The influence of adding monovalent salt on the rheology of concentrated sodium caseinate suspensions and the solubility of calcium caseinate

The effect of adding NaCl or KCl on the rheology of concentrated sodium caseinate suspensions was investigated over a wide range of protein concentrations (40–235 g L−1) and temperatures (10–60 °C). The viscosity increased strongly with increasing protein concentration, due to close-packing of caseinate particles, but decreased with increasing temperature. For protein concentrations ≥80 g L−1, increasing the salt concentration above 0.2 m caused an increase of the viscosity by up to more than two orders of magnitude. Oscillatory shear measurements showed that the suspensions were visco-elastic and that increasing the salt concentration caused an increase of the terminal relaxation time. Calcium ions caused attractive interaction between the caseins and led to the formation of dense protein domains that sedimented on centrifugation. Addition of NaCl led in this case to dissociation of the dense protein domains and increased the solubility of the caseins.