Molecular and physiological characterization of Saccharomyces cerevisiae strains from fermented must and grape marcs

Saccharomyces cerevisiae species dominate the middle-final phases of fermentation in must, but it is also responsible for ethanol production during storage of grape marcs, the main by-product of wine industry, which can be processed for the production of distillates. Grape marc is quite different than must in terms of composition as it consists of solid parts remaining after juice separation, but also for chemical properties. Due to the higher pH, the presence of sugars and other nutritional compounds, it seems to be a more favourable environment than must for the development of yeasts. The aim of this work was to compare the biodiversity of S.cerevisiae strains during spontaneous fermentation of must and grape marcs obtained from the same grape processing, and to study the physiological properties that can be responsible for strain adaptation to the two enological environments. Two grape varieties from north-east of Italy were considered, Glera and Tocai friulano. Mitochondrial DNA analysis performed on Saccharomyces isolated after 6 days and at the end of fermentation, allowed the strain characterization of 100 isolates from must and grape marc, respectively. Some strains were found to be in common to both environments, but others prevailed only on marc. The causes were investigated analyzing some physiological characteristics that can confer an advantage to strains developing in grape marcs as growth at different pH values and yeast enzymatic activities for plant component degradation. Since skins can be richer that must of fungicide residues, resistance of yeasts to increasing copper concentration was also evaluated.