Colloidal dispersions of tannins in water-ethanol solutions.

The molecular interactions of grape-seed tannins dissolved in water-ethanol solutions have been studied through small angle neutron scattering, light scattering, and physical separation techniques. Through selective precipitation in different solvent mixtures, three populations of tannin macromolecules have been identified: T1 (2% of the total tannin), which forms colloidal particles when the ethanol content of the solvent is brought below phiA = 0.6; T2a (33% of the tannin), which phase-separates below phiA = 0.

Polar interactions in flavan-3-ol adsorption on solid surfaces.

The adsorption of flavan-3-ol monomers and grape seed procyanidin fractions of different mean degrees of polymerization was studied on three surfaces by means of adsorption isotherms. Reversibility upon dilution was also investigated. These surfaces were three polymeric microfiltration membranes, presenting close Lifshitz-van der Waals components of their surface tension but differing in their surface polar properties.

Changes in proanthocyanidin chain length in winelike model solutions.

Reactions of seed and skin proanthocyanidins in the presence or absence of (-)-epicatechin were followed in winelike solutions over 53 days at 30 degrees C. Proanthocyanidins were separated from flavanol monomers by sequential elution from a Sep Pak cartridge, and changes in proanthocyanidin composition were monitored by thiolysis analysis of the proanthocyanidin fraction. In solutions containing no free (-)-epicatechin, trace amounts of monomers were released and important losses of proanthocyanidins were measured, but their average composition and mean degree of polymerization (mDP) were hardly modified.