Yeast-derived volatile compounds in wines: influence of the yeast strain and the temperature of fermentatión.

Abstract

A major challenge for the national wine industry is to maintain good and reproducible quality in wines. Aroma is a key feature in wine quality and results from the presence of numerous volatile compounds in concentrations that are detectable by our olfactory receptors. Many volatile compounds are produced during the fermentation step, in which the wine yeast Saccharomyces cerevisiae releases, transforms and synthesises a variety of metabolites. In this thesis, the impact of two central variables of the winemaking process, the yeast strain and the temperature of fermentation, on the production of volatile compounds was assessed at the physiological, metabolic and transcriptomic levels of the yeast. Two wine yeasts, S. cerevisiae EC 1118 and VIN 13, and two fermentation temperatures, 15 oc and 28 °C, typical of white and red wine fermentations respectively, were used to carry out batch fermentations with chemicallydefined must. Using Principal Component Analysis, the diverse fermentation conditions were differentiated based on the composition of their final volatile compounds. Furthermore, a significant effect of the strain and temperature on the final concentration of most volatile compounds was demonstrated using Analysis of Variance. Additionally, differential expression of genes involved in aroma biosynthetic pathways was observed in fermentations at 15 oc and 28 °c. Global transcriptome analysis of S. cerevisiae strain VIN 13 showed that genes involved in carbon, nitrogen and fatty acid metabolism, and stress response were expressed in chemostat conditions equivalent to the mid-exponential phase of white wine fermentations. Interestingly, uncharacterised genomic sequences and not previously reported sequence-tags were expressed, which could account for the favourable adaptation capacities of wine strains to winemaking. This work contributes to the understanding of the metabolism of yeast-derived volatile compounds during wine fermentation. Progress on this research area is fundamental to the winemaking industry to attain high quality wines and better performing yeast strains.