Preparation and rheological properties of whey protein emulsion fluid gels

A shear-gel approach was used to coat an O/W emulsion with a whey protein shell. Mechanical shear was applied to an aqueous solution of whey protein isolate (WPI) and oil then heated through the sol-gel transition. The formation of a continuous WPI network was prevented through the shear flow, resulting in discreet spherical capsules, with sizes in the micron scale (similar to 25 mu m). Through careful control over both the oil and WPI components, encapsulation efficiencies of up to 99% were obtained. Subsequent rheological properties highlighted elastic behaviour (G') dependent on oil content; where higher oil fractions increased the effective phase volume of the particles. The result was packing fractions that exceeded those for hard spheres (>0.64), leading to pseudo-solid characteristics at rest, apparent yield stresses and thixotropic behaviour under shear. As such, emulsion fluid gel (EmFG) rheology was closely comparable to those of soft microgel suspensions (fluid gels) and soft-coated particles.