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, CH3COONa, Na2C2O4 and Na3C6H5O7) 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 CH3COO- favored the gelling of gellan aqueous systems, while the salt with C2O42- or C6H5O73- took adverse effects probably because C2O42- or C6H5O73- could react with divalent cations (Ca2+ and Mg2+) 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- > CH3COO- > C2O42- > C6H5O73-. 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.