Preparation and characterisation of whey protein fluid gels: the effects of shear and thermal history

With the potential use of fluid gels in structuring fluids, whey protein isolate (WPI) was used as a prerequisite to prepare fluid gels: owing to its high nutritional value and thermal stability on gelling. Fluid gels were prepared via heat-induced gelation of a 10 wt% protein solution under controlled temperature and shear. Physical properties of the resulting gel particles (e.g. size and particle–particle interactions) were found to be dependent on the combination of shear and thermal history. Discrete large aggregates (>120 μm) were obtained at low shear, with aggregate size decreasing (<40 μm) at higher shear. Such microstructural changes in the particles led to the control of the suspension rheology. All suspensions showed a marked shear thinning behaviour associated with particle break-up which was observed to be more apparent for larger aggregates, originally made at low shear. The viscoelastic properties of the particulate systems, once in intimate contact (e.g. high volume fraction) resembled a pseudo solid material. In addition, it was shown that at a given volume fraction, the elasticity of the suspension varied dependant on their original processing conditions, owing to the degree of particle–particle interactions. A qualitative model has therefore been presented for the formation of particles by which the rheology is determined.