Phase behaviour of oat β-glucan/sodium caseinate mixtures varying in molecular weight

The isothermal phase behaviour at 5 degrees C of mixtures of sodium caseinate and oat beta-glucan isolates varying in molecular weight (MW) was investigated by means of phase diagram construction, rheometry, fluorescence microscopy and electrophoresis. Phase diagrams indicated that the compatibility of the beta-glucan/sodium caseinate system increases as beta-glucan MW decreases. Images of mixtures taken at various biopolymer concentrations revealed phase separated domains. Results also revealed that at the state of thermodynamic equilibrium, lower MW samples yielded considerable viscosity in the mixture. At equivalent hydrodynamic volume of beta-glucan in the mixtures, samples varying in molecular weight exhibited similar flow behaviour. A deviation dependent on the protein concentration was observed for the high MW sample in the concentrated regime due to the size of beta-glucan aggregates formed. Results demonstrate that by controlling the structural features of beta-glucan in mixtures with sodium caseinate, informed manipulation of rheological properties in these systems can be achieved. (C) 2012 Elsevier Ltd. All rights reserved.