Effects of Sodium Chloride and Calcium Chloride on the Interaction between Gellan Gum and Konjac Glucomannan

Abstract

Interaction between gellan gum (GELL) and konjac glucomannan (KGM) with and without sodium chloride and calcium chloride has been studied using dynamic viscoelastic measurements and differential scanning calorimetry (DSC). With progressive addition of NaCl, storage shear modulus G‘ and loss shear modulus G‘‘ for mixtures increased, and not only the helix−coil transition temperature of GELL molecules in mixtures but also the sol-gel transition temperature for mixtures shifted to higher temperatures with increasing concentration of salts. In the presence of CaCl2, G‘ increased up to a certain concentration and then decreased with increasing concentration of salts, although the helix−coil transition temperature of GELL molecules in mixtures monotonically increased with increasing concentration of salts. The exothermic and endothermic peak temperatures for mixtures in the cooling and heating DSC curves shifted to higher temperatures with increasing concentration of both NaCl and CaCl2. In the presence of CaCl2, the exothermic enthalpies for mixtures showed a maximum at a certain concentration and then decreased with increasing concentration of CaCl2. KGM is attached to the surface of large aggregates of GELL helices, and since cations promote GELL self-aggregation by a screening effect, the synergistic interaction between GELL and KGM was promoted with increasing concentration of salts. However, sufficient CaCl2 formed various aggregates of GELL helices with different thermal stabilities, so that the phase separation in GELL/KGM mixtures was promoted in the presence of sufficient CaCl2. Keywords: Gellan gum; konjac glucomannan; rheology; differential scanning calorimetry; helix−coil transition; sol−gel transition; salts