Study of carbohydrate influence on protein–tannin aggregation by nephelometry

The formation of polyphenol/BSA aggregates was measured by nephelometry; the amount of insoluble complexes increased with BSA concentration up to a maximum turbidity value but, in the presence of excess protein, a solubilization of the complexes was observed. The stoicheiometry of the complex at the point of maximum light scattering was calculated, yielding a molar ratio, tannin/BSA, of 7:1. Increase in ionic strength by NaCl addition decreased the amount of protein/tannin aggregates, suggesting that hydrophilic forces are the main driving forces in the complexation between BSA and condensed tannins. The influence of the following carbohydrate concentration on the interactions of BSA with procyanidin compounds was assayed using nephelometry: dextran, glucose, arabinogalactan, β-cyclodextrin, pectin, gum arabic, polygalacturonic acid and xanthan. Overall, carbohydrate concentration induced a solubilization of the protein/tannin complexes, with neutral and ionic polysaccharides displaying different behaviours in this process. Pectin, xanthan, polygalacturonic acid and gum arabic were much more effective in solubilizing the protein/tannin aggregates than glucose, dextran, β-cyclodextrin or arabinogalactan.