Cinnamon oil nanoemulsions by spontaneous emulsification: Formulation, characterization and antimicrobial activity

- Coconut oil was used as the carrier oil to formulate cinnamon oil nanoemulsions.
- Cinnamon oil: Coconut oil at ratio of 6:4 provided the most stable nanoemulsions.
- Antimicrobial activity of nanoemulsions were enhanced by spontaneous emulsification.

The goal of this study was to formulate stable cinnamon oil nanoemulsions (NEs) exhibiting high antimicrobial activity by using the low-energy approach: spontaneous emulsification (SE) and compare it with two high-energy methods. To prepare the nanoemulsions by SE, oil phase containing cinnamon oil (CO) and carrier oil (coconut oil (CNO)) at different ratios (2:8-10:0) and surfactant (Tween 80) at 10% (w/w) was titrated into an aqueous phase (distilled water). For antimicrobial activity, agar disc diffusion method with E. coli as the model microorganism was used. NEs were characterized by Dynamic Light Scattering (DLS) and Transmission Electron Microscopy (TEM). Both DLS and TEM gave parallel results and mean particle size were found as ∼ 100 nm for 6:4 (CO: CNO) oil phase composition. These NEs also showed high physical stability during one-month storage. NEs were also prepared by using two high-energy homogenization methods: microfluidization and ultrasonication. Ultrasonication and SE showed similar trends for mean particle size and microbial activity. Microfluidization resulted in the smallest mean particle size (p < 0.05) and antimicrobial activity was not effected from cinnamon oil concentration (p > 0.05).