WHEY PROTEIN ISOLATE MICROGELS TAILORING THE HIGH INTERNAL PHASE PICKERING EMULSIONS PROPERTIES

Whey protein isolate (WPI) has been acknowledged for its high nutritional value and outstanding functional properties. In addition to the use of biomolecules attributing all-natural labeling, another strategy applied towards the development of healthier food products is to reduce their lipid content. In essence, high internal phase emulsions (HIPEs) appear as a promising alternative due to their exceptional texture properties and kinetic stability. Herein, we explored the formation of conventional and Pickering HIPEs, stabilized by native protein and derived microgels, respectively. Microgels were prepared by heat-induced aggregation of WPI at different pH's (5.7; 5.9; 6.1 and 6.3) and characterized by their particle size distribution, zeta potential, morphology, and interfacial properties by tracking interfacial tension decay and dilational rheology. These colloidal particles were further applied to HIPEs formation with 0.8 of volume fraction of oily dispersed phase using a rotor-stator homogenizer. Emulsions were evaluated by their droplet size distribution, stability and mechanical properties assessed by rheological measurements. The WPI microgels presented a spherical shape (depicted by cryogenic scanning electron microscopy), and comparable particle size (100-300 nm) and zeta potential values (-20.5±1.0 to -27.2±4.0 mV), regardless of the pH condition of particle’s preparation. WPI microgels promoted a limited interfacial tension decay and a more viscous interface (lower complex modulus) compared to the behavior of the native protein. It suggests that the insoluble protein aggregates undergo lower dynamics events at the interface compared to the soluble native WPI. Highly stable O/W HIPEs were successfully prepared, showing multimodal droplet size distribution and densely packed droplets. Different droplet size populations can be related to the sharp system’s viscosity increase during droplet formation. Rheological measurements confirmed the gel-like properties of emulsions and a more structured emulsion was formed with microgels prepared at higher pHs, decreasing the initial viscosity values (pH 6.3> pH 6.1> pH 5.9> pH 5.7>native) when pH shifted towards the isoelectric point of WPI. However, the more structured the emulsion, the lower the viscosity recovery observed (less thixotropic nature) when samples were subjected to alternating intervals of low and high shear rates. Moreover, accelerated stability tests revealed that the emulsions prepared with microgels fabricated at higher pHs also showed better results. The colloidal form of proteins tailored their behavior at the interface also affecting the properties of the emulsions. Interestingly, the pH of protein solution for microgels preparation did not affect their physicochemical nor interfacial properties but led to changes in HIPEs’ mechanical properties. All the gathered outcomes show the potential of exploring conventional and Pickering WPI-stabilized HIPEs as a texture-provider system with application as an alternative for fat replacers.