Proteins at interfaces and in emulsions Stability, rheology and interactions

Abstract

Physical properties of oil-in-water emulsions stabilized by milk proteins are determined largely by the nature of the adsorbed layer at the surface of the dispersed droplets. There are two distinct classes of protein: the disordered caseins (especially α_s1-casein and β-casein) and the globular whey proteins (especially β-lactoglobulin). Substantial differences exist between these two classes in terms of adsorbed layer structure and surface rheological properties at the oil/water interface. Theoretical modelling of adsorbed layers of α_s1-casein and β-casein with a simple self-consistent-field approach is useful for understanding the excellent stabilizing properties of the caseins, and in interpreting the aggregation behaviour of casein-based emulsions as a function of ionic strength and pH. The creaming behaviour and droplet flocculation are sensitive also to the concentration of non-adsorbed casein. In systems containing milk protein and small-molecule surfactant, competitive adsorption has a strong influence on orthokinetic emulsion stability, and on the viscoelasticity of heat-set β-lactoglobulin-stabilized emulsion gels. Computer simulation of model particle gel networks shows considerable promise for providing new insight into the relationship between interparticle interactions and the structure and rheology of emulsion gels.