Comparative study of the rheology and the structure of sodium and calcium caseinate solutions

The viscosity and the frequency dependent shear moduli of dense calcium caseinate (CaCN) and sodium caseinate (NaCN) suspensions were investigated as a function of concentration (50-300 g L-1) and temperature (10-50 degrees C) at pH 6.7. Both systems form visco-elastic suspensions with a viscosity that increases strongly with increasing concentration and decreasing temperature. An important effect of the counter-ion on the visco-elastic properties was observed that is attributed to the specific binding of calcium, which reduces the electrostatic repulsion and induces a net attractive interaction between caseins. The latter may lead to micro-phase separation as was observed by confocal laser scanning microscopy. Mixtures of NaCN and CaCN were significantly different from pure NaCN if they contained more than 50% CaCN. The equivalence between NaCN with added CaCl2 and CaCN is discussed. (C) 2013 Elsevier Ltd. All rights reserved.