Effects of fortified starter culture containing Saccharomyces cerevisiae and Lactobacillus fermentum on microbial community structure and ethyl carbamate

Ethyl carbamate (EC) is a potential carcinogen that is mainly produced by the spontaneous reaction between urea and ethanol during Huangjiu (Chinese rice wine) brewing. In the traditional fermentation process, the starter plays an important role. However, the complex and diverse microorganisms in the starter make it a great challenge to control EC effectively. In this study, two isolated functional strains Saccharomyces cerevisiae G2 (with the capacity of urea utilization) and Lactobacillus fermentum d6 (with the capacity of acid EC-degrading enzymes producing) were used to fortify the starter culture, which regulated the metabolic activity of the microbial community and contributed to the control of EC content in Huangjiu. The high-throughput sequencing analysis showed that fungi (Saccharomyces, Aspergillus, Issatchenkia, and Rhiziopus) and bacteria (Lactobacillus, Streptophyta, and Aeromonas) were dominant microorganisms. Through the analysis of the correlation between the 34 main volatile compounds and the dominant microorganisms, it was found that lactic acid bacteria (Lactobacillus, Leuconostoc, and Lactococcus), Saccharomyces, and Torulaspora were positively correlated with volatile compounds (alcohols and esters). More importantly, fortified starter culture with these strains reduced the urea and EC content in Huangjiu significantly. The obtained results suggested that the EC content in Huangjiu could be regulated by changing the starter culture.