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Structural Characteristics of Water-Extractable Nonstarch Polysaccharides from Barley Malt¹

¹Contribution No. 824 of the Grain Research Laboratory, Canadian Grain Commission, 1404-303 Main Street, Winnipeg, Manitoba R3C 3G8, Canada. ²Department of Nutritional Evaluation of Plant Materials, Institute of Plant Breeding, Radzikow, 05-870 Blonie, Poland. ³Grain Research Laboratory, 1404-303 Main Street, Winnipeg, Manitoba, R3C 3G8 Canada. ⁴Corresponding author: E-mail: mizydorczyk@cgc.ca Phone: 204-983-1300. Fax: 204-983-0724.

Water-extractable (WE) material was isolated from a Canadian barley malt (cv. Harrington). The purified WE material contained mainly arabinoxylans, β-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 β-glucan (BG). The AX fraction was further fractionated by stepwise precipitation in (NH₄)₂SO₄ into five arabinoxylan subfractions. ¹H-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. β-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.