Isolation and screening of superior yeasts from Yilite strong-flavor Daqu and optimization of Fuqu-making process

In this study, using Yilite strong-flavor (Nongxiangxing) Daqu as the screening material, the superior yeast was isolated and screened by traditional culture separation method and ethanol production performance analysis. The strains were identified by morphological observation and molecular biology technology. The pure yeast Fuqu was made by the screened strains, and using the ethanol content of fermentation liquor as the response value, the Fuqu-making process was optimized by single factor and response surface tests. The results showed that a yeast strain LX-2 with good ethanol production was screened and identified as Saccharomycopsis fibuligera. The optimal conditions for making pure Fuqu with strain LX-2 were as follows:inoculum 11%, fermentation temperature 29 ℃and time 54 h, and water addition 55%. Under these optimal conditions, the ethanol yield of yeast LX-2 was 6.17%, the total ester and total acid contents were 0.223 g/L and 0.078 g/L, respectively. The activities of saccharifying enzyme and liquefaction enzyme were 370.00 U/g and 530.40 U/g, respectively, indicating that the yeast Fuqu had the ability to produce ethanol, but also had certain activities of saccharifying enzyme and liquefaction enzyme. This study had certain reference significance for the isolation and screening of superior yeast in Yilite strong-flavor Daqu and the preparation of Fuqu.