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 dur ing alcoholic fermentation in synthetic medium and red wine was Studied. Po lysaccharides after isolation from media by ethanol precipitation were quan tified by a colourimetric method as well as by HPLC assay in wines. Yeast s trains differed in their capacity to release polysaccharides into the mediu m and a maximum concentration of 100mg/L was observed. For all strains, rel ease varied according to metabolic phase, with greater release occurring wh en the yeast mortality rate was high. Mannose was the main component (90%) of these polysaccharides, with the exception of yeast strain BM45 which con tained 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.