Synergistic bactericidal effect of ultrasound combined with oregano essential oil nanoemulsion on Listeria monocytogenes and its application in blueberry preservation

Fruits and vegetables are susceptible to Listeria monocytogenes. In this study, the nano emulsion of oregano essential oil (OEO) prepared by ultrasonic (US) nanoemulsion method combined with US has a promising synergistic bactericidal effect on L. monocytogenes, with 255 W/cm2+0.06 μL/mL origano essential oil nanoemulsion (OEONE) completely kill the initial number of bacteria (8.67 ± 0.17 log CFU/mL) after 15 min of treatment. Compared to control, reactive oxygen species (ROS), malondialdehyde (MDA) detection, nucleic acid and protein release tests showed that US + OEONE intensified cell membrane lipid peroxidation and increased cell membrane permeability. Flow cytometry (FCM) once again demonstrated the damage to cell membrane integrity caused by US + OEONE treatment. The results of field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) indicate that US + OEONE treatment alter cell morphology. Also, this study provides evidence to support the use of US+OEONE as a practical preservation method to minimize the presence of L. monocytogenes on the surface of blueberries, and sensory evaluations indicate that US+OEONE-treated blueberries are acceptable. In addition, this method demonstrated the ability to retard microbial proliferation without affecting the color, texture, and antioxidant properties of blueberries during storage. These results indicate that the implementation of US+OEONE is expected to improve the microbial safety of fresh produce.