Effects of temperature and pH on interfacial viscoelasticity, bulk rheology and tribological properties of whey protein isolate-stabilized high internal phase emulsions

Acidic WPI preheated at 80 °C (30 min) underwent reversible denaturation and formed similarly viscous-dominant interfacial layers as unheated WPI films at pH 3, which led to similar emulsion stability, large amplitude oscillatory shear (LAOS), and tribological character in high internal phase emulsions (HIPEs). Preheating at 95 °C (30 min), however, shifted the response of interfacial layers from viscous-to elastic-dominant due to enhanced inter-protein interactions through irreversible denaturation. The respective HIPEs became stiffer and more stable with less energy dissipated by friction and increased nonlinear response. At pH 7, heating had a more significant impact on the bulk properties of HIPEs rather than their interfaces. This work provides new insight into the relationships between interfacial and emulsifying properties of WPI under different heating and pH conditions. Such knowledge can be used to select optimal processing parameters for tunable textures and predict the structural and functional behavior of food emulsions.