Oil-water interfaces stabilized by whey protein colloidal particles: Evolution of interfacial rheology during subphase exchanges using simulated digestive fluids

Whey protein aggregates, formed through controlled processing, can function as soft colloidal particles in "Mickering" emulsions, adsorbing at oil–water (O-W) interfaces to form mechanically robust and viscoelastic films. This study aimed to study the interfacial behaviors of whey protein aggregates (WPAs) stabilized O-W interface during subphase exchanges using simulated digestive fluids to explore their potential for modulated lipid digestion. Two WPAs were produced from whey protein isolate (WPI) using distinct heat treatments. They were characterized and further investigated for their adsorption dynamics, interfacial behaviors before, during, and after subphase exchanges with simulated digestive fluids. Compared to the WPI, both WPAs exhibited increased surface charge, hydrophobicity, and altered secondary structures. These physicochemical characteristics significantly influenced their interfacial adsorption dynamics at the oil-water interface. WPAs showed slower diffusion but higher rearrangement rates after unfolding. In the subphase exchange experiment, WPA-laden interfacial films showed higher resistance to mechanical changes compared to the WPI coated film in the simulated gastric phase. However, at the late stage of simulated intestinal phase that is dominated by bile and lipase, differences in mechanical properties emerged. WPA-1, while stable in the gastric phase, was more digestible in the intestinal phase, reflected by a marked decrease in interfacial elasticity. In contrast, WPA-2 showed smaller changes before and after the digestion. Overall, WPAs demonstrated distinct interfacial and digestion-related behaviors compared to WPI, suggesting their potential in developing emulsions for targeted nutrient delivery. Future work will investigate the correlation between interfacial dynamics and actual lipid digestion outcomes to optimize the use of dairy protein particles in functional food systems. • Two types of colloidal whey protein aggregates (WPA) were manufactured using acidic commercial whey protein isolate (WPI). • The two types of WPA dispersions exhibited acceptable sedimentation stability and distinct interfacial behaviors. • WPA-laden oil-water interfacial film may be explained by Mickering stabilization mechanism. • The mechanics of WPA-laden films were more resistant to change upon treatment of simulated gastric fluid compared to WPI . • WPA as an Mickering stabilizer can modulate interfacial rheology dynamics during a series treatment of simulated gastric and intestinal fluids, respectively.