Physicochemical properties and structural characterization by two-dimensional NMR spectroscopy of wheat β-D-glucan -: comparison with other cereal β-D-glucans

The first isolation, purification and characterization of a wheat beta-D-glucan is reported. Alkaline extraction of wheat bran prepared by a novel pre-processing gave a non-starch polysaccharide fraction. Purification was carried out by hydrolyzing the arabinoxylans of this fraction with beta-D-xylanase (T. Viride, EC 3.2.1.8), which had no effect on the molecular weight of the beta-D-glucan. The structure of the purified wheat beta-D-glucan was characterized by NMR spectroscopy, and additional structural detail was revealed by hydrolysis with (1 +/- 3)(1 +/- 4)-beta-D-glucan-4-glucanohydrolase (lichenase, EC 3.2.1.73) and analysis of the oligosaccharide reaction products. Direct and long-range homo(H-1/H-1) and hetero- (C-13/H-1) nuclear shift correlations were used to make complete assignments of both the C-13 and H-1 spectra as well as to confirm sequences and linkage sites. The C-13 NMR Spectrum of wheat beta-D-glucan appeared identical to that of other cereal beta-D-glucans, such as those from oat and barley. However, the ratio of 3-O-beta-cellobiosyl- and 3-O-beta-cellotriosyl-D-glucose obtained from wheat beta-D-glucan by lichenase hydrolysis was significantly higher than ratios from other cereal beta-D-glucans (approximately 4, 3 and 2 for wheat, barley and oat, respectively). The predominant molar proportion of trisaccharide (72.4%) from wheat beta-D-glucan suggests that it will have a more regular structure than the other beta-D-glucans, which might be responsible for its greater gelling ability and poorer solubility in water compared to other cereal beta-D-glucans. (C) 2000 Elsevier Science Ltd. All rights reserved.