Synergistic effects of ultrasound combined with aqueous chlorine dioxide on the reduction of Yersinia enterocolitica in leaf mustard ( Brassica juncea )

Recent disease outbreaks linked to leafy vegetable crops have highlighted Yersinia enterocolitica as a significant foodborne pathogen. Because this pathogen can enter the horticultural supply chain through various stages, it is difficult to completely eliminate. This study aims to assess the synergistic effects of ultrasound (US) treatment (25 kHz, 200 W for 10–60 min), used in combination with chlorine dioxide (ClO₂) (10, 30, 50, 70, and 100 ppm of Cl₂), on the reduction of Y. enterocolitica (7.44 ± 0.18 log CFU/g) in leaf mustard. After 30 min of US treatment, a reduction of over 1 log CFU/g was noted, with a maximum decrease of 1.89 log at 60 min. Chlorine dioxide alone achieved a reduction of 1.19 log CFU/g at 100 ppm. Separately, these two types of treatment resulted in reductions of 0.39–1.89 (with US) and 0.16–1.19 (with ClO₂) log CFU/g, respectively. Treatment by using US and ClO₂ in combination was the most effective in reducing the Y. enterocolitica counts on leaf mustard, resulting in log reductions of ≥5.0 log CFU/g. Microbial counts of 1.14, 1.35 and 2.28 log CFU/g against Y. enterocolitica in leaf mustard were obtained by using the synergistic combinations of 50 min US/100 ppm ClO₂, 60 min US/70 ppm ClO₂, and 60 min US/100 ppm ClO₂, respectively. Quality assessments showed no significant differences in the Brix content (4.8–5.1 °Brix), or hardness (1504.7–1634.0 g/cm²) compared to the controls (p > 0.05). Therefore, these results suggest that the combination of US and ClO₂ can potentially be used in the kimchi industry to effectively inactivate Y. enterocolitica without causing the quality of leaf mustard to deteriorate.