| dc.description.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. | |
