Structure of Arabinogalactan and Pectin from the Silybum Marianum

From the leaves of Silybum marianum L. were isolated arabinogalactan with molecular weight 38 kDa and pectic substances. The monosaccharide composition of arabinogalactan was represented by β-galactose and α-arabinose in a ratio of 2.6:1.0 and β-galacturonic acid as a minor component. By chemical methods and GC, GC-MS, 1D and 2D NMR spectroscopy was established that the arabinogalactan consists of d-galactopyranose residues linked by β-1,6-glycosidic bonds as a main chain, and the side chain was represented by α-arabinose, β-galactose and 4-O-methylglucuronic acid. Pectic substance was found in small amounts. According to NMR data it contains also a branched rhamnogalacturonan.