Decreased ethyl carbamate generation during Chinese rice wine fermentation by disruption of CAR1 in an industrial yeast strain.

Saccharomyces cerevisiae metabolizes arginine to ornithine and urea during wine fermentations. In the fermentation of Chinese rice wine, yeast strains of S. cerevisiae do not fully metabolize urea, which will be secreted into the spirits and spontaneously reacts with ethanol to form ethyl carbamate, a potential carcinogenic agent for humans. To block the pathway of urea production, we genetically engineered two haploid strains to reduce the arginase (encoded by CAR1) activity, which were isolated from a diploid industrial Chinese rice wine strain. Finally the engineered haploids with opposite mating type were mated back to diploid strains, obtaining a heterozygous deletion strain (CAR1/car1) and a homozygous defect strain (car1/car1). These strains were compared to the parental industrial yeast strain in Chinese rice wine fermentations and spirit production. The strain with the homozygous CAR1 deletion showed significant reductions of urea and EC in the final spirits in comparison to the parental strain, with the concentration reductions by 86.9% and 50.5% respectively. In addition, EC accumulation was in a much lower tempo during rice wine storage. Moreover, the growth behavior and fermentation characteristics of the engineered diploid strain were similar to the parental strain.