Two types of antimutagenic effects of gallic and tannic acids towards N-nitroso-compounds-induced mutagenicity in the Ames Salmonella assay.

The frequency of his+ revertants induced by N-methyl-N-nitrosourea (MNU) and N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) in the strain TA100 of Salmonella typhimurium was decreased by gallic and tannic acid. In weak buffer solutions, the inhibition effects of gallic acid towards MNU and MNNG mutagenicity was caused primarily by a decrease of pH in the incubation mixtures. At adjusted pH (pH 5.0 and 6.5), the antimutagenic effects are largely the result of an interaction between MNU or MNNG with phenolic acids outside the cells.