EXPLORING THE INFLUENCE OF S. CEREVISIAE MANNOPROTEINS ON WINE ASTRINGENCY AND THE IMPACT OF THEIR POLYSACCHARIDE STRUCTURE

Abstract

Mannoproteins (MPs) are proteoglycans from the outmost layer of yeast cell walls released into wine during alcoholic fermentation and ageing on lees processes. The use of commercial preparations of mannoproteins as additives to improve wine stability with regards to the crystallization of tartaric salts and to prevent protein haze in the case of white and rosé wines is authorized by the OIV.

Regarding red wines and polyphenols, mannoproteins are described as able to improve their colloidal stability and modulate the astringent effect of condensed tannins. The latter interact with salivary proteins forming insoluble aggregates that cause a loss of lubrication in the mouth and promote a drying and puckering sensation. However, neither the interaction mechanisms involved in mannoproteins capacity to impact astringency nor the structure-function relationships related to this property are fully understood.

The aim of this study was to evaluate the impact of high molecular weight mannoproteins on tannin-protein interactions. To this end, experiments were performed in a model wine using tannins purified from a red Syrah wine and BSA. Tannin-BSA aggregation kinetics were followed for 1 hour through Dynamic Light Scattering measurements in the absence and presence of mannoproteins. To progress in the identification of structure-function relationships and on the part played by the polysaccharide part, mannoproteins fractions from four yeast strains were extracted and purified. Yeast Strains were selected according to their origin and specific mannoprotein polysaccharide structure: a commercial enological strain (MP-LMD47), the wild-type BY4742 strain (MP-WT), and two of its mutants ΔMnn4 (MP-Mnn4, no mannosyl-phosphorylation) and ΔMnn2 (MP-Mnn2, linear N-glycosylation backbone). A thorough characterization of mannoprotein fractions confirmed the structural differences between mannoproteins from each yeast strain.

MPs were capable of delaying tannin-BSA aggregation kinetics by preventing the formation of micron-sized particles within the hour of measurement but did not avoid the long-term precipitation of tannin-BSA aggregates. Experiments indicated that mannoproteins interfere with tannin-BSA enlarged aggregation through the formation of a ternary MP-Tannin-BSA system. To be able to prevent tannin-BSA particle growth, the density/compactness of the polysaccharide moiety of MPs was a key factor.