Eco-Friendly Nanoemulsions of Orange Peel Essential Oil: Surfactant Optimization and Long-Term Colloidal Stability

Orange (Citrus sinensis L.) peel essential oil (OPEO) exhibits strong antioxidant and antimicrobial properties, supporting its potential use in diverse food and pharmaceutical applications. However, its industrial use is limited due to its hydrophobic nature and poor aqueous dispersion. This study developed a nanoemulsion system to overcome this limitation using ultrasonic emulsification with OPEO and sesame oil (SO), which was stabilized by the addition of Tween 20 surfactant. Various oil-to-surfactant ratios (1:1, 1:2, 1:3, and 1:4 v/v) and oil concentrations were evaluated for their effects on droplet size and kinetic stability. The optimized formulation at a 1:4 (v/v) and 80% OPEO in the oil phase showed the smallest droplet size (83.66 nm), low polydispersity index (0.24), and a highly negative zeta potential (-31.93 mV), indicating enhanced physical stability. Kinetic stability was confirmed by centrifugation and long-term storage, with no phase separation observed for up to 60 days. SEM images revealed well-dispersed spherical droplets, and FTIR analysis confirmed the successful interaction and encapsulation of oil components. The nanoemulsion retained pH (7.22 to 6.08) and antioxidant activity (58.80 to 57.50%) during storage. This study addresses the formulation challenges of essential oil nanoemulsions and offers a stable delivery system for potential food and edible coating applications.