Structural characteristics of water-extractable nonstarch polysaccharides from barley malt

Water-extractable (WE) material was isolated from a Canadian barley malt (cv. Harrington). The purified WE material contained mainly arabinoxylans, beta-glucans, proteins, and small amounts of arabinogalactans and mannose-containing polymers. WE material was treated with specific enzymes to obtain two fractions: one enriched in arabinoxylan (AX) and another enriched in beta-glucan (BG). The AX fraction was further fractionated by stepwise precipitation in (NH4)(2)SO4 into five arabinoxylan subfractions. H-1-NMR spectroscopy and sugar analyses revealed a relatively high content of unsubstituted xylose residues (48-58%) as well as a relatively high content of doubly substituted xylose residues (28-33%) in the structure of the arabinoxylans. beta-Glucans constituted a minor portion of water-extractable malt polysaccharides and were characterized by high levels of tri- and tetrasaccharide residues (93.4%) with a molar ratio of 2.19 for cellotriosyl to cellotetraosyl units. Size-exclusion chromatography revealed that the WE material contained several polymer populations. One population had a very high molecular weight that appeared to be the result of aggregation. The AX fraction contained higher molecular weight polymers than the BG fraction.