Influence of 405 nm light-emitting diode illumination on the inactivation of Listeria monocytogenes and Salmonella spp. on ready-to-eat fresh salmon surface at chilling storage for 8 h and their susceptibility to simulated gastric fluid

The aim of this study was to evaluate the antibacterial effect of 405 nm light-emitting diode (LED) against Listeria monocytogenes and Salmonella spp. on the surface of ready-to-eat (RTE) fresh salmon, and to determine the susceptibility of LED-illuminated bacterial cells to simulated gastric fluid (SGF). A cocktail culture of L. monocytogenes or Salmonella spp. was inoculated onto the freshly cut salmon surface and then illuminated by 405 nm LED (16 ± 2 mW/cm2) for 8 h at 4 and 12 °C. Illuminated cells were subsequently exposed to SGF at 37 °C. Results showed that the populations of LED-illuminated L. monocytogenes and Salmonella cells were significantly (P < .05) reduced by 0.4 and 0.5 log CFU/cm2 for 8 h compared to non-illuminated cells at 4 °C. At 12 °C, significant reductions of 0.3 and 0.4 log CFU/cm2 were observed for LED-illuminated cells, respectively. The D-values of LED-illuminated L. monocytogenes cells at 4 and 12 °C in SGF were 6.0 and 9.4 min, which were significantly lower than those of non-illuminated cells (14.4 and 15.6 min), respectively. Similarly, LED illumination also caused significant decreases in the D-values of Salmonella cells, resulting in 19.7 and 32.9 s of LED-illuminated cells at 4 and 12 °C, respectively, compared to those of non-illuminated cells (37.5 and 46.7 s). No significant color change was observed for LED-illuminated salmon for 8 h at both 4 and 12 °C. Although 405 nm LED illumination did not largely reduce the population of L. monocytogenes and Salmonella cells on fresh salmon during storage at chilling temperatures, these results indicate that 405 nm LED illumination might make them sensitive to gastric acid. Thus, this study suggests that the implementation of 405 nm LED in the storage of RTE fresh salmon products could be useful to minimize the risk of listeriosis and salmonellosis.