Abstract
Three fractions containing hemicellulosic material were obtained by sequential extraction of barley residue (left after removal of water-extractable polysaccharides) with saturated barium hydroxide [Ba(OH) 2 fraction], distilled water [ Ba(OH) 2 H 2O fraction], and 1 m sodium hydroxide [NaOH fraction]. The yields of the fractions were 1.6, 1.7, and 2.6% (w/w), respectively, of the dry barley grist. The Ba(OH) 2 fraction contained mainly arabinose and xylose, 35.8% and 60.9%, respectively. The Ba(OH) 2 H 2O fraction in addition to 26.7% Ara and 36.6% Xyl contained also 34.8% Glc. The NaOH fraction was composed of 14.2% Ara, 44.0% Xyl, and 40.9% Glc. The Ba(OH) 2 H 2O and NaOH extracts were further fractionated by stepwise (NH 4) 2SO 4 precipitation into several subfractions with varying amounts of β-glucans and arabinoxylans. β-Glucans in Ba(OH) 2 H 2O and NaOH fractions were characterized by high ratios of β-(1→4) β-(1→3) linkages, large amounts of contiguously linked β-(1→4) segments, and high ratios of cellotriosyl/cellotetraosyl units. The alkali-extractable arabinoxylans, especially those NaOH-extractable, were characterized by a very low degree of substitution, high xylose arabinose ratio, and a small content of doubly substituted xylose residues. Some populations of arabinoxylans displayed structural features that would enable them to self-associate or to interact with β-glucans.
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