 57(1):54-58.JF
The antimutagenic effects of various tea extracts prepared from nonfermented tea (green tea), semifermented tea (oolong tea and pouchong tea), and fermented tea (black tea) were investigated by Salmonella/microsome assay. No mutagenicity or toxicity in Salmonella typhimurium TA98 and TA100 was observed with any tea extract. The tea extracts markedly inhibited the mutagenicity of 2-amino-3-methylimidazo(4,5-f)quinoline, 3-amino-1,4-dimethyl-5H-pyridol(4,3-b)indole,2-amino-6-methyldipyrido(l,2-a:3',2'-d)imidazole, benzo[a]pyrene, and aflatoxin B1 toward S. typhimurium TA98 and TA100 in the presence of S9 mixture, especially those of oolong and pouchong teas inhibited over 90% mutagenicity of these five mutagens at the dosage of 1 mg per plate. Among four tea extracts, black tea exhibited the weakest inhibitory effect on mutagenicity of these five mutagens. The mutagenicity of 4-nitroquinoline-N-oxide, a direct mutagen, was not inhibited by black and oolong tea extracts to S. typhimurium TA98 in the absence of S9 mixture but was increased by the tea extracts at the dose of 1 mg per plate to S. typhimurium TA100. As the antimutagenic effect of semifermented tea was stronger than nonfermented and fermented teas, some antimutagenic substances might be formed during manufacturing processes of tea.