Aggregation of grape seed tannins in model wine - effect of wine polysaccharides

The ability of grape seed tannins to aggregate into colloidal-size range particles in a model wine was evidenced by DLS. In the present experimental conditions, they formed aggregates with mean apparent diameters increasing with time. These mean apparent diameters were shown to increase with the concentration (from 0.5 to 2 g/l) and with the mean degree of polymerisation (mDP from 1.7 to 11.3) of the studied fractions. The incidence of wine polysaccharides on tannin aggregation was investigated with six polysaccharidic fractions purified from a red wine and representing the major wine polysaccharides: arabinogalactan-proteins (AGP0 and AGP4), mannoproteins (MPO and MPI) and rhamnogalacturonan II monomer and dimer (RGII-m and RGII-d). Polysaccharides did not prevent initial tannin aggregation, but they influenced particle size evolution. Neutral AGP0 and RGII monomer had no impact on tannin aggregation, whereas it was strongly inhibited by MI's under wine concentration (50 mg/l) and acidic AGP4 at the same concentration. With RGII dimer at its concentration in wine, mean apparent diameter of particles was strongly enhanced, suggesting co-aggregation between this polysaccharide and tannin particles. (C) 2001 Elsevier Science Ltd. All rights reserved.