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 H-1-nuclear magnetic resonance (H-1-NMR) spectral data. Calculations from H-1-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.