Effects of Saccharomycopsis fibuligera on the formation of flavor substances and functional enzymes during turbid rice wine brewing.

Qu is an indispensable saccharifying and fermenting starter for the turbid rice wine (TRW) brewing. Commercial Qu (CQ) employs controlled fermentation of standardized strains to ensure consistent quality but limits aroma complexity, while traditional Qu (TQ) enriches environmental microbiota under open fermentation for richer flavor at the cost of higher process variability and product inconsistency. This study investigated the influence of Saccharomycopsis fibuligera from TQ on TRW quality by comparing fermentation with CQ independently (CW) and CQ supplemented with S. fibuligera (SW). The addition of S. fibuligera significantly reduced the reducing sugar and total sugar in TRW while increasing amino acid nitrogen, total acid, ethanol, antioxidant activity, and volatile compounds. Notably, S. fibuligera had discrepant effects on amino acids, namely, a decrease in bitter amino acids and an increase in sweet amino acids by day 10. The microorganism also enhanced the activities of α-amylase, β-glucanase, β-1,3-glucanase, β-glucosidase, and esterase in fermentation system, and these highly active enzymes could promote the production of unique volatile compounds and give TRW distinctive flavor. Specially, the higher activities of α-amylase, β-glucanase, and esterase might reduce bitterness of SW by decreasing the arginine content. These findings demonstrate that S. fibuligera improves TRW flavor quality through modulation of enzymatic activities in the fermentation system. To our knowledge, this study is the first report on the effects of S. fibuligera on the flavor quality of TRW from the perspective of complex enzymes in fermentation system, providing valuable insights for the application of TQ microorganisms in fermentation processes.