Preparation of nanoemulsions from Elsholtzia kachinensis and Elsholtzia ciliata essential oils via ultrasonic homogenization and their antibacterial and anticancer activities†

Plant essential oils can function as effective antibacterial and anticancer agents, but their low solubility and hydrophobic nature limit their practical applications. In this study, we report the preparation of nanoemulsions of Elsholtzia kachinensis and Elsholtzia ciliata via ultrasonic homogenization and the characterization of their antibacterial and anticancer activities for the first time. The product characteristics were evaluated based on turbidity, droplet size, polydispersion index, zeta potential and electrophoretic mobility. The activities were evaluated based on their ability to inhibit the growth of bacteria and HepG2 cancer cells. The Elsholtzia kachinensis and Elsholtzia ciliata nanoemulsions exhibited good stabilities, narrow size distributions with droplet sizes of 72.81 nm and 32.13 and zeta potentials of −27.8 mV and −11.2 mV, respectively. The Mulliken atomic charge analysis demonstrated that the E. kachinensis nanoemulsion had greater stability than the E. ciliata nanoemulsion. In vitro anti-bacterial studies using strains of Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumoniae, Staphylococcus aureus, Bacillus subtilis and Staphylococcus epidermidis showed that both nanoemulsions exhibited higher growth inhibition efficiency than the respective essential oils. The inhibition efficiency of the Elsholtzia ciliata nanoemulsion against Bacillus subtilis and Staphylococcus epidermidis was 5 times higher than those of the corresponding essential oils. The HepG2 cell inhibition efficiency was about 80% for both nanoemulsions at a concentration of 500 μg mL⁻¹, while the commercial essential oils inhibited only about 60% of HepG2 cells. Therefore, Elsholtzia kachinensis and Elsholtzia ciliata nanoemulsions can be potential candidates for modern biopharmaceuticals in the future.