The effect of denaturation degree of protein on the microstructure, rheology and physical stability of oil-in-water (O/W) emulsions stabilized by whey protein isolate

The objective of this work was to study the effect of denaturation degree of WPI dispersions used as surfactant on the microstructure, rheology, and physical stability of O/W emulsions. Emulsions with different oil contents (10%, 20% and 30% w/w) were formulated using sunflower oil, as the dispersed phase, and WPI dispersions with different degrees of denaturation (0%, 15%, 30%, 45% and 60%), as continuous phase. The emulsions were characterized in terms of (i) microstructure, quantified by optical microscopy and image analysis, (ii) rheological properties, based on flow curve tests, and (iii) physical stability, evaluated by static multiple light scattering. The diffusional migration of proteins to the oil-water interface was slightly affected by denaturation degree of proteins. Microscopy images of the emulsions revealed that droplet size distribution and mean droplet sizes were strongly affected by the denaturation degree of protein dispersions above 30% and by the oil content at 30%. The rheology of emulsions presented a shear-thinning behavior for all conditions studied. The physical stability of the emulsions increased with an aggregation degree up to 45%, presumably because of the increased apparent viscosity of the continuous phase.