Quantification and characterization of cell wall polysaccharides released by non-Saccharomyces yeast strains during alcoholic fermentation.

In order to improve knowledge about the oenological characteristics of non-Saccharomyces yeast strains, and to reconsider their contribution to wine quality, we studied the release of polysaccharides by 13 non-Saccharomyces strains of different species (three wine yeasts, six grape yeasts, and three spoilage yeasts) during alcoholic fermentation in synthetic must. Three Saccharomyces cerevisiae strains were included for comparison. All of the non-Saccharomyces strains released polysaccharides into fermentation medium; the amount released depended on the yeast species, the number of cells formed and their physiological conditions. Normalizing the quantity of macromolecules released to the cell biomass revealed that most non-Saccharomyces strains produced a greater quantity of polysaccharides compared to S. cerevisiae strains after 7 and 14days of fermentation. This capacity was particularly expressed in the studied wine spoilage yeasts (Saccharomycodes ludwigii, Zygosaccharomyces bailii, and Brettanomyces bruxellensis). Chemical characterization of exocellular polysaccharides produced by non-Saccharomyces yeasts revealed them to essentially be mannoproteins with high mannose contents, ranging from 93% for S'codes. ludwigii to 73-74% for Pichia anomala and Starmerella bombicola. Protein contents varied from 9% for P. anomala to 29% for Z. bailii. These compositions were very similar to those of the S. cerevisiae strains, and to the chemical composition of the cell wall mannoproteins of different yeast species. The presence of galactose, in addition to mannose and glucose, in the exocellular polysaccharides released by Schizosaccharomyces pombe, confirmed the parietal nature of the polysaccharides released by non-Saccharomyces yeasts; only this species has a galactomannan located in the outer layer of the cell wall.