C-13 NMR characterization of molecular structures in powders, hydrates and gels of galactomannans and glucomannans

Molecular structures present within powders, hydrates and gels of a range of galactomannans have been probed using high-resolution C-13 NMR spectroscopy in both solid and solution states. As reference materials, ivory nut mannan (strong X-ray diffraction pattern of the mannan I polymorph) and gelled de-acetylated konjac glucomannan (weak mannan II diffraction pattern) have been utilized. Comparison of C-13 spectral features suggests that hydrates, solutions and gels of galactomannans all contain mannan conformations similar to those in glucomannan gels. Chemical shift features characteristic of the mannan I form are observed for a dried and milled low-galactose galactomannan, although these features do not persist upon hydration. Dry powders of galatomannans have broad resonances probably due to the presence of a range of conformational states. Comparison of 'solid-like' and 'solution-like' spectral features in gelled samples suggests that relatively rigid chain segments are enriched in mannosyl residues for locust bean galactomannan and glucosyl residues of konjac glucomannan respectively.