Selection of Non-Saccharomyces Yeasts and Effect of Co-fermentation with Them and Rhizopus on the Volatile Flavor Components of Fermented Glutinous Rice Wine

To solve the current problems of fermented glutinous rice wine produced with traditional Jiuqu as a fermentation starter such as unstable quality, weak aroma and high alcohol content, this study selected non-Saccharomyces yeast strains with ester-producing and aroma-enhancing characteristics from traditional Jiuqu by analyzing the structure of its fungal community, and explored the effects of co-fermentation with each selected strain and Rhizopus arrhizus on the volatile flavor components of fermented glutinous rice wine. The results showed that Ascomycota and Mucoromycota were the dominant fungal phyla in Jiuqu and Rhizopus and Saccharomycopsis were the major fungal genera. Four non-Saccharomyces yeast strains, JLY1–JLY4, were obtained, and JLY1 and JLY2 were identified by sequencing as Saccharomycopsis fibuligera, while JLY3 and JLY4 as Torulaspora delbrueckii and Wickerhamomyces anomalus, respectively. Co-fermentation with JLY2 and Rhizopus arrhizus increased the number of volatile components from 46 to 62 compared with the control group, increasing the numbers of esters and alcohols and significantly increasing the relative contents of major flavor compounds such as isoamyl alcohol, phenylethanol, and phenylethyl acetate. Partial least squares-discriminant analysis (PLS-DA) was performed on 40 volatile flavor components shared by fermented glutinous rice wines, and 20 differential flavor substances were selected using the cut-off of variable importance for the projection (VIP) value ≥ 1, including 5 alcohols, 10 esters, 3 acids, 1 aldehyde or ketone, and 1 alkane. Differential substance analysis and sensory evaluation indicated that JLY1 and JLY2 were better than the other strains in terms of ester production and aroma enhancement, and synergistic fermentation significantly enhanced the contents of volatile flavor substances in fermented glutinous rice wine and consequently improved its quality.