Characterization of five type II arabinogalactan-protein fractions from red wine of increasing uronic acid content.

Five arabinogalactan-protein conjugates (AGP) were separated from red wine by two successive anion-exchange chromatography steps and further purified to apparent homogeneity by affinity and size-exclusion chromatography. Together they represent more than 40% of total wine polysaccharides, confirming the abundance of AGPs in red wine. The five purified fractions had a common arabinogalactan core with characteristics typical of wine type II AGPs, but differed mainly in their uronic acid content, as evidenced by differences in the strength of their binding to the anion-exchanger. Their uronic acid content and glycosidic linkage composition revealed that the three less acidic AGPs contained from 3 to 7% glucuronic acid, half in terminal non-reducing positions and half in terminal Rhap-(1-->4)-Glc pA-(1-->sequences. The two more acidic AGP-containing fractions contained both glucuronic (6.1 and 13.3%, respectively) and galacturonic (1.9 and 2.3%, respectively) acid in association with 2- and 2,4-linked rhamnose, indicating the presence of AG-rhamnogalacturonan fragments.