Abstract: Purpose: To study the antimutagenic effect and mechanism of water extract of tea and related components; to distinguish between desmutagenic dose effect relationship and bactericidal action; in order to discern their similarities or differences in antimutagenesis against direct mutagen(1- NP) and indirect mutagen(Trp- P- 1). Methods: Desmutagenic assay and modified Ames test with Salmonella typhimurim TA 98 were applied. Results: Both tea extract and polyphenols were desmutagenic active without bactericidal action, EGCG and TF were far better than the others; Tea extract was more powerful in antimutagenicity on indirect mutagen(Trp- P- 1) ＋S 9 than on direct mutagen(1- NP)- S 9(P<0.01). The mixture of tea extract and Trp- P- 1 was not mutagenized(without S 9), but was mutagenized with S 9 pre- incubation, and the mutagenic activity was highly related to tea extract inhibiting rate against 1- NP- S 9(r=- 0.969 4). Conclusion: Tea polyphenols can inhibit the formation of indirect mutagen precursors. As a suppressive agent it can also inhibit direct mutagens. Tea polyphenols can form unstable combinations or unsafe structures as they block some strong oxidative mutagens.

Key words: desmutagen, tea, catechins, trp- P- 1, 1- NPC