Olive oil-in-water high internal phase Pickering emulsions stabilized by hydroxyapatite nanoparticles

Biocompatible high internal phase emulsions (HIPEs) have attracted much attention in food and cosmetics due to their unique properties, such as adjustable viscoelasticity, high nutrient load, and long shelf life. Herein, we report an olive oil-in-water high internal phase Pickering emulsion (HIPE) stabilized solely by bare hydroxyapatite (HA) nanoparticles. Compared with other HIPEs, the HIPEs stabilized by HA nanoparticles could be obtained through a one-step emulsification method without chemical modification or other chemical additives. The increase of HA concentration (≥ 0.5 wt%) resulted in increases in both the storage modulus and loss modulus of the HIPEs, indicating the particle network plays an essential role in the HIPEs gel strength. After increasing the oil phase fraction from 80% to 90%, the viscosity of the HIPEs increased from 8316 to 13855 Pa⋅s (shear rate 0.004 s−1) and exhibited as a pseudoplastic fluid. The effect of oil type on the HIPEs was also investigated. The HA nanoparticles may interact with the olefin and carbonyl groups of olive oil, forming interfacial-active particles to stabilize the HIPEs. This method is universal as it occurs with other natural oils (soybean, sunflower, and fish oil), which may have various applications in food, cosmetics, and functional material fields.