Wine strain improvement strategies to enhance red wine safety based on parietal adsorption activity. 3. Selection of Spanish, Portuguese and Sicilian wine yeasts

Aim of this study was to perform a specific selection of yeasts for red winemaking. Using a phenotypic-based methodology 99 strains of Saccharomyces cerevisiae able to easily sporify, low H2S-producing, low acetic acid-producing, not foam producing and exhibiting high fermentation power during red winemaking have been selected from a major yeast collection. In a second step, a Petri plate evaluation of wine colour adsorption phenotype of yeasts and the result confirmation by microvinification trials were carried out. Strains were split based on their ability to adsorb phenolic grape pigments to identify a maximum of ten strains, the lowest adsorbing ones. The 99 strains of S. cerevisiae were isolated from Spanish, Portuguese and Sicilian musts and wines and are included in the Department of “Scienze Agrarie e degli Alimenti” collection. The yeasts were studied in Petri plates for the following biochemical characteristics: spore production on acetate agar at 25°C for 10d, H2S production on BiGGY agar at 25°C for 48h, acetic acid production on calcium carbonate agar at 25°C for 7d, adsorption of grape pigments on grape skin agar at 28°C for 10d (Caridi et al., 2002; 2007). The microvinification trials were performed using Calabrian black grapes from the cultivar Gaglioppo; the grapes were destemmed, crushed and soaked at 0°C for 3 days, performing a punch down twice per day. The must obtained after pressing was divided in aliquots of 20 ml and fermented at 20°C with the 99 pre-selected yeasts inoculated at 5% in triplicate. Analyses were performed on diluted wine and values were reported considering the dilution. Significant differences for each parameter were observed. Biomass colour varied from 51 to 129 (red component), from 27 to 88 (green component), and from 31 to 82 (blue component). Wine parameters vary from 0.782 to 3.480 (420 nm), from 0.497 to 2.105 (520 nm), from 0.148 to 0.950 (620 nm), from 1.452 to 6.535 (intensity), from 1.304 to 2.040 (tint), from 6.150 to 25.483 (Folin-Ciocalteu index). Based on these results, parietal adsorption activity is notably different among yeasts and justifies a programme of genetic improvement. References Caridi A. et al., (2002), J Gen Appl Microbiol, 48, 261. Caridi A. et al., (2007), J Appl Microbiol, 103, 735.