Influence Of Phytosterols And Ergosterol On Wine Alcoholic Fermentation For Saccharomyces Cerevisiae Strains

Abstract

Sterols are a fraction of the eukaryotic lipidome that is essential for the maintenance of the cell membrane integrity and their good functionality. During alcoholic fermentation, they ensure yeast growth, metabolism and viability, as well as resistance to osmotic stress and ethanol inhibition. Two sterol sources can support yeasts to adapt to fermentation stress conditions: ergosterol, produced by yeast in aerobic conditions, and phytosterols, plant sterols found in grape musts imported by yeasts in anaerobiosis. Little is known about the physiological impact of the assimilation of phytosterols in comparison to ergosterol and the influence of sterol type on fermentation kinetics parameters. Moreover, studies done until today analyzed a limited number of yeasts strains. For this reason, the aim of this work is to compare the fermentation performances of 27 Saccharomyces cerevisiae wine strains with phytosterols and ergosterol on two conditions: sterol limitation and osmotic stress (the most common stress during fermentation due to high concentrations of sugars).

Experiments were performed in 300 mL fermenters without oxygen and monitored in order to obtain kinetics parameters. Cell count and cell viability were measured around 80% of fermentation progress. Central carbon metabolism (CCM) metabolites were quantified at the end of fermentation.

Principal Component Analysis revealed the huge phenotype diversity of strains in this study. Analysis of variance indicated that both the strain and the type of sterol explained the differences on yeast fermentation performances. Strains with a high viability at the end of the fermentation finished fermenting earlier. Finally, ergosterol allowed a better completion of fermentation in both stress conditions tested.

These results highlighted the role of sterols in wine alcoholic fermentation to ensure yeast growth and avoid sluggish or stuck fermentations. Interestingly, sterol type affected yeast viability, biomass, kinetics parameters and biosynthesis of CCM metabolites.