On the self-assembly of sodium caseinate

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 degrees C. The polycondensation theory in general provides better fits and indicates low functionality (f ca. 3) at 30 degrees C suggesting non-centrally symmetric growth of aggregates (not within the scope of the AHS (f = infinity) 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) similar to r(-6.75)). Continuous sheer 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. (C) 1999 Published by Elsevier Science Ltd. All rights reserved.