Résumé
For the past decades, yeast assimilable nitrogen has been the focus of wine yeast nutrition as a mean to achieve faster and safer fermentations. Although important, recent studies have shown that other micronutrients play an equal crucial role in fermentation success, particularly by their balanced presence in the grape must. It is the case of sterols. 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 process. 27 commercial wine Saccharomyces cerevisiae yeast strains were screened for their sterol requirements. A high strain dependency was observed showing that in the face of climate change nutritional imbalances or the clarification practice, different strains will be better suited to face lipid limitations. Sterol origin (phytosterols vs ergosterol) also showed to have a distinct impact on key fermentation parameters like yeast population, viability and fermentation rate, often connected with nitrogen assimilation. An impact on final wine aromas was also observed. Finally, transcriptomic analyses provide new insights into the mechanisms underlying the differences observed under sterol limitation with ergosterol or phytosterols. By better protecting and stabilizing yeast plasmatic membranes, sterols can optimize overall yeast metabolism, leading to an increase in fermentation process and aroma production.