Changes in characteristics of nanoemulsion of cinnamon oil and their relationships with instability mechanisms during storage

Development of nano-structured food delivery systems containing essential oils are finding growing interest due to their unique physicochemical and potential functional properties such as high stability, optical transparency, and improved bioactivity. Cinnamon oil of bark of Cinnamomum burmannii was formulated into nanoemulsion systems and their characteristics during storage were evaluated to obtain their relationships with possible destabilization mechanisms. Nanoemulsion was prepared using a phase inversion technique incorporating cinnamon oil (5% and 10%) and non-ionic emulsifier (75% of the oil). The emulsions were kept at 20, 30, 40 degrees C and their physical characteristics were analyzed over time during 8 weeks storage. Average droplet sizes of 192.6 and 184.3 nm were produced at the beginning of storage and they tended to increase during storage. Droplet sizes and polydispersity index exhibited the same increase trends, while the absolute value of zeta potential and viscosity showed decrease trends in general. Creaming appeared to dominate the destabilization of nanoemulsion accompanied by Ostwald ripening and followed by oil sedimentation. Practical applications Consumers become more aware of the uses of natural ingredients in food formulation in-line with the increase trends in back-to-nature lifestyle. Cinnamon oil has been used for food flavoring and preservation but its incorporation into aqueous-based formulation is still difficult due to its hydrophobicity. Development of nanoemulsion is a prospective approach to the dispersity problem. This study provides valuable information in formulating nanoemulsion suitable for the food delivery system. Identification of changes in nanoemulsion characteristics during storage gives the feature of coarsening behavior useful in designing approaches to control their instability.