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Formulation, characterization and antimicrobial effect of cinnamon oil nanoemulsions

Yıldırım, Simge Tutku
Activities of essential oils, such as antimicrobial, antioxidant and anticancer have been recognized for decades. To utilize the functionality of these materials in foods as natural additives instead of synthetic active materials, oil-in-water (O/W) nanoemulsions that are obtained by low and high-energy methods have been intensively explored in recent years. The purpose of this study was to formulate stable cinnamon oil nanoemulsions (NEs) having higher antimicrobial activity by using the low-energy approach: spontaneous emulsification (SE) method. To prepare the nanoemulsions, oil phase containing cinnamon oil (CO) and the carrier oil (coconut oil (CNO)) at various concentrations and surfactant (Tween 80) was titrated into an aqueous phase (distilled water) that was being stirred continuously. 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) techniques. Both DLS and TEM gave parallel results and mean particle size of the most stable NEs were found as ~100 nm for 6:4 (CO: CNO) oil phase composition. Effect of SE on antimicrobial activity was compared with cinnamon oil solutions that included same concentrations of CO and results showed that antimicrobial activity increased 10-25% on the NEs prepared by spontaneous emulsification. NEs were also prepared by using two high energy homogenization methods: microfluidization and ultrasonication. When spontaneous emulsification, microfluidization and ultrasonication were compared at same CO%, at higher CO concentrations (6%, 8% and 10%), results were not significantly different for particle sizes. Moreover, for all CO concentrations, antimicrobial activity could not be enhanced by microfluidization towards E. coli. However, at higher CO concentrations (8% and 10%), enhanced antimicrobial activity were obtained by spontaneous emulsification and ultrasonication methods, and these results were not found to be significantly different (p>0.05). This study revealed that CNO could successfully be utilized as a carrier oil for preparing nanoemulsions and stable cinnamon oil nanoemulsions could be prepared at lower surfactant concentrations by the spontaneous emulsification method.