Optimization of orange oil nanoemulsion formation by isothermal low-energy methods: influence of the oil phase, surfactant, and temperature.

Nanoemulsions are particularly suitable as a platform in the development of delivery systems for lipophilic functional agents. This study shows that transparent orange oil nanoemulsions can be fabricated using an isothermal low-energy method (spontaneous emulsification), which offers the advantage of fabricating flavor oil delivery systems using rapid and simple processing operations. Orange oil nanoemulsions were formed spontaneously by titration of a mixture of orange oil, carrier oil [medium-chain triglyceride (MCT)], and non-ionic surfactant (Tween) into an aqueous solution (5 mM citrate buffer at pH 3.5) with continuous stirring. The oil/emulsion ratio content was kept constant (10 wt %), while the surfactant/emulsion ratio (SER) was varied (2.5-20 wt %). Oil-phase composition (orange oil/MCT ratio), SER, and surfactant type all had an appreciable effect on nanoemulsion formation and stability. Transparent nanoemulsions could be formed under certain conditions: 20% surfactant (Tween 40, 60, or 80) and 10% oil phase (4-6% orange oil + 6-4% MCT). Surfactant type and oil-phase composition also affected the thermal stability of the nanoemulsions. Most of the nanoemulsions broke down after thermal cycling (from 20 to 90 °C and back to 20 °C); however, one system remained transparent after thermal cycling: 20% Tween 80, 5% orange oil, and 5% MCT. The mean droplet size of these nanoemulsions increased over time, but the droplet growth rate was reduced appreciably after dilution. These results have important implications for the design and utilization of nanoemulsions as delivery systems in the food and other industries.