Structural Characterization and Stability Evaluation of Walnut Oil Oleogel-in-Water High-Internal-Phase Emulsions

Novel high-internal-phase emulsions (HIPEs) were prepared by using plant-based natural ingredients. The oil phase of the HIPEs was gelled using rice bran wax (RBW), and the effect of RBW concentration and emulsifier types (octenyl succinic acid (OSA) starch and soy protein isolates (SPIs)) on the structures and stability of the emulsions was explored. Microstructural observations illustrated that the HIPEs were of the O/W type with tightly arranged droplets. With the increase in the RBW content, the particle size and ζ-potential of HIPEs were decreased gradually. Stability analyses showed that the addition of RBW could effectively improve the storage, freeze–thaw, and lipid oxidation stability of the emulsions. Generally, HIPEs with OSA starch tend to be more stable. Small-amplitude oscillatory shearing tests revealed that the storage modulus of the samples was dependent on RBW concentration. Creep recovery tests indicated that oleogelation strengthened the structures of HIPEs and improved the deformation resistance of the systems. Tribological tests suggested that the addition of RBW increased the coefficient of friction of the emulsions in the mixed and hydrodynamic lubrication regimes. These results demonstrated that oleogelation could improve the stability of HIPEs, and it was of great significance for the development of novel healthy plant-based foods.