Microstructural changes during alkali- and heat induced gelation of konjac glucomannan

Abstract

We investigate structural changes of konjac glucomannan (KGM) during heat induced gelation of pre-deacetylated samples. We combine rheology at higher concentrations, with light scattering and AFM studies on low concentration samples. Macroscale rheology demonstrates that gelation requires both heat and alkali-induced deacetylation. With Dynamic Light Scattering (DLS) we investigated the time evolution of KGM particle hydrodynamic radius (Rh) during the deacetylation reaction. Before deacetylation we observe that heating leads to swelling of the KGM particles in solution. From the kinetics of particle aggregation, we deduce that deacetylation itself is the rate-determining step and that aggregation occurs immediately after deacetylation. In Atomic Force Microscopy (AFM), native KGM particles appear as compact globular objects. Consistent with the light scattering results, we observe that heating leads to opening and swelling of these particles, and that deacetylation leads to their interaction to each other into a network. Our DLS and AFM results help understand the microscopic origins of heat- and alkali-induced gelation of KGM.