Gelation of gellan induced by trivalent cations and coexisting trivalent with monovalent cations studied by rheological and DSC measurements.

The effect of trivalent cation Fe ³⁺ on the gelation process of a sodium salt form of gellan (DG, deacylated gellan gum) was investigated by rheology and DSC studies. On addition of a fairly low concentration of Fe ³⁺ (1 mM), both the complex modulus (G*) of a 1.0 % DG solution in gel state and the sol-gel transition temperature (T _gel ) slightly decreased. At higher Fe ³⁺ concentrations (2 and 3 mM), however, a slight increase in the G* and T _gel was observed. In the coexisting monovalent cation (K ⁺ ) solutions, addition of Fe ³⁺ always improved the G* in gel state and the T _gel in a concentration-dependent manner. Moreover, for all Fe ³⁺ DG solutions, the ordered structure formation temperature (T _order ) was always lower than T _gel and increased with increasing Fe ³⁺ concentration. This finding indicates that the network formation in the DG solutions should occur in advance of the ordered structure formation of the DG chains and that the presence of Fe ³⁺ unfavorably affected the conformational transition of DG. In coexisting cation solution, the presence of K ⁺ ion made a favorable contribution to the binding of Fe ³⁺ to the disordered DG chains and to the subsequent ordered structure formation of the DG chains.
Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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