Abstract
Urea, as the main precursor of ethyl carbamate (EC), has received extensive attention. Here, we have metabolically engineered an industrial yeast strain – Saccharomyces cerevisiae N85 – to investigate the contribution of the EC precursor citrulline to the concentration of EC in Chinese rice wine. The results showed that the citrulline biosynthetic pathway of the modified strain N85-arg3 was completely suppressed by deletion of ARG3, encoding ornithine carbamoyltransferase. However, there were no significant differences in the levels of citrulline or EC between N85-arg3 and the parental strain N85 during fermentation. In addition, we over-expressed ARG1 (encoding argininosuccinate synthase) and ARG4 (encoding argininosuccinate lyase) to construct the engineered strains N85ARG1,4 and N85ARG1,4-arg3. The citrulline contents in Chinese rice wine fermented with N85ARG1,4 and N85ARG1,4-arg3 were respectively 24.1 and 20.4% less than that of N85. However, the contents of EC were 23.8 and 28.5% more than that of N85. These results suggested that reducing the formation of EC during Chinese rice wine fermentation by genetically engineering citrulline metabolism in S. cerevisiae was not a viable proposition. Copyright © 2018 The Institute of Brewing & Distilling
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