Effects of sodium carbonate and potassium carbonate on colloidal properties and molecular characteristics of konjac glucomannan hydrogels

When konjac glucomannan (KGM) molecules are deacetylated under alkaline conditions, the aqueous KGM solution is transformed into a thermally stable gel. In this study, series of Na2CO3-induced and K2CO3-induced KGM hydrogels were prepared by deacetylation using different concentrations (0.1, 0.2, 0.3, and 0.4 M) of alkali. The hydrogels were characterized using texture profile analysis, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy, X-ray diffraction, and rheological property analysis. The data showed that KGM hydrogel formation was facilitated at all the alkali concentrations used. The mechanisms of Na2CO3-induced and K2CO3-induced KGM hydrogels formation differed slightly. The hardness, springiness, chewiness, gumminess, and storage modulus G' of the Na2CO3-induced KGM hydrogels initially increased and then decreased with increasing alkali concentration. However, the values of the corresponding properties of the K2CO3-induced KGM hydrogels increased with increasing alkali concentration. All the data were consistent with the structures observed using SEM. The 0.3 M Na2CO3-induced KGM hydrogel had the highest hardness and storage modulus G', a well-proportioned network structure, and a dense architecture; 0.3 M Na2CO3 was therefore the most suitable modifier for inducing KGM hydrogel formation. (C) 2018 Published by Elsevier B.V.