Antimutagenic activity of milk fermented by Streptococcus thermophilus and Lactobacillus bulgaricus

Antimutagenic activity of acetone or ethylacetate extracts of skim milk fermented by Streptococcus thermophilus, Lactobacillus bulgaricus, or a combination of both the organisms was studied using Salmonella typhimurium (TA 98 and TA 100). Mutagens used were 4-nitroquinoline-N-oxide (a direct-acting mutagen) and 2-aminofluorene (a mutagen requiring S9 activation). Extracts from all fermented milks showed significant (P less than .05) dose response in suppressing the number of revertants caused by NQNO and 2-aminofluorene in both tester strains, whereas extracts from unfermented milk had no effect. Extracts prepared from milk fermented by L. bulgaricus plus S. thermophilus showed significantly (P less than .05) more antimutagenic activity than extracts prepared from milk fermented by S. thermophilus alone. Solvent (acetone vs. ethyl acetate) effect was not significant with 4-nitroquinoline-N-oxide as mutagen. However, in the case of 2-aminofluorene, acetone extracts showed significantly (P less than .05) higher antimutagenic activity. The results of this and related studies strongly indicate that antimutagenic compounds are produced in milk during fermentation by S. thermophilus and L. bulgaricus.