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

摘要

This paper describes a ~(13)C 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 (T_(CH),T_(1rhoH)) and relaxation times (T_(1C),T_(1H),T_(2H)) show that hydration (0-90%) of LBG powders increases the 10~8 Hz frequency molecular motions,probably reflecting the enhanced motion of non-aggregating segments and chain ends.Slower motions (10~4-10~5 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 10~8 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.