Development and characterization of promising o/w nanoemulsions containing sweet fennel essential oil and non-ionic sufactants

• Phase behavior studies provided macroscopically different formulations.
• Nanoemulsions were prepared by a high-energy method in a high pressure homogenizer.
• Effect of surfactant/oil ratio on mean droplet size and distribution was studied.
• Nanoemulsions droplet size increased over time due to Ostwald ripening and coalescence.
• Formulations 4.6 and 5.5, 2.8* and 3.7* showed constant droplet size during at least 3 months.

Nanoemulsions have attracted much attention due to their application in material science, food, nutraceutical and pharmaceutical field as delivery systems for lipophilic bioactive ingredients, such as essentials oils. The aim of this study is to develop and characterize oil-in-water (o/w) nanoemulsion-based delivery systems for vehiculation of sweet fennel oil. To this purpose, a pseudo-ternary phase diagram (PTD) was constructed based on sweet fennel as oily phase, surfactant mixture and water through the water titration method. The influence of surfactant concentration was investigated by varying the oil/surfactant ratio (OSR). After constructing PTD, nine selected formulations were processed in a high-pressure homogenizer (HPH). Results suggested nanoemulsions presented mean droplet sizes values smaller than 100 nm, and size distributions and polydispersity index (PdI) maximum of 0.3 when prepared under the conditions employed in this work. Given the non-ionic feature of the surfactants employed here, the formulations tested presented low negative charges (around −3 mV). Shear viscosity measurements were performed and a newtonian rheological behavior was observed for all formulations. Sweet fennel oil showed an antioxidant potential, with an EC50 value 111 μg/mL. The results obtained might corroborate to the application of sweet fennel oil nanoemulsions as potential candidate for antioxidant topical formulations.

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