Compositional and structural characterization of mannoprotein extracts obtained from non-Saccharomyces wine yeasts

Abstract

Mannoproteins (MPs) constitute one of the most abundant classes of wine polysaccharides. They are proteoglycans located in the yeast cell wall that are composed by a major polysaccharide moiety (formed mainly by mannose) linked to a minor protein part. MPs are naturally released by yeast into the wine during alcoholic fermentation and during wine ageing on lees. Moreover, in winemaking, MP extracts can be added to the wine to improve some technological and sensory properties, such as protein and tartaric stability, astringency, color stability and aroma persistence, among others. However, some inconsistencies regarding the use of MPs in winemaking can be found in the literature, which can be explained by the high structural diversity of MPs conditioning their techno-functional properties in wine [1]. Moreover, most of the studies up to date have focused on MPs from Saccharomyces cerevisiae, while few information is available about MPs originating from non-Saccharomyces species. In this context, a more detailed characterization of MP structural diversity is needed in order to clarify structure-activity relationships, which would allow an effective use of these biopolymers in the wineries. Therefore, the objective of this work was to perform an in-depth characterization of MP extracts obtained from S. cerevisiae and from non-Saccharomycesyeasts. Ten MP extracts were obtained from five commercial enological yeasts (S. cerevisiae, Lachancea thermotolerans, Metschnikowia pulcherrima, Pichia kluyveri and Torulaspora delbrueckii) through induced autolysis and enzymatic hydrolysis with a β-1,3-glucanase. The monosaccharide composition, determined by GC-FID, varied among the extracts, indicating different degrees of MPs purity. Moreover, the glycosyl-linkage composition, determined by GC-MS, also showed substantial variation, suggesting differences in the structure of the polysaccharide moiety of MPs belonging to different wine yeast species. Characterization of the net charge of MPs showed that almost all extracts obtained would display a net negative charge at wine pH. Finally, HPSEC-MALLS-QELS analysis allowed the identification, within each MP extract, of several MP populations likely exhibiting different macromolecular conformations, which highlighted the structural complexity of the MP extracts. Overall, these results offer valuable information regarding the impact of the extraction method and the yeast species on MP extract characteristics.

References

[1] Gao, B.; Rao, C..; Lei, X.; Li, S.; Huang, X.; Liu, Y.; Ye, D. (2025). Comprehensive insights into yeast mannoproteins: structural heterogeneity, winemaking, food processing, and medicine food homology. Food Res. Int., 202, 115719.