Determinations of the antimutagenic activities of several probiotic bifidobacteria under acidic and bile conditions against benzo[a]pyrene by a modified Ames test

Antimutagenic activities of six bifidobacteria, after acidic and bile treatment mimicking gastrointestinal conditions, against benzo[a]pyrene (B[a]P) were determined by a modified Ames test using Salmonella typhimurium TA 100. Results showed that when bifidobacteria were treated at pH 2.0 for 3 h or 1% bile for 6 h, their antimutagenic activities against B[a]P were increased as compared to controls at pH 7.0 for 0 h. After sequential acidic pH and bile treatments, Bifidobacterium lactis Bb-12 displayed the highest antimutagenic activity (71.5%), although its viable cell number was less than 2.0 log cfu/ml. The antimutagenic activity of B. lactis Bb-12 against B[a]P was increased as pH values were increased from 2.0 to 7.0, and reaction time was extended from 1 to 3 h. However, antimutagenic activity was decreased as bile salt concentration was increased from 0.5% to 2.0%. The antimutagenic activity of B. lactis Bb-12 against B[a]P was increased in the presence of whole milk (WM), semiskimmed milk (SSM) and skimmed milk (SM). When B. lactis Bb-12 was preincubated with B[a]P and milk substrates, its antimutagenic activity was increased to 99–100%.