Résumé
The arabinogalactan-proteins (AGPs) from Acacia senegal gum are used as protective colloid in young red wines to prevent the precipitation of the coloring matter. Usually, Acacia senegal gum is chosen based on its efficiency to stabilize iron hexacyanoferrate salts in hydro-alcoholic solution. In this study, the protective activity of Acacia senegal gum and its macromolecular fractions (HIC–F1, HIC–F2 and HIC–F3), separated according to their hydrophobicity, towards the precipitation of iron hexacyanoferrate salts and polyphenols in hydro-alcoholic solutions are reported. AGPs prevent the colloidal instability of both iron hexacyanoferrate salts and polyphenols in “model” hydro-alcoholic solutions and young red wine with a good correlation between results obtained on both systems. This result strengthens the use of iron hexacyanoferrate salts (hydro-alcoholic – mineral test) for the evaluation of the protective activity of A. senegal gum in young red wine. The precipitation of iron hexacyanoferrate salts is avoided by the electrostatic binding of Ca2+, the driver of the instability, with the negatively charged carried by amino-acids from the protein backbone or both by amino acids and uronic acid monosaccharides localized close to the protein backbone of AGPs. The protective activity closely depends on the protein content of AGPs in both iron hexacyanoferrate salts and polyphenols hydro-alcoholic solutions: the more they are rich in proteins, the more their colloidal stabilizing efficiency is (HIC–F3>HIC–F2>HIC–F1). The differences observed in the protective activity between AGPs from the three HIC fractions are relied not only to their protein content but also to their related rate of glycosylation that modulates the protein accessibility to its environment, then their physicochemical properties as their hydrophobic behavior.