Investigating the glutathione accumulation by non-conventional wine yeasts in optimized growth conditions and multi-starter fermentations

Glutathione (GSH) is the most abundant non-protein thiol in yeasts and plays an important role as antioxidant in wine. Application of selected GSH-accumulating strains can improve wine sensorial quality and stability, but most selection programs have been conducted on Saccharomyces cerevisiae. Therefore, the aim of the study was to evaluate the ability of different non-Saccharomyces yeasts, i.e. Lachancea thermotolerans, Metschnikowia spp. and Starmerella bacillaris, to produce glutathione. This feature was evaluated in an optimized medium under aerobiosis (MGSH) and in microfermentations using synthetic grape juice (SGJ) and pasteurized grape juice (PGJ), in single or sequential inoculations with S. cerevisiae. The non-Saccharomyces yeasts showed a good capacity to produce GSH, particularly Metschnikowia spp., which achieved significantly greater concentrations. As expected, the strains presented higher growth and glutathione accumulation in MGSH than in SGJ and PGJ. In the microvinification trials, GSH production was higher in PGJ than SGJ, while cell growth was similar, indicating the influence of grape juice composition on GSH metabolism. Taken together, our results demonstrated that selected non-conventional yeast strains, with proven interesting oenological traits, have a good potential to produce GSH, and thus are more suitable and worthwhile for application as active or inactivated dry yeasts preparations.