Wine strain improvement strategies to enhance red wine safety based on parietal adsorption activity. 1. Two-step selection of Calabrian and Sicilian wine yeasts

Aim of this study was to perform a two-step selection of 283 wine yeasts. In the first step, a phenotypic-based methodology was employed to identify a maximum of 100 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. In the 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 283 strains of S. cerevisiae have been isolated from Calabrian and Sicilian musts and wines in a period of twenty years and are included in the Department STAFA collection (over than 700 strains). 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 98 wine 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 55 to 153 (red component), from 27 to 124 (green component), and from 32 to 111 (blue component). Wine parameters vary from 0.658 to 3.878 (420 nm), from 0.407 to 2.262 (520 nm), from 0.095 to 1.005 (620 nm), from 1.168 to 7.145 (intensity), from 1.478 to 1.800 (tint), from 7.883 to 33.967 (Folin-Ciocalteu index). Based on these results, parietal adsorption activity is notably different among yeasts and justifies a programme of genetic improvement of the strains. References Caridi A. et al., (2002), J Gen Appl Microbiol, 48, 261. Caridi A. et al., (2007), J Appl Microbiol, 103, 735.