Studies on the structure of a lithium-treated soybean pectin: characteristics of the fragments and determination of the carbohydrate substituents of galacturonic acid

Two galacturonic-acid-containing polysaccharide fractions (ChSS and P) were isolated from soybean meal and subjected to lithium treatment. The fragmen ts obtained were analyzed by using monosaccharide and methylation analyses, and NMR spectroscopy. Lithium degradation of ChSS, followed by sodium boro deuteride reduction, hydrolysis, sodium borohydride reduction, and acetylat ion afforded alditol acetates, of which the labeled ones reflected residues linked to GalA. As followed from quantifications of the labeled and non-la beled alditols from each constituent monosaccharide by GLC-EIMS, 6 mol% of Ara, 22 mol% of Fuc, 13 mol% of Gal, 53 mol% of Rha, and 57 mol% of Xyl are glycosidically linked to GalA. Analysis of the lithium-treated polymer rev ealed that it contains arabinogalactan side chains linked to Rha O-4, which consist of a beta-(1-->4)-linked galactan substituted with highly branched arabinan chains. On average, an arabinogalactan chain contains up to 29 Ga l and 25 Ara residues. Surface plasmon resonance was used to determine cond itions for affinity chromatography. Furthermore, this technique confirmed t he presence of terminal alpha-Fuc residues in ChSS. Polysaccharide P turned out to be relatively resistant to lithium degradation. (C) 2000 Elsevier S cience Ltd. All rights reserved.