TEMPERATURE-DEPENDENT STABILITY AND KINETICS OF Citrus x latifolia ESSENTIAL OIL NANOEMULSIONS PREPARED BY LOW-ENERGY EMULSIFICATION

Abstract

Citrus x latifolia essential oil (CLEO) contains volatile monoterpenes with potential applications in food systems. However, its practical use is constrained by low water solubility in aqueous environments. While nanoemulsification has been widely investigated as a strategy for dispersing hydrophobic essential oils, the temperature-dependent stability and kinetic behavior of terpene-rich nanoemulsions produced by low-energy methods remain insufficiently understood. In this context, the present study investigated the formation and storage stability of CLEO oil-in-water nanoemulsions prepared by spontaneous emulsification using Tween 80 as the surfactant and propylene glycol as the co-surfactant. Specifically, the formulation consisted of 16% Tween 80, 16% propylene glycol, and 4% CLEO, resulting in nanoemulsions with mean droplet diameters of approximately 16-17 nm, a polydispersity index (PDI) of 0.2-0.3, and an optical transmittance of about 98%. These results indicate a relatively narrow droplet size distribution and high dispersion clarity. To further evaluate stability, temperature-dependent storage experiments were conducted at 10, 30, and 40 °C for 40 days to assess droplet growth behavior over time. The findings revealed progressive droplet growth with increasing temperature while maintaining a relatively narrow size distribution. Kinetic analysis further indicated apparent first-order droplet growth behavior, with the apparent rate constant increasing from 0.0012 to 0.0032 day-1 as the temperature increased from 10 to 40 °C, corresponding to an activation energy of 22.51 kJ mol-1. These results provide mechanistic insight into the temperature-dependent kinetic stability of CLEO nanoemulsions, contributing to an improved predictive understanding of nanoemulsion stability in low-energy systems.