Reduction of methionine based sulfur-containing carcinogen using halotolerant yeast cells

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J.H.Weisburger, et al.^<1)> isolated a compound, 2-chloro-4-methylthiobutanoic acid (CMBA), capable of inducing gastric cancer from a salted Pacific saury, which is a Japanese processed marine product. CMBA is produced in the presence of methionine, sodium nitrite and sodium chloride, which are used as food additives.In this study, we attempted to reduce the amount of CMBA produced using a halotolerant yeast isolated from a soybean paste. For analyzing the amount of CMBA, we performed a mutagenicity test using Salmonella tryphimurium TA100, histidine auxotrophic mutant of Salmonella or Ames test. The number of reverse mutation colonies decreased depending on the amount of concentrated extract of Zygosaccharomyces rouxii S-2B (halotolerant yeast) was added, and about 30% reduction was observed when 30μl (equivalent to〜1.2×10^7bacteria) of the concentrated extract was added to 50 gg of CMBA.In addition, the inhibitory effects of the yeast cells toward CMBA were determined by culturing. Zygosaccharomyces rouxii S96, a halotolerant yeast, and Saccharomyces cerevisiae RIB6002 (Kyokai No.7) of sake yeast, a non-halotolerant yeast, were used as test strains. Both the strains were cultured with CMBA for 0, 0.5, 3, and 24h. As a result, both strains were found to decrease the amount of CMBA present in the culture with increase in contact time. The reduction rates after 24 h of contact time were 29.7% for Z.rouxii S96 and 14.2% for S.cerevisiae in 24h of contact time. This reduction was probably because CMBA was found to be adsorbed on the positively charged surface of yeast cells. Based on these results, we conclude that CMBA, which is known to cause gastric cancer, can effectively be reduced using halotolerant yeast cells.1) Wei Chen, John H.Weisburger, et. al. : NATURE, 374, 599 (1995)