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

The ability of grape seed tannins to aggregate into colloidal-size range pa rticles in a model wine was evidenced by DLS. In the present experimental c onditions, they formed aggregates with mean apparent diameters increasing w ith time. These mean apparent diameters were shown to increase with the con centration (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 investigate d with six polysaccharidic fractions purified from a red wine and represent ing 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 aggrega tion, but they influenced particle size evolution. Neutral AGP0 and RGII mo nomer had no impact on tannin aggregation, whereas it was strongly inhibite d by MI's under wine concentration (50 mg/l) and acidic AGP4 at the same co ncentration. With RGII dimer at its concentration in wine, mean apparent di ameter of particles was strongly enhanced, suggesting co-aggregation betwee n this polysaccharide and tannin particles. (C) 2001 Elsevier Science Ltd. All rights reserved.