Synergistic effects of ultrasound, pH-shifting and transglutaminase on high internal phase pickering emulsion stabilized by whey protein isolate microgel particles.

Protein-based particle-stabilized high internal phase Pickering emulsion gels (HIPPEGs) are gaining interest for their potential in stable, functional, and reduced-fat food products. Whey protein isolate microgels (WPIMs), as natural emulsifiers, are particularly promising; however, the combined effects of transglutaminase (T), ultrasonic (U), and pH-shifting (P) treatments on their functionality remains underexplored. The aim of the current study was to investigate the impact of U, P, and T treatments on the structure and characteristics of HIPPEGs. UPT treatment increased the α-helix and β-sheet content of WPIM from 23.1 % to 30.8 % and 34.5 % to 41.7 %, respectively. Its interfacial tension decreased from 37.2 mN/m to 19.4 mN/m, and its particle size reduced from 204.5 nm to 135.7 nm. The zeta potential of -44.67 mV indicated enhanced particle stability. Rheological analysis revealed UPT-treated had the highest storage modulus (4.52 Pa), stronger gel networks, and greater gel hardness (5.3 N). Enhanced thermal and centrifugal stability further confirmed their superior structural integrity. Super-resolution microscopy showed uniform, smaller droplets in UPT-treated, with steric hindrance preventing aggregation. Overall, UPT-modified WPIMs are promising for designing stable HIPPEGs applicable to high-fat foods, functional emulsions and reduced-fat products. Further studies may explore their in vitro digestion, release behavior, and long-term storage stability.