Structural features of water soluble (1,3) (1,4)-β- d-glucans from high-β-glucan and traditional oat lines

Abstract

Information on structural features of β-glucans purified from a traditional (4.4% β-glucan) and two high β-glucan oat lines (6.0 and 7.3%) was obtained by partial and complete hydrolysis with lichenase. The depolymerization process was monitored with disodium 2,2′-bicinchoninate reductometry (BCA), fluorophore-assisted capillary-electrophoresis (FACE) and nuclear-magnetic-resonance spectroscopy (NMR). The average degree of polymerization (DP) of the completely hydrolyzed β-glucans was the same for β-glucans from the three oat lines, as determined from NMR spectra (3.7), by FACE (3.4), and by BCA (3.9). By FACE, the β-glucans from all three lines had the same molar ratio of cellobiosyl-(1,3)- d-glucose/cellotriosyl-(1,3)- d-glucose units of 1.6. By NMR the ratio of β (1,4)/β(1,3) before hydrolysis was 2.4 and after complete hydrolysis 1.7, with no significant differences among oat lines. Identical molar ratios of penultimate oligosaccharides (DP6, DP7 and DP8) released during partial depolymerization suggested the same arrangement of cellotriosyl/cellotetraosyl residues in the β-glucan polymers from normal and high β-glucan oat lines. Differences in lichenase specificity toward the β-glucans from the three sources, however, were observed during partial depolymerization, which were attributed to differences in chain lengths of the three polymers. The preferred substrate was the polymer with the highest initial DP. A more limited specificity was observed for the β-glucans with the lowest initial DP.