Purification and structural characterization of a type II Arabinogalactan-protein from Champagne wine
Résumé
Some arabinogalactan-proteins (AGPs) isolated from red wine have interesting physicochemical and sensory properties. An AGP was isolated from a Champagne wine by anion-exchange, affinity, and size exclusion chromatography. Glycosyl residue analysis showed that it included arabinose (12.8%), galactose (68.5%), glucuronic acid (5.9%), and trace rhamnose (0.7%). Champagne AGP reacted with Yariv reagent in gel diffusion tests. The protein part of the AGP primarily contained hydroxyproline (22% of total amino acids), serine (17.6%), alanine (10.8%), glutamic acid (10.3%), and threonine (8.6%). Methylation analysis revealed that the carbohydrate moiety of the glycoprotein had a highly branched structure. The core consisted of 3-linked beta-D-galactopyranose units carrying side chains of 6-linked beta-D-galactopyranose, partly substituted in position 3 and 4 by L-arabinofuranosyl residues. Galactose and arabinose as well as rhamnose and glucuronic acid occurred in terminal positions. Size exclusion chromatography with multiangle laser light scattering of the Champagne AGP revealed apparent average molecular weight mass of 1.1 x 10(5) g/mol, characterized by a narrow polydispersity index (M-w/M-n 1.09) and a very low intrinsic viscosity ([eta] = 0.1 dL/g).