Preparation, process optimisation, stability and bacteriostatic assessment of composite nanoemulsion containing corosolic acid

Corosolic acid (CA), a pentacyclic triterpenoid, exhibits remarkably low hydrophilicity, restricting its application in aqueous systems. To enhance its hydrophilicity, we optimised nanoemulsion preparation conditions, resulting in a stable corosolic acid nanoemulsion system. By screening the oil phase, surfactant, and cosurfactant, along with investigating the mass ratio of surfactant and cosurfactant and the preparation temperature, we achieved an optimal corosolic acid nanoemulsion. We measured the particle size, polydispersity coefficient, and Zeta potential of the optimised formulation. The nanoemulsion's sustained-release effect, stability, and antibacterial activity were subsequently examined. The optimised formulation comprised ethyl oleate, cremophor EL, and Tween 80 (1.5:1), combined with ethanol in a ratio of 1:9:2.25 (w/w/w), and was prepared at 30 °C. This optimised corosolic acid nanoemulsion exhibited uniform particle size distribution, favourable dispersion, and notable slow-release capabilities. Importantly, the nanoemulsion demonstrated exceptional stability. In comparison to the positive control's bacteriostatic zone diameter, it was evident that the CA nanoemulsion (1.06 ± 0.11 mm) and blank nanoemulsion (1.03 ± 0.05 mm) both displayed notable inhibitory activity against <i>S. aureus</i>. Our findings established a solid foundation for the potential application of CA nanoemulsion in the food, cosmetics, and pharmaceutical industries. However, the application of CA nanoemulsion in real food or drug systems has not been explored yet.