Augmenting Effect of a Nonmutagenic Fraction in Soy Sauce on Mutagenicity of 3‐Diazotyramine Produced in the Nitrite‐treated Sauce

When 25 kinds of Japanese soy sauce at a concentration of 5% were incubated with 50m M sodium nitrite (pH 2) at 37° for 1 hr, the reaction mixtures induced 34‐834 (average 368 × 228) revertants per microliter of soy sauce equivalent in Salmonella typhimurium strain TA100 in the absence of S9 mix. The mutagen(s) formed was very unstable under natural daylight and a fluorescent lamp but quite stable under a yellow lamp as well as in the dark. In addition to the known precursors, i.e., tyramine and 1‐methyl‐1,2,3,4‐tetrahydro‐β‐carboline‐3‐carboxylic acid, 1‐methyl‐1,2,3,4‐tetrahydro‐β‐carboline, which caused weak mutagenesis, was found in the soy sauce. However, the sum of the activities of the three mutagen‐precursors after nitrite treatment accounted for only a part of the mutagenicity of nitrite‐treated soy sauce. There was in the soy sauce a factor which increased ninefold the mutagenicity of nitrite‐treated tyramine, 3‐diazotyramine. Therefore, tyramine was considered the principal precursor of the mutagen produced in the nitrite‐treated soy sauce. These three precursors together with the mutagenicity augmentation accounted for all the mutagenicity of nitrite‐treated sauce. The mutagenicity‐augmenting factor in the soy sauce was nonmutagenic before and after nitrite treatment and was stable to heat and light irradiation.