Monosaccharide composition of commercial Konjac refined powder by using ¹H-NMR and HPLC analyses

Abstract

To establish a qualitative method for the monosaccharide composition analysis of Konjac glucomannan (KGM) in Konjac refined powder by the two techniques, ¹H-NMR (nuclear magnetic resonance) and HPLC (high performance liquid chromatograph). The hydrolyzed samples treated with cellulase in acetate buffer were separated on a HILIC (Hydrophilic Interaction Chromatography) column using an 80％ acetonitrile aq. eluent, and monitored on a refractive index (RI) detector. In both analytical methods, good separation was achieved for mannose and glucose and thus the composition of two reducing monosaccharides was obtained successfully. In this experiment, we used four types of commercial Konjac flour products, Akagi Ohdama, Miyama Masari, Tokuto Powder, and Timak Mannan (a specially purified powder of konjac glucomannan which does not have any trimethylamine smells). From HPLC analyses, composition ratio of D-glucose/D-mannose was in the range of 1.02 (±0.09)–1.19 (±0.02). From ¹H-NMR analysis, composition ratio was in the range of 1 : 1.185 (±0.010)–1 : 1.266 (±0.004). Compared with the acid-hydrolyzing method, our procedure has several advantages, such as yielding only small amount of residuals after enzymatic hydrolysis.