Isolation and characterization of water-extractable arabinoxylan from hull-less barley flours

A new procedure was developed for the isolation of highly purified water-extractable arabinoxylan (WE-AX) from hull-less barley flour. It included inactivation of endogenous enzymes, removal of proteins with silica gel, and removing beta-glucans, arabinogalactan-peptides, and starch fragments by enzyme or solvent precipitation steps. WE-AX recovered by this isolation procedure represented, on average, 47% of all WE-AX present in hull-less barley flour. Purified WE-AX from flour of different hull-less European barley cultivars contained 84.9-91.8% AX and showed small structural differences. The apparent peak molecular weight of the purified WE-AX was 730,000-250,000, and the arabinose-to-xylose ratio was 0.55-0.63. Proton nuclear magnetic resonance spectroscopy showed that the levels of un-, O-2 mono-, O-3 mono-, and O-2,O-3 disubstituted xylose residues were 59.1-64.7%, 8.2-10.0%, 5.7-10.6%, and 17.6-23.1%, respectively, and the ratio of di- to monosubstituted xylose was 0.90-1.54. Both O-3 mono- and disubstituted xylose residues occurred isolated or next to disubstituted xylose residues in the WE-AX chain.