Effects of Ammonium Salts on the Rheological and Thermal Properties of Gellan Gum Gels

Abstract

Differential scanning calorimetry, dynamic viscoelastic and breaking stress measurement were carried out for gellan gum gels containing NH₄I, NH₄Cl, NH₄Br or NH₄F. Breaking stress andstorage shear modulus G' of gellan gum gels containing NH₄I, NH₄Cl and NH4Br increased in proportion to an ammonium salt (0-50mM) concentration. But in the case of gels containing fluoride ions, these increases were only observed for samples with low salt concentration and after the sharp drop of these values, then these increased again. The exothermic peak temperatures accompanying sol-to-gel transitions shifted to higher temperatures with increasing salt concentration. This has been attributed to the shielding of the electrostatic repulsion of carboxyl groups in gellan gum molecules by ammonium ions. In both thermal and rheological properties, gels containing fluoride ions showed different behaviors from those containing iodide, bromide or chloride ions.