Mutagenicity and antimutagenic effect of soymilk fermented with lactic acid bacteria and bifidobacteria

In this study, soymilk was first fermented with lactic acid bacteria (Streptococcus thermophilus, Lactobacillus acidophilus) and bifidobacteria (Bifidobacterium infantis, Bifidobacterium longum) both individually and simultaneously. Mutagenicity and the suppression of fermented soymilk against the mutagenesis induced by 4-nitroquinoline-N-oxide (4-NQO), a direct-acting mutagen, and 3,2'-dimethyl-4-amino-biphenyl (DMAB), an indirect-acting mutagen, on Salmonella typhimurium TA 100, was then investigated. It was found that the fermented soymilk shows no mutagenic activity on Sal. typhimurium TA 100. Fermentation, in general, significantly (p<0.05) enhanced the antimutagenicity of soymilk. The levels of increased antimutagenicity of fermented soymilk varied with the starter organism and the type of mutagen tested. Although unfermented soymilk exerted lower antimutagenic activity against DMAB than 4-NQO, the fermented soymilk, generally, showed a higher antimutagenic activity against DMAB than 4-NQO. Among the various fermented soymilk tested, soymilk fermented with both Str. themophilus and B. infantis simultaneously exhibited the highest antimutagenicity of 85.07% and 85.78%, respectively, against 4-NQO and DMAB Further investigation on this fermented soymilk revealed that both the antimutagenic factors formed during fermentation and the cells of the starter organisms contributed to the increased antimutagenic activity against DMAB, while the former led to the increased activity against 4-NQO.