Evidence of intermolecular associations of β-glucan and high-molar mass xylan in a hot water extract of raw oat groat

Abstract

High molar mass (HM) β-glucan present in oat products can reduce the risk of diet-related diseases, mainly owing to significantly increased digesta viscosity in human small intestine. To verify a research hypothesis that arabinoxylan (AX) present in oat water extract is associated with HM-β-glucan and thus may influence its functionality, multi-detection HPSEC coupled with enzymatic hydrolysis, sugar and 1H NMR analyses were performed. Isolated cell wall polysaccharide fraction comprised branched AX (arabinose-to-xylose ratio, Ara/Xyl ~ 0.8) and arabinogalactan-protein (AG-P). Nevertheless, it contained (10%) unbranched HM-xylan subfraction (weight-average molar mass, Mw ~ 3153 kg/mol), which was aggregated with β-glucan (Mw ~ 1029–1589 kg/mol) through its HM cellulose-like region. Of the two low molar mass-AXs (LM-AXs) isolated, the first having C(O)-3-monosubstituted and C(O)-2,3-disubstituted β-d-xylopyranosyl residues was covalently interlinked to HM-xylan. The second highly feruloylated, containing C(O)-3- and C(O)-2-monosubstituted units, was tightly bound to AG-P with terminal and 5-linked α-L-arabinofuranosyl residues, and non-covalently associated with LM-β-glucan subfraction.