Observation of Molecular Chains of Hydrolyzed Konjac Glucomannan by Scanning Probe Microscope

Abstract

Konjac glucomannan (KM) is a water soluble glucomannan with high molar mass. KM aqueous solution shows extremely high viscosity. KM can be depolymerized by chemical hydrolysis. The molar mass of hydrolyzed KM decreased with increase of hydrolysis time. The acid hydrolysis led chain scission of KM, but introduced no significant new chemical groups into the structure. The weight-averaged molar mass,M_w, of original KM and that of 30 min hydrolyzed KM were 1.0 x 10⁶ Da and 6.0 x 10³ Da, respectively. The weight-averaged radius of gyration, R_G, of original KM was 98.0 nm. The R_G value decreased with increase of hydrolysis time and then reached to below 10 nm at 20 min of hydrolysis time. SPM image of original KM molecular chain showed string-like pattern. The contour length and the chain height of original KM were 1193 nm and 1.2 nm, respectively. The chain height scarcely changed regardless of molar mass, but the contour length decreased significantly with increase of hydrolysis time. The chain lengths of KM with M_w of 5.9 x 10⁵Da and 1.8 x 10⁵ Da were 688 nm and 268 nm, respectively.