Polysaccharide structure of Mannoproteins influences the colloidal outcome of their interactions with grape seed tannins

High-molecular-weight Mannoproteins (MPs) and Low-molecular-Weight Mannoproteins (LMPs) were isolated from purified enzymatic extracts of four different Saccharomyces cerevisiae yeast strains with pure endo -β-glucanases to preserve their native structures. These strains included a reference strain (BY4742), its mutants ΔMnn4 (with no mannosyl-phosphorylation) and ΔMnn2 (with a linear N-glycosylation backbone), and a selected wine yeast strain. MPs and LMPs were then used to study how the structure of their polysaccharide moiety impacts their interactions with Grape Seed Tannins (ST) and colloidal behavior. Beyond molecular weight differences, mannose/protein ratios of LMPs ranged from 0.67 to 1.0, whereas those of MPs ranged from 10.3 to 18.9. Previous studies have confirmed differences in the polysaccharide structure between MPs. Dynamic Light Scattering analyses indicated aggregate formation whose evolution was fraction-dependent. When LMPs were involved, dashing aggregation resulted in sedimentation within a day. ST interactions with MPs alone formed colloids whose size and concentration depended on ST/MP ratio and remained stable beyond 30 days. Isothermal Titration Calorimetry profiles of ST/MP interactions displayed the same typical low-affinity regardless of differences in MPs polysaccharide structure, suggesting, through model-dependent methods, the presence of two kinds of interaction sites with different affinities; both exothermic and thermo-dependent (possibly related to hydrogen bonding).