The gelling behavior of gellan in the presence of different sodium salts.

It is well known that metal ions have great effects on gelling behaviors of gellan aqueous systems, however, the effects of their co-ions - anions have rarely been studied. Herein, we investigated the effects of four kinds of sodium salts with different anions (NaCl, CH ₃ COONa, Na ₂ C ₂ O ₄ and Na ₃ C ₆ H ₅ O ₇ ) on gelling behaviors of gellan aqueous systems in terms of gelling temperature and gel hardness. It was found that, when [Na ⁺ ] was low (20 mM), the salt with Cl ^- or CH ₃ COO ^- favored the gelling of gellan aqueous systems, while the salt with C ₂ O ₄ ^2- or C ₆ H ₅ O ₇ ^3- took adverse effects probably because C ₂ O ₄ ^2- or C ₆ H ₅ O ₇ ^3- could react with divalent cations (Ca ²⁺ and Mg ²⁺ ) in gellan to form precipitates or chelates and break their interactions with gellan (salt bridges). When [Na ⁺ ] was high (50 or 80 mM), all the four kinds of salts facilitated gelling due to the shielding effects of high concentrations of Na ⁺ on the negative charges along the gellan chains, and followed the order of: Cl ^- > CH ₃ COO ^- > C ₂ O ₄ ^2- > C ₆ H ₅ O ₇ ^3- . This study demonstrates the effects of anion kind of salts on gelling behaviors of gellan aqueous systems and provides references for the application of gellan.
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