Oil-water interfacial behavior of zein-soy protein composite nanoparticles in high internal phase Pickering emulsion

We investigated the interfacial properties of zein-soy protein isolate (SPI) composite particles (ZSCPs) at the oil-water (O/W) interface through pH-shift treatment, along with the preparation and stability of high internal phase Pickering emulsions (HIPPEs). Fourier transform infrared spectroscopy (FTIR), three-dimensional fluorescence, and scanning electron microscopy (SEM) revealed hydrogen bonds and hydrophobic interactions within ZSCPs, altering their structure based on mass ratios. Increasing SPI content in ZSCPs decreased particle size, dynamic interfacial tension (γ), and molecular entanglement, promoting diffusion, penetration, and rearrangement processes. Zein particles (ZPs) exhibited fast diffusion and penetration rates due to higher surface hydrophobicity (H0) and lower zeta potential, while rearrangement was hindered. ZSCPs formed viscoelastic films at the O/W interface, strengthened by SPI. Protein films displayed strain softening during extension in the dilatational measurement under relatively large amplitude (>20%). However, during compression at large amplitude, the protein particle with zein to SPI mass ratios of 10:0 and 7:3 interface films showed strain hardening, while 5:5, 3:7 and 0:10 strain softening. HIPPEs stabilized by ZSCPs showed enhanced interface performance, ensuring long-term stability (upto 30 days). These findings offer new prospects for ZSCP applications in food emulsions, while enhancing our understanding of protein particle adsorption at the O/W interface.