[Metabolism of ethyl carbamate precursors in soy sauce by Zygosaccharomyces rouxii ZQ02Metabolism of ethyl carbamate precursors in soy sauce by Zygosaccharomyces rouxii ZQ02].

ABSTRACT

Objective: To study nitrogen metabolism of Zygosaccharomyces rouxii and its relationship with the formation of soy sauce ethyl carbamate precursors. Methods: Z. rouxii ZQ02 was cultivated with single source of nitrogen, preferred nitrogen sources or under salt stress, to investigate its ability of using arginine, citrulline and urea. Results: Alanine, glycine and asparaginate were confirmed to be the preferred nitrogen sources of Z. rouxii ZQ02. Addition of preferred nitrogen sources did not inhibit the use of urea and citrulline, on the contrary, the consumption of urea and citrulline by Z. rouxii ZQ02 was stimulated with the addition of alanine and glycine. Z. rouxii ZQ02 did not accumulate any citrulline and urea from degradation of arginine. Urea and citrulline were used by Z. rouxii ZQ02 in the medium with single source of nitrogen. However, use of citrulline and urea by Z. rouxii ZQ02 was strongly inhibited under saline stress, resulting in the incomplete use of ethyl carbamate precursors. Conclusion: Use of citrulline and urea by Z. rouxii ZQ02 was strongly inhibited under high salt stress, resulting in the accumulation of ethyl carbamate precursors produced by other microorganisms during soy sauce fermentation.