Influence of shearing on the physical characteristics and rheological behaviour of an aqueous whey protein isolate-κappa-carrageenan mixture

The incompatibility of whey protein isolate (WPI) and Kappa-carrageenan (kappa-car) in aqueous mixtures has been extensively studied under quiescent conditions: however, the effect of shear on segregative phase separation is still not fully understood. The present work reports for the first time quantitatively the effect of shearing on the segregative phase separation behaviour of these two polymers. Demixing was observed at pH 7.0 and 22 degrees C, determining the phase diagram and rheological properties of the mixtures. Phase diagrams were derived after heating and cooling mixes at a constant shear rate (28 s(-1)). The phase behaviour was compared to that of the same mixtures under quiescent conditions. The shearing process affects segregative phase separation, causing a shift in the position of the binodal towards lower concentrations of WPI. The bottom layer contained a higher ratio of WPI while the upper layer was enriched in K-car. The addition of K-car to WPI solutions led to a much stiffer heat-induced gel than that prepared with WPI heated in isolation. The height of the plateau of the final elastic modulus G'(infinity)(t) depends on the position of the system on the phase diagram. Using a selected tie line, the viscosity of different systems measured at 80 degrees C was more influenced by the amount of WPI, than by the K-car concentration. Shear treatment of segregative phase separating systems offer a way to modulate the functional properties of the ingredients and the texture of the final product. (C) 2008 Elsevier Ltd. All rights reserved.