Formulation optimization and characterization of carvacrol-loaded nanoemulsions: In vitro antibacterial activity/mechanism and safety evaluation

Practical application of carvacrol in different fields including foods and biopesticides is limited because of its instability and water insolubility. To overcome these problems, carvacrol can be loaded into nanoemulsions. In this study, carvacrol-loaded nanoemulsions (CNs) were formulated and characterized, and the most suitable emulsifier was selected. The optimized formula of CNs by Box-Behnken design was: carvacrol 5%, emulsifier (Tween-80) at 8% and the shearing time of 7 min. The antibacterial activity of this optimum formulation of CNs was evaluated by the measurement of inhibition zone diameter, minimum inhibitory concentration, and minimum bactericidal concentration. The antibacterial mechanism of CNs was also studied by scanning electron microscopy, reactive oxygen species, malondialdehyde, and intracellular lysate leakage. CNs damaged the structure of bacterial cells and the permeability of bacterial cell membrane, resulting in the leakage of cellular contents from bacteria. Also, at the same concentration, CNs had a higher cell survival rate and less apoptosis compared with commercial carvacrol aqueous solution; therefore, CNs had a higher biological safety. The final formulation solved the volatility and instability of carvacrol during use, along with providing a new technology for preparing CNs with a long-term stability and good antibacterial activity. • The formula composition of carvacrol nanoemulsions was optimized by Box-Behnken design. • Carvacrol nanoemulsions had strong antibacterial activity against S. aureus and E. coli . • The antibacterial mechanism of carvacrol nanoemulsion was studied by SEM, ROS, and MDA. • Carvacrol nanoemulsions had less effect on L-02 cells.