Antimicrobial activity of nanoemulsions of cinnamon, rosemary, and oregano essential oils on fresh celery

Nanoemulsions formulated with essential oils (EOs) can be applied to bacteria found on fresh food, however, scarce information is still available. This study aimed to evaluate the antimicrobial activities of EOs of cinnamon (CEO), rosemary (REO), and oregano (OEO) EOs encapsulated in oil-in-water nanoemulsions prepared using high-frequency ultrasound and applied onto fresh celery inoculated with Escherichia coli and Listeria monocytogenes. The characteristics of CEO, REO, and OEO nanoemulsions were: pH, 4.69–5.84; viscosity, 1.844–1993 mPa s; density, 1.004–1.018 g/cm3; color parameters, Lh > 80 (ah: negative and bh: positive); particle size (D50) 226–546 nm; phase separation, <10%; and encapsulation efficiency, >80%. Compared with the nonencapsulated EOs, EOs nanoemulsions were more effective against bacteria, requiring less than 50% of the EOs to reduce 5-log bacterial population. OEO nanoemulsions proved to be the most effective in inhibiting the evaluated bacteria. E. coli and L. monocytogenes were inhibited within <60 min with 5-log reduction. The Weibull model was used to describe the kinetics of bacterial inhibition on celery immersed in nanoemulsions. The predicted curves adequately fit the experimental data (R2 > 0.96), presenting low mean square error values (<0.35). EOs nanoemulsions demonstrated to be a good alternative to traditional synthetic antimicrobials for controlling both bacteria in fresh vegetables.