Charge Properties of Some Grape and Wine Polysaccharide and Polyphenolic Fractions

¹ Institut Supérieur de la Vigne et du Vin, Ecole Nationale Supérieure Agronomique de Montpellier - UFR de Technologie-Oenologie, 2 place Pierre Viala, F-34 060 Montpellier Cedex 1
² Institut Supérieur de la Vigne et du Vin, Institut national de la Recherche Agronomique - Laboratoire des Polymèeres et des Techniques Physico-Chimiques, 2 place Pierre Viala, F-34 060 Montpellier Cedex 1.

Charge densities of the major wine polysaccharides and of grape seed and wine polyphenols have been determined with a method developed by Mütek (Germany), relying on titration with a counter-charged polyelectrolyte associated to streaming potential measurements. Charge densities were determined in a model hydroalcoholic solution at pH 3.5 and in 10 mM KNO₃ solutions, from pH 2 to 9. The polysaccharides tested — yeast mannoproteins, grape arabinogalactan-proteins (AGPs), and rhamnogalacturonan RG-II — carried negative charges in the wine pH range. The net charge density of yeast mannoproteins was shown to be related to their phosphorus content and to be pH-independent in the range tested (2 to 9). Absolute charge densities of AGPs and RG-II were related to the dissociation of the carboxylic functions of their uronic acids and increased dramatically in the pH range 2 to 5. Polyphenolic fractions, including native tannins isolated from grape seeds and polyphenolic fractions recovered from wine, carried no charges or negligible charges at pH 3.5. As a consequence, wine polysaccharides may establish electrostatic and ionic interactions, but such interactions will play little, if any, in the association of polyphenols with other components.

Key words: polysaccharides, mannoproteins, arabinogalactan, rhamnogalacturonan, tannins, procyanidins, charge density, interactions

Submitted on January 9, 1995