Confined flow behavior under high shear rates and stability of oil/water high internal phase emulsions (HIPEs) stabilized by whey protein isolate: Role of protein concentration and pH.

High shear rheometry was used to investigate the rheological behavior of high internal phase emulsions (HIPEs) stabilized by whey protein isolate (WPI). The physical stability of HIPEs was tested at extremely high shear rates generated by decreasing the gap height between parallel plates. Viscosity and yield stress, at narrow gaps, increased with protein concentration due to tighter packing of smaller droplets. Structural breakdown and recovery of HIPEs were affected by protein concentration and pH. The hysteresis behavior of HIPEs was either thixotropic or anti-thixotropic and was determined by protein concentration, whereas pH affected the magnitude of anti-thixotropy. At pH 3, emulsions showed greater stability against extreme shear and creaming due to higher deformability of oil droplets and increased interdroplet interaction compared to neutral pH. Challenging the physical integrity of concentrated emulsions under high shear is an effective way to characterize microstructural changes and stability of HIPEs in foods.