Unveiling the Power of Sterols: Optimizing Wine Fermentation with Strategic Addition
Abstract
Excessive grape must clarification can result in sluggish alcoholic fermentations and sometimes
alcoholic stuck fermentations, because of the lack of sterols for the yeasts growth. To avoid this risk,
addition of sterols (ergosterol or phytosterols) can be performed, resulting in higher
Saccharomyces cerevisiae viability and shorter fermentation duration. However, no dedicated study
was implemented to evaluate the efficiency of different strategies of sterol management (considering
sterol type, added concentration and timing of addition) during wine fermentation. So, first, to evaluate whether the response of wine yeast
strains to sterol nutrition was similar according to the type and the concentration of the sterol present
in the initial must, it was studied the response of a set of 10 S. cerevisiae strains in a synthetic grape
must with low, medium and high concentrations of ergosterol or phytosterols. Then,
the impact of the timing of sterol addition was evaluated on 2 S. cerevisiae strains with opposite
behaviours. This work confirmed previous results concerning the role of ergosterol and phytosterols
but also revealed new findings in this field. At first, it was confirmed that ergosterol played an
important role in improving the maintenance of viable cells towards the end of fermentation,
particularly in sterols-limited situations, while phytosterols demonstrated an ability to reduce acetate
and glycerol production. But, in a second part, our study sheds new light on the beneficial impact of
sterol addition on amino acid assimilation in yeast, leading to an increase in maximum fermentation
rate, biomass production and percentage of viable cells. However, the main novelty of this research
work concerns the timing of ergosterol addition. This addition at the start of fermentation in a
phytosterols-free synthetic must enabled faster fermentations, as well as higher fermentative aroma
synthesis, compared to addition during stationary phase. Even if the
impact of ergosterol additions were relatively similar for both strains tested, notable differences were
found concerning amino acid assimilation and biomass production, suggesting differences in the
regulation of nitrogen metabolism between both strains. These findings provide new insights into our
understanding of sterol role in enological fermentation. It offers a basis for both the development of
innovative strategies for sterol management and the selection of 71 wine yeast strains under sterol
starvation.