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 50mM sodium nitrite (pH 2) at 37 degrees 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-beta-carboline-3-carboxylic acid, 1-methyl-1,2,3,4-tetrahydro-beta-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.