Characterization and Pickering Emulsification of Porcine Plasma Protein Nanoparticles Induced by Mild Acidification and Heat Treatment

To improve the emulsification properties of porcine plasma protein (PPP), this study focused on investigating the physicochemical characteristics and oil-water interface stabilization capabilities of PPP nanoparticles (PPP-NP) formed through thermal treatment under different pH conditions. Firstly, particle size, zeta potential, secondary structure, microscopic morphology, and oil-water interfacial tension reduction capacity of PPP-NP were characterized by the instruments including nanoparticle size analyzer, circular dichroism spectrometer, field-emission scanning electron microscope (FE-SEM) and interfacial rheometer. Subsequently, the Pickering emulsions were fabricated through using PPP-NP as emulsifier, and then the emulsibility and emulsification stability of PPP-NP were evaluated by analyzing the particle size, apparent viscosity, zeta potential, oil droplet morphology of the emulsion during storage. Finally, emulsion stability was quantitatively assessed through a stability analyzer. The results from analyzing the particle size, zeta potential, FE-SEM, interfacial tension indicated that PPP aggregated orderly at pH 6.5, and thereby formed the nanoparticles with an average particle size of about 112 nm and a polydispersity index (PDI) of 0.19. The aggregates were uniform in shape and size and showed good dispersibility and strong capability of reducing oil-water interfacial tension. Compared to the control group, the PPP-NP-stabilized Pickering emulsion displayed high viscosity, relatively large droplet size but better uniformity and storage stability. After 28 days of storage at 45 ℃, the emulsion maintained more uniform droplet distribution. The results from confocal laser scanning microscope (CLSM) combined with backscattered light intensity and Turbiscan stability index (TSI) analysis indicated that the corresponding PPP-NP-based emulsions at pH 6.5 were very stable, and the oil droplets in it were uniform in size without aggregation. The TSI values of the emulsion were relatively low, which were 71.4% lower than that of the control group. Overall, PPP could aggregate orderly and form the nanoparticles with excellent emulsifying properties through heating the solution at pH 6.5, and the finding could provide some valuable insights for the application of PPP as emulsifier in the structural and functional design of food.