Abstract
Excessive grape must clarification can result in sluggish alcoholic fermentations and sometimesalcoholic 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 studywas implemented to evaluate the efficiency of different strategies of sterol management (consideringsterol type, added concentration and timing of addition) during wine fermentation. So, first, to evaluate whether the response of wine yeaststrains to sterol nutrition was similar according to the type and the concentration of the sterol presentin the initial must, it was studied the response of a set of 10 S. cerevisiae strains in a synthetic grapemust 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 oppositebehaviours. This work confirmed previous results concerning the role of ergosterol and phytosterolsbut also revealed new findings in this field. At first, it was confirmed that ergosterol played animportant 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 acetateand glycerol production. But, in a second part, our study sheds new light on the beneficial impact ofsterol addition on amino acid assimilation in yeast, leading to an increase in maximum fermentationrate, biomass production and percentage of viable cells. However, the main novelty of this researchwork concerns the timing of ergosterol addition. This addition at the start of fermentation in aphytosterols-free synthetic must enabled faster fermentations, as well as higher fermentative aromasynthesis, compared to addition during stationary phase. Even if theimpact of ergosterol additions were relatively similar for both strains tested, notable differences werefound concerning amino acid assimilation and biomass production, suggesting differences in theregulation of nitrogen metabolism between both strains. These findings provide new insights into ourunderstanding of sterol role in enological fermentation. It offers a basis for both the development ofinnovative strategies for sterol management and the selection of 71 wine yeast strains under sterolstarvation.