The Effect of Added Salt on Gelation by Divalent Metal Ions of Alginate Aqueous Solution

Abstract

The alginate is an anionic polysaccharide which is composed of 1, 4-linked p-o-mannuronic acid (M) and 1, 4-linked a-L-guluronic acid (G). It is well-known that a sodium alginate aqueous solution forms a gel by introducing divalent metal ions. In the present study, the effect of added salt on the gelation by divalent metal ions is investigated by way of rheological measurements using a cone-plate type rheometer at 25° C. The salt concentration required for gelation of the alginate aqueous solution increases in the following order; SrCl₂<CaCl₂<MgCl₂. This result is strongly related to the fact that the affinity of divalen t metal ions for the alginate decreases in the following order; Sr²⁺> Ca²⁺> Mg²⁺.