Produzione di polisaccaridi e composti antiossidanti da parte di ceppi di lievito non-Saccharomyces dopo crescita e lisi indotta

Non-Saccharomyces yeasts (NSY) represent a consistent part of natural microflora of grape must. Recently, there was an increasing interest in their use for winemaking, since they show a good ability to release higher amounts of polysaccharides compared to Saccharomyces spp. during alcoholic fermentation; furthermore, a non-negligible contribution in increasing glutathione content in sequential or mixed fermentations was also reported, as well as an improvement of wine quality in terms of color stability and aroma profile. However, few studies have been carried out till now about their contribution during wine aging on lees. For this reason, twenty yeast strains were isolated from must and pomace of red grapes cv. Merlot, supplied by a local producer (Friuli Venezia Giulia, North-East Italy). The identification was carried out by colony morphology (on differential WL Nutrient Agar plate), cell morphology (100x optical microscopy) and by genetic characterization. The ability of the isolated strains to produce compounds of enological interest was assessed after growth in standardized conditions (48h at 30°C under anaerobic conditions) and after enzyme-assisted lysis, performed by addition of β-glucanase (5% w/v) and incubation at 45°C for 24h. Biomass production (by weighting), cell viability (by serial dilution and counting of viable cells after 48h at 30°C), the release of polysaccharides (by ethanol precipitation and SE-HPLC analysis), amino acids, thiol compounds (determined spectrophotometrically) and total glutathione (by enzymatic assay) were analyzed. Cell viability (about 107 CFU/mL) was quite similar among the strains tested, whereas for all the other parameters evaluated, differences were observed not only among the genera, but also intra-genus. Basically, strains that produced higher content of soluble compounds, in particular polysaccharides, thiol compounds and total glutathione during the growth phase, also showed the highest release of such molecules after lysis treatment. Among these, interesting results were generally obtained for the strains belonging to Hanseniaspora spp., with the highest content of polysaccharides and antioxidant compounds released both after growth and lysis, together with a biomass production comparable to that obtained by commercial Saccharomyces and Torulaspora strains used as reference. These results might suggest that a correct management of wild microflora might impact on wine composition and quality not only during fermentation but also during aging on lees. The most promising NSY might be also interesting to produce fermentation starters or inactive dry yeast preparations, e.g., autolysates, naturally rich of compounds of enological interest.