Low density lipoprotein-pectin complexes stabilized high internal phase pickering emulsions: The effects of pH conditions and mass ratios

The present work aimed to explore the feasibility of using egg yolk low density lipoproteins (LDL) as naturally occurring nanoparticles to prepare high internal phase Pickering emulsions (HIPEs), and to understand the role of pectin (PE) as a natural food thickener in improving the emulsifying stability. Colloidal complexes were formed spontaneously via electrostatic interactions upon mixing PE and LDL at acidic pH condition. The colloidal characteristics of LDL-PE complexes were studied by dynamic light scattering method, Fourier transform infrared spectroscopy and viscosity measurements, as well as interfacial activities. Lastly, the capability of complexes as stabilizers to prepare HIPEs was then comprehensively investigated as functions of pH conditions and mass ratios of LDL and PE. The results indicated that the particle sizes and surface activities of LDL-PE complexes were highly dependent on the electrostatic interactions. The interactions between LDL and PE slightly reduced at neutral pH conditions or higher concentrations of PE, which were more favorable to form stable particles with smaller size and higher surface activity, and thus greater stability of HIPEs. Although the interfacial tensions of LDL increased with the existence of PE, the stability of LDL-PE stabilized HIPEs (LP-HIPEs) was greatly enhanced compared with the free LDL stabilized ones (L-HIPEs). LDL and PE formed non-covalent network among the emulsion droplets and the oil-water interface of HIPEs, inducing stable gel structure. Droplet size analysis and morpho-logical observation under optical microscopes together with digital photos revealed the homogenous emulsion droplets in a strong gel geometry. Gel-like elastic network structure was confirmed by rheological measurement, and the thick coating layer of LDL-PE complexes on the oil-water interface was further visualized by confocal laser scanning microscope. Our findings are innovative and offer new opportunities to prepare HIPEs from all natural ingredients for future applications in the food industry.