Impact of oxygen supplementation during fermentation on yeast gene expression and thiol release in wine

Traditionally, oxygen supplementation has been more strongly associated with yeast vitality and sugar consumption kinetics than with aroma metabolism. This study investigated the effects of oxygen exposure during the exponential growth phase of yeast cells on the polyfunctional thiol profile of wine. Using quantitative real-time RT-PCR, the expression of five genes related to amino acid and peptide uptake, as well as two genes associated with β-lyase activity, was analyzed. UPLC/MS-MS was employed to quantify thiol precursors and volatile thiols in must and wine. The results revealed that oxygen upregulated the expression of genes involved in amino acid and peptide uptake, including GAP1, OPT1, OPT2, PTR2, DAL5, and FOT3, some of which are known thiol precursor permeases. Overexpression of those genes in oxygenated trials was correlated with a reduction in thiol precursor residues in wines, particularly GSH-3MH, which was depleted before entry into the stationary phase. Despite increased gene expression, the concentration of GSH-4MMP was not affected and remained constant during the growth phase. Additionally, the expression of the gene responsible for thiol-releasing β-lyases in yeasts, IRC7, was positively correlated with 4MMP concentration in wines when influenced by oxygen treatment during the initial 72 h of alcoholic fermentation. However, oxygen supplementation was associated with STR3 downregulation, which may have contributed to the lower 3 MH release, despite the increased precursor intake.