Peppermint and Myrtle nanoemulsions: Formulation, stability, and antimicrobial activity

Abstract

Myrtle and Peppermint oil (Myrtus communis and Mentha pulegium) nanoemulsions were formulated using non-ionic surfactant Tween 80 and water through a two-step homogenization process (high-speed homogenizer then high-pressure homogenizer). Physicochemical parameters particularly droplet average diameter, microscopic and macroscopic aspects, pH, viscosity, density, turbidity, refractive index, stability (thermal, physical, and osmotic stability), and antibacterial activity kinetic against E. coli and B. subtilis, have been measured. Obtained results indicate that the formulated nanoemulsions displayed an average droplet diameter inferior to 101 nm and comparable physicochemical characteristics. Considering their stability, Peppermint and Myrtle nanoemulsions exhibited suitable stability under pH, thermal (droplet size comprised between 80 and 1351 nm), and ionic stress as well as after 22 days of storage at 4 °C (average droplet diameter comprised between 90 and 188 nm). Concerning inhibition of bacterial growth, antibacterial activity against E. coli and B. subtilis revealed a marked efficacy particularly against E. coli (Peppermint nanoemulsions reached 99% of growth inhibition), and that efficiency was well kept even upon 22 days of storage at 4 °C. These results may establish the promising interest in Myrtle and peppermint essential oils for the food industry using nanoemulsion-based delivery systems.