Constitution of konjac glucomannan: chemical analysis and 13C NMR spectroscopy

The constitution of konjac glucomannan was determined by methylation analysis and 13C NMR spectroscopy. The results of methylation analysis showed that the branching point is C-6 carbon of glucosyl units. 13C NMR spectroscopy (1D and DEPT) of konjac glucomannan supported the presence of β-C-1-linked C-6 carbon of glucosyl units as the branching units. This result differs from previous investigations. The 13C NMR spectra indicated that the ratio of terminal glucosyl units to terminal mannosyl units is ca. 2 and branching frequency is ca. 8%, supporting the results by Smith et al. From the splitting of main chain signals the sequences of glucosyl and mannosyl units in konjac glucomannan are estimated and a model structure for the glucomannan is proposed.