CHARACTERIZATION OF 5 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 chrom atography. Together they represent more than 40% of total wine polysac charides, confirming the abundance of AGPs in red wine. The five purif ied fractions had a common arabinogalactan core with characteristics t ypical 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 linka ge 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 Rha p-(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 presenc e of AG-rhamnogalacturonan fragments.