The inactivation of Shigella flexneri by synergistic effect of ultrasound combined with basil essential oil nanoemulsion and application in cabbage cleaning

Shigella flexneri has caused significant health threats due to its widespread contamination. In this study, basil essential oil nanoemulsion (BEON) with good physical stability was produced by emulsification technique of high-power ultrasound (US). The antibacterial effect of US combined with BEON against S. flexneri in phosphate-buffered saline (PBS) and cabbage leaves was investigated. The results showed that US (20 kHz, 207 W/cm(2)) combined with 0.4 mg/mL BEON generated >3.66 log CFU/mL reductions of S. flexneri in PBS, which were greater than the sum of single US and BEON treatments. US+BEON exacerbated oxidative stress, resulting in increase of intracellular reactive oxygen species and malondialdehyde. Confocal laser scanning microscopy, flow cytometry, protein and nucleic acid release assays showed that the US+BEON revealed damage to cell membrane integrity. Field emission scanning electron microscopy-based morphological measurements show that US+BEON changed caused serious damage to cell morphology of S. flexneri. During storage at 4 degrees C for 12 day, US+BEON treatment significantly reduced the number of S. flexneri in cabbage leaves (P<0.05), in comparison with the individual treatments. Moreover, the treatments showed no negative effect on the quality of fresh-cut cabbages during storage and presented positive sensory evaluation. These findings suggest that US+BEON is a promising technique for bacterial inactivation and has the potential to be used for cleaning fresh-cut produce to provide their microbial safety.