Concurrent phase separation and gelation in mixed oat β-glucans/sodium caseinate and oat β-glucans/pullulan aqueous dispersions

The phase separation behavior of mixed oat beta-glucans/sodium caseinate and oat delta-glucans/pullulan aqueous dispersions at 20 degrees C has been Studied. The concentration of beta-glucans required for induction of phase separation and the physical state of the separated phases, as revealed by visual observations and dynamic rheometry, depended on the molecular weight of beta-glucans and the initial polymeric composition. For beta-glucans with apparent molecular weights (M,) 35 and 65 x 103 the beta-glucan concentration at which thermodynamic incompatibility occurred decreased from about 2-2.5% (w/w) at low concentrations (similar to 0.2%) of sodium caseinate or pullulan to about 1-1.5% (w/w) beta-glucans at high levels (up to 7.5% w/w) of the second biopolymer; these bi-phasic systems consisted of an upper liquid phase and a lower gel-like phase. For beta-glucans with M-w of 110 x 10(3), a bi-phasic system with two liquid phases appeared above a certain beta-glucan concentration, which decreased from approximately 4% to 1% (w/w) with increasing sodium caseinate levels in the range of 0.2-7.5% (w/w). With further increase in beta-glucan concentration, the lower phase turned into a gel, and at even higher beta-glucan concentrations, the polymer demixing process was 'arrested' by chain aggregation events, leading to a macroscopically single gel phase. Generally, the aggregation of beta-glucans seemed to interfere with the phase separation phenomenon resulting in an increase of beta-glucan concentration in the lower phase between 5% and 110% and only a slight increase of sodium caseinate or pullulan concentration in the upper phase (<10%), due to kinetic entrapment of the polymeric components into a highly viscous medium. (C) 2008 Elsevier Ltd. All rights reserved.