Investigation of novel metabolites generated by Torulaspora delbrueckii to promote the aroma biosynthesis in Saccharomyces cerevisiae during wine fermentation

The co-fermentation of Saccharomyces cerevisiae and non-Saccharomyces has been recognized as an effective strategy for improving the quality of wine aroma. One of the most critical factors for the aroma enhancement is the yeast-produced metabolites, but the underlying mechanisms remain poorly understood. In this study, we used a cell/medium separation strategy to investigate the effects of metabolites generated by Torulaspora delbrueckii on the aroma biosynthesis in S. cerevisiae. The results demonstrated that T. delbrueckii metabolites enhanced the production of ethyl octanoate, ethyl decanoate, isoamyl acetate, and isopentanol within S. cerevisiae. Upregulation of aroma-related genes, including EEB1, SLI1, BAP3, BAT1, PDC1, and PDC5 in S. cerevisiae, was responsible for the aroma enhancement. The untargeted metabolomic analysis determined a total of 869 T. delbrueckii metabolites, in which three novel metabolites were identified to promote the aroma formation in S. cerevisiae. Specifically, 3-amino-4-methylpentanoic acid stimulated the levels of ethyl octanoate (up to 42.55%) and ethyl decanoate (up to 31.92%), while 4-methylaminobutyric acid and citraconic acid increased the production of ethyl hexanoate (up to 59.19%) and isoamyl acetate (up to 32.26%). A comprehensive understanding of the specific yeast metabolites provides a robust foundation for winemakers to purposefully modulate the aromatic characteristics of wines.