Impact of must oxidation on β-lyase coding genes of Saccharomyces cerevisiae and the release of polyfunctional thiols in Sauvignon blanc

Abstract

Polyfunctional thiols represent a potent class of aroma compounds that shape the wine aroma due to their low odor detection thresholds (Darriet et al., 1995). The uptake of thiol precursors in yeast cells, their enzymatic cleavage and the release of volatile thiols has been found to be related to the intracellular oxidation-reduction potential (ORP) influencing the expression of β-lyase coding genes involved in thiol metabolism (Gallo et al., 2026). Must oxidation prior to inoculation is thought to increase the ORP and therefore enhancing the expression of β-lyase coding genes. However, must oxidation may also reduce the concentration of thiol precursors in must causing a decrease of volatile thiol yields in wine (Roland et al., 2010). Consequently, it remains unclear if an optimal balance between these opposing effects exists and if it can be controlled through monitoring ORP during must processing and wine fermentation. Clarified Sauvignon blanc grape must was subjected to different pre-fermentation treatments: (1) addition of 60 mg/L SO₂, (2) protection with dry ice and (3) active air addition. The batches were inoculated with Saccharomyces cerevisiae to start fermentation. ORP was monitored during pre-fermentation treatments until the end of fermentation. Total RNA was isolated from yeast cells, collected at 24, 48, 72, and 96 h after inoculation. After generating complementary DNA (cDNA), quantitative real-time PCR (qPCR) was performed in order to analyze the expression of genes STR3 and IRC7 associated with β-lyase activity. ORP was found to be significantly enhanced by must oxidation. Gene expression during the onset of fermentation was positively correlated to the ORP suggesting the ORP as a potent parameter to control aroma formation. The liberation of polyfunctional thiols can be increased in the wine by controlling the ORP during must processing and wine fermentation in the right corridor.

References

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Gallo, A., Larcher, R., Schneider, R., Barbero, A., Tonidandel, L., Pradal, M., Farines, V., Galeote, V., Roman, T., 2026. Impact of oxygen supplementation during fermentation on yeast gene expression and thiol release in wine. Food Microbiology 133, 104881.

Roland, A., Vialaret, J., Razungles, A., Rigou, P., Schneider, R., 2010. Evolution of S -Cysteinylated and S -Glutathionylated Thiol Precursors during Oxidation of Melon B. and Sauvignon blanc Musts. J. Agric. Food Chem. 58, 4406–4413.