Nuclear Magnetic Resonance and Methylation Analysis-Derived Structural Features of Water-Extractable Arabinoxylans from Barley (Hordeum vulgare L.) Malts

Water-extractable arabinoxylans (WEAX) were precipitated with ethanol (65%, v/v) in water extracts of six barley malts. The precipitates consisted of 82−89% arabinoxylan (carbohydrate basis) with arabinose to xylose ratios from 0.60 to 0.76. The WEAX recovered represented up to 50% of all WEAX present in barley malt (43−49.5%). Methylation analysis of these WEAX showed a low proportion of O-3 monosubstituted xylose residues (5.1−7.1%), a high proportion of disubstituted xylose residues (24.8−28.0%), and the presence of O-2-monosubstituted xylose residues (5.1−6.8%). Relative proportions of unsubstituted, monosubstituted, and disubstituted xylose resulting from the methylation analysis were confirmed by 1H-nuclear magnetic resonance (1H-NMR) spectral data. Calculations from 1H-NMR spectral data appear to overestimate the level of O-2-monosubstituted xylose residues. Size exclusion chromatography could not reveal significant differences in WEAX molecular weight profiles between the six malts. The molecular weight profiles showed a peak at about 38 kDa. Keywords: Arabinoxylan; barley malt; structure; nonstarch polysaccharides