Effects of pH on ultrasonic-modified soybean lipophilic protein nanoemulsions with encapsulated vitamin E

Soybean lipophilic protein (LP) is a promising emulsifier for nanoemulsion delivery systems. Herein, the influence of pH on the stability, rheological properties, and encapsulation efficiency of a nanoemulsion formed by ultrasonically modified LP was determined, and its influence mechanism was explored. The delivery system exhibited a high absolute zeta potential value (18–30 mV) in neutral and alkaline environments (pH 7.0 or 9.0) and uniform particle size distribution (100–350 nm). Cryo-scanning electron microscopy showed that LPs in neutral and alkaline environments covered the oil–water interface more evenly than those in acidic environments. Moreover, the LP nanoemulsion has excellent rheological properties and exhibit high emulsification performance, vitamin E encapsulation efficiency, and oxidation stability. These improvements occurred because the nanoemulsion prepared using ultrasonicated LP had a high absolute zeta potential value (maximum 30 mV), small droplet size (minimum 190 nm), uniform protein film , high viscosity, and good viscoelasticity in different pH environments. In summary, the nanoemulsion delivery system prepared by LP ultrasonication can resist the influence of different pH environments and maximize the delivery efficiency in neutral and alkaline environments. The research results identified a suitable pH environment for LP nanoemulsions and provide a theoretical reference for their further application.