On the self-assembly of sodium caseinate

Abstract

Abstract A detailed study of the concentration dependence of the osmotic pressure of sodium caseinate solutions encompassing the dilute, semi-dilute and highly concentrated regimes is presented. For the semi-dilute regime, assuming the model of sub-micelles forming `association polymers', the data is considered in relation to the adhesive hard sphere (AHS) model and an adapted f -functional polycondensation theory. The AHS model fits reasonably at higher temperatures but is unsatisfactory at 30°C. The polycondensation theory in general provides better fits and indicates low functionality ( f ca. 3) at 30°C suggesting non-centrally symmetric growth of aggregates (not within the scope of the AHS ( f =∞) model), a prediction supported by EM studies. Both models suggest small sub-micellar building blocks of diameter ca. 11 nm and aggregation number 4–5 with implicit voluminosity comparable to that of native casein sub-micelles. To represent the behaviour in the highly concentrated regime, above close packing of the sub-micelles, a rigid lattice model is proposed which suggests `soft sphere’ potentials for the sub-micelles ( V ( r )∼ r −6.75 ). Continuous shear rheology, contrasted with the Krieger–Dougherty hard sphere prediction, shows the expected sensitivity to aggregation at low phase volumes and to particle softness above close packing.