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Human exploitation of yeast fermentation dates back to the Neolithic. S. cerevisiae has been the most important yeast used for numerous fermentations of biotechnological interest, including grape fermentation for wine production. Despite its abundant use, the molecular mechanisms controlling alcoholic fermentation are rather unclear and the choice of S. cerevisiae as an inoculum is often the consequence of a mere habit, rather than the result of rational analyses. In this work we focused on the role of different yeasts in the winemaking process. I was interested in understanding how the specific strain used for inoculum could influence the wine aroma formation. Furthermore, I wished to investigate the yeast genetics and ecology by characterizing their population and strain diversity in one of the wine regions of Slovenia. To evaluate the effect of the yeast species on the fermentation outcome, we performed successive fermentations with five different species in combination with the industrial strain S. cerevisiae Lalvin T73. The experiment showed that at least two more yeast species, Kazachstania gamospora and Zygosaccharomyces kombuchaensis have good potential to be applied in the winemaking. , The main conclusions of this study are the possibility of: i) expanding the palette of alternative starters to widen the aromatic components ii) co–fermenting using two different yeast species. Mixed yeast culture fermentations are present in the natural context, but this practice has been neglected in biotechnological processes. Positive results of wine fermentations with non – conventional yeast urged us to explore the diversity of Slovenian wine region natural isolates. The resulting yeast collection counts more than 1200 strains for which phenotype and genotype have been defined. Numerous isolates, including non – Saccharomyces species, showed promising oenological and biotechnological traits because of their capacity of rapid utilization of various carbon sources, growth at low pH and at presence of copper sulfite and potassium metabisulfite. Sampling also revealed sharp discrimination between the ecological niches of S. cerevisiae and S. paradoxus, which is a striking feature of European vineyards. While S. cerevisiae habitats are strongly associated with human activity, S. paradoxus was mainly isolated from the forest sources. Profound analysis of the collected data could give some explanations to the driving forces of S. cerevisiae domestication and S. paradoxus geographic isolation population structure. |
