Polysaccharide structure of mannoproteins determines their functional interaction with grape seed tannins

Abstract

Colloidal equilibria involving phenolic compounds are essential for the stability and sensory properties of red wines. Mannoproteins (MPs) are known to promote the colloidal stability of tannins, but the specific relationships between their polysaccharide structure and these functional properties remain poorly understood. This study explores how the structure of the polysaccharide moiety and the mannose/protein ratio impact interactions with grape seed tannins (ST) and the resulting colloidal behavior. High-molecular-weight (HMPs) and low-molecular-weight mannoproteins (LMPs) were isolated and purified from enzymatic extracts of four Saccharomyces cerevisiae strains: a reference strain (BY4742), its mutants ΔMnn4 (no mannosyl-phosphorylation) and ΔMnn2 (linear N-glycosylation backbone), and a selected wine yeast strain. Interactions between these fractions and purified grape seed tannins were characterized using Isothermal Titration Calorimetry (ITC), while the resulting colloidal aggregates were monitored over 30 days via Dynamic Light Scattering (DLS) and Nanoparticle Tracking Analysis (NTA). The results indicate that the polysaccharide-to-protein ratio significantly influences solubility in wine-like media; LMPs, with lower mannose content, showed a higher propensity for self-aggregation compared to MPs. ITC profiles revealed that all MPs, regardless of their polysaccharide structure, display similar low-affinity, non-covalent binding sites for tannins. However, DLS analyses showed that the colloidal outcomes were fraction-dependent: while LMPs induced rapid aggregation and sedimentation within 24 hours, MPs formed stable colloids whose size and concentration depended on the ST/MP ratio. Specifically, the branching degree of the polysaccharide moiety played a more critical role in solubility and stability than mannosyl-phosphorylation. These findings highlight that the structural characteristics of yeast mannoproteins are decisive factors in managing tannin-related instabilities in enology.

References

Assuncao Bicca, S.; Poncet-Legrand, C.; Williams, P.; Mekoue Nguela, J.; Doco, T.; Vernhet, A. (2022) Structural characteristics of Saccharomyces cerevisiae mannoproteins: Impact of their polysaccharide part, Carbohydrate Polymers, 277, 118758.