Effects of pH and temperature on colloidal properties and molecular characteristics of Konjac glucomannan

The hydrocolloidal characteristics of Konjac glucomannan (KGM) are important for its application as a thickening and gelling agent for liquid foods. In this study, the rheological behavior and molecular properties such as molar mass, hydrodynamic radius and chain conformation of KGM in water were determined at various pH levels (4.0-10.0) during heating from 20 to 80 °C. Acidic and neutral conditions (pH 4.0-7.0) promoted the dispersion of KGM, and alkaline condition at pH 10 favored its aggregation in water, while KGM maintained a random coil conformation in the whole pH range. Associated with the pH effects were changes in the rheological behavior during heating from 20 to 80 °C. The significant differences in the colloidal and rheological characteristics were mainly attributed to alteration of intermolecular interaction (attractive or repulsive) rather than deacetylation at various pH levels. Deacetylation occurred in both acidic and alkaline condition. The second virial value was positive in acidic and negative in alkaline condition. The results showed that hydrocolloidal characteristics of KGM in water were significantly affected by pH.