Screening of Ethyl Carbamate-Degrading Strains from Baijiu Daqu and Optimization of Co-fermentation Conditions

In order to reduce the content of ethyl carbamate (EC), a harmful by-product in the fermentation process of Baijiu, this study isolated bacteria and yeasts with EC-degrading ability and excellent fermentation performance from Daqu, and the co-fermentation conditions for the two microbial species were optimized by response surface methodology and applied to the fermentation of Baijiu. The results showed that 5 strains of yeast and 4 strains of bacteria with high EC-degrading activity were obtained from Baijiu Daqu and screened for ester production ability and protease activity. Bacillus amyloliquefaciens (JX2-10) and Wickerhamomyces anomalus (QX-2) with excellent fermentation performance were obtained. The degradation rates of 200 μg/L EC by JX2-10 and QX-2 were 85% and 35% after 24 h culture, respectively. Using single factor experiments and response surface methodology (RSM) with protease activity and total ester concentration as response variables, the optimal co-fermentation conditions were determined to be 5.6, 30.1 ℃ and 3.9% for initial pH, culture temperature, and ethanol concentration, respectively. Under these conditions, the activity of protease was 41.59 U/mL, and the total ester concentration was 5.85 g/L. EC contents in fermented grains and Baijiu produced using the co-culture decreased by 12.7% and 10.8%, respectively, compared with those of the control group, and the content of volatile flavor substances in Baijiu increased. This study provides a data basis for the degradation of EC during the fermentation of Baijiu.