Release of polysaccharides by yeasts and the influence of released polysaccharides on colour stability and wine astringency

Release of polysaccharides by three strains of Saccharomyces cerevisiae during alcoholic fermentation in synthetic medium and red wine was Studied. Polysaccharides after isolation from media by ethanol precipitation were quantified by a colourimetric method as well as by HPLC assay in wines. Yeast strains differed in their capacity to release polysaccharides into the medium and a maximum concentration of 100mg/L was observed. For all strains, release varied according to metabolic phase, with greater release occurring when the yeast mortality rate was high. Mannose was the main component (90%) of these polysaccharides, with the exception of yeast strain BM45 which contained approximatively 50% glucose and 50% mannose. This composition may be related to cell wall composition. The results suggest that polysaccharides can combine with anthocyanins and tannins in wine. This combination seems to increase colour stability and decrease astringency.