Structural characteristics of arabinoxylan in barley, malt, and beer

Non-starch polysaccharides (NSP) content, partially water-soluble and high-molecular-weight polymers, are related to beer viscosity. Thus, arabinoxylan alone, or synergistically with β-glucan, may be involved in some of the undesirable effects in the brewing process, such as influencing the rate of wort separation. Three malting barley samples were studied to determine glycosyl linkage composition of highly substituted arabinoxylans by analysis of partially methylated alditol acetate (PMAA) sugar derivatives using gas chromatography (GC) and gas chromatography–mass spectrometry (GC–MS). Arabinoxylan, total non-starch polysaccharide and β-glucan levels between all samples were not significantly different (P<0.05). The NSP fractions decreased significantly (P<0.05) during malting and brewing. No apparent differences in arabinoxylan structure were found between malt and beer samples. Structurally, four major glycosyl derivatives, t-Glu-p, 4-Xyl-p, 4-Glu-p, and 2,3,4-Xyl-p, were identified. Arabinoxylans appear to contain randomly branched regions, mostly consisting of an unsubstituted and a double arabinofuranosylated xylose residue. The number of xylose residues O-2,3 disubstituted, and O-2 and O-3 monosubstituted were similar in all varieties.