Schizosaccharomyces japonicus: a polysaccharides overproducing yeast to be used in mixed fermentation

A strain of Schizosaccharomyces japonicus, previously characterized for its capacity to release in a synthetic media a high quantity of polysaccharide (1), has been here evaluated for grape must fermentation in pure and mixed fermentation with a commercial strain of Saccharomyces cerevisiae (EC1118). Different S. cerevisiae/non-Saccharomyces inoculum ratios (trial 1, 1:1;trial 2, 1:100; trial 3, 1:10,000) were investigated. Pure cultures of EC1118 were also used as controls at each of the three levels of inoculum in the mixed cultures. The strain S.japonicus affected the growth of S.cerevisiae only in trial 3 (inoculum ratio 1:10,000). In agreement, the fermentation rates decreased in an inoculum-ratio-dependent fashion. The influence of the inoculation mode on the interactions between the two yeast strains and on the analytical profiles of the final wines was also evaluated. The high release of polysaccharide by the S.japonicus strain was here confirmed. In all the trials the concentrations of total polysaccharides was significantly higher than those of the pure cultures of EC1118. Mixed fermentations showed inoculum-ratio-dependent increases in total polysaccharides. Thus when combined with EC1118, this non-Saccharomyces yeasts might enhance the wine complexity and aroma by increasing the final concentrations of the polysaccharides and improve the wine stability Indeed, polysaccharides have been shown to improve wine ‘mouthfullness’, to positively affects aroma persistence, and to contribute to protein and tartrate stability (2,3,4). The analytical profiles of the wines produced by the mixed cultures indicated that depending on the inoculum ratio, this non-Saccharomyces yeast can be used in mixed fermentation to modulate the final concentrations of malic and acetic acid and some of the most important volatile compounds, such as 2-phenyl ethanol.