A solid state NMR study of locust bean gum galactomannan and Konjac glucomannan gels

This paper describes a 13C solid state NMR study of hydrated powders and gels of locust bean gum galactomannan-LBG and Konjac glucomannan-KGM. Changes in relative spectral intensities, cross-polarization dynamics (TCH, T1ρH) and relaxation times (T1C, T1H, T2H) show that hydration (0-90%) of LBG powders increases the 108 Hz frequency molecular motions, probably reflecting the enhanced motion of non-aggregating segments and chain ends. Slower motions (104-105 Hz) are enhanced only slightly at 90% hydration. LBG gel shows higher spatial distinction between aggregated and non-aggregated segments than the hydrated powder and relaxation times indicate higher mobility for galactose-ramified segments, compared to linear mannose segments. While the dynamics of KGM hydration is similar to that of LBG, i.e. mainly affecting fast 108 Hz motions, the gel is significantly more rigid. Both spectra and relaxation times show that glucose residues in KGM gel are particularly hindered, probably due to their preferential involvement in chain aggregation.