Structural analysis of the polysaccharides from Echinacea angustifolia radix

In this paper we report the characterization by monosaccharide and linkage analyses and by NMR spectroscopy and size exclusion chromatography of the carbohydrate fraction extracted from Echinacea angustifolia radix. In addition, the products of endo-pectin lyase, endo-pectate lyase, endo-polygalacturonase, endo-galactanase, and endo-arabinase digestion were characterized by MALDI-TOF mass spectrometry. The data obtained during this study showed that the carbohydrate fraction extracted from E. angustifolia radix is constituted by two polysaccharides with molecular weight of about 128,000 and 4500 Da. The low molecular weight polysaccharide corresponds to inulin while the high molecular weight component is a high metoxy pectin in which the backbone structure of the smooth region is constituted by α-(1–4)-polygalacturonan partially methyl esterified (60%) and acetylated (9%) and with the hairy regions containing 2-O- and 2,4-O-rhamnopyranose, 5-O- and 3,5-O-arabinofuranose, 3,6-galactopyranose, and terminal rhamnopyranose, arabinofuranose, arabinopyranose, galactopyranose, and galacturonopyranose. Mass spectrometry data of a galactanase treated sample showed evidence of a novel structure in the pectin hairy region, namely a galactose–galacturonic acid alternating sequence.