Physical characteristics of calcium induced κ- carrageenan networks

The presence of an optimum counter-ion concentration in calcium-induced κ-carrageenan gels at low polymer concentrations of 5 and 10 g/l is observed. At approximately the stoicheometric molar ratio of 1 calcium per carrageenan sulphate, a gel with high elastic modulus, high optical clarity and fine network structure is observed. On further increase of counter-ion concentration beyond this optimum, elastic modulus decreases significantly associated with sharp increase in the gels turbidity together with a network characterised with coarse and large-pore mesh. ite complete characterisation of the various gel networks both mechanically by ways of oscillatory and static rheology and optically by turbidimetry and cryo-SEM shows that the extensive structural charge neutralisation of the polysaccharide by divalent calcium ions is responsible for a marked aggregation of the polymer strands reminiscent of precipitation. At lower counter-ion to polymer ratios, onset of gelation might prevent such phase separation.