Protection of wine from protein haze using Schizosaccharomyces japonicus glycoproteins

The release of high concentrations of glycoproteins in the fermentation medium makes the yeast Schizosaccharomyces japonicus particularly interesting, not only for its possible direct use in mixed fermentations with S. cerevisiae but also for the industrial production of glycoproteins which could be purified and subsequently used as additives in winemaking. The possibility of recovering these macromolecules directly from the media allows retention of the native structure of the glucan and, at the same time, avoids the necessity for cell wall enzymatic treatment. There are many advantages associated with the use of such macromolecules during winemaking such as improving mouth-feel and fullness, decreasing astringency, increasing sweetness and roundness and reducing protein and tartrate instability. With the present work, we quantified by HPLC the glycoproteins released by Sch. japonicus after thirteen days of alcoholic fermentation of a synthetic polysaccharide-free grape juice. Glycoproteins were then characterized by gel electrophoresis and their carbohydrate composition analyzed by HPLC. The glycoproteins released in the media were then purified by ultrafiltration (10kDa cut-off) and two different fractions (<50kDa and > 50 kDa) were obtained. After freeze drying, various concentrations of each fraction were added to a protein-unstable wine. After 13 days of fermentation, the concentration of glycoproteins was about 1,2 g/L. The glycoproteins characterization highlighted the presence of elevated percentages of galactose and mannose and low percentages of glucose and proteins, thus confirming what has been observed in previous studies. Although to different extents, both fractions of glycoproteins positively contributed to the protein stability of the wines. Indeed, significant reduction of the protein haze induced by heat was observed after the addition of glycoproteins to the unstable wine.