Preparation of high internal phase Pickering emulsions stabilized by egg yolk high density lipoprotein: Stabilizing mechanism under different pH values and protein concentrations

While egg yolk high-density lipoprotein (HDL) is a potential stabilizer for preparing high internal phase Pickering emulsions (HIPPEs), its poor solubility and stability are the critical challenges to overcome. In this work, soluble HDL was obtained from dissolving egg yolk granules and removing phosvitin. HIPPEs were prepared by HDL as a sole stabilizer with a simple homogenization method. The results showed that HDL self-assembled with small amount of LDL into micellar structure in solution, along with an isoelectric point between pH 6 and 7. As expected, the emulsifying ability showed a strong correlation with the pH conditions and HDL concentrations. HIPPE that was prepared at pH 5 exhibited small droplet size, high viscosity and gel stability. When the pH values were above 6, unstable double HIPPEs formed because the continuous increment of contact angles of HDL induced the emulsion phase transformation. After storage for 3 d, the number of droplets of as-formed double HIPPEs was significantly reduced, along with increment in droplet size and conversion of single HIPPEs. Our findings in this study are of importance for not only using egg yolk HDL to prepare food-grade HIPPEs, but also investigating the stability mechanism of the protein-based nanoparticles at oil-water interface.