Antibacterial mechanism of riboflavin-mediated 460 nm light emitting diode illumination against Listeria monocytogenes in phosphate-buffered saline and on smoked salmon

Abstract

The aim of this study was to elucidate the antibacterial mechanism of riboflavin-mediated 460 nm light emitting diode (LED) illumination against Listeria monocytogenes in phosphate buffered saline (PBS) solution and on the surface of smoked salmon by determining reactive oxygen species (ROS) production, bacterial membrane permeability, and DNA damage in PBS as well as bacterial metabolic inhibition on smoked salmon. Its antibacterial efficacy against L. monocytogenes in PBS and on the surface of smoke salmon was also evaluated. The results showed that LED illumination alone reduced 0.6 log CFU/ml of L. monocytogenes at dose of 0.2 kJ/cm2, while illumination with riboflavin (100 μM) inactivated 5.6 log CFU/ml in PBS at 20 °C. On the surface of smoked salmon, LED illumination with/without riboflavin reduced less than 1.0 log CFU/cm2 of L. monocytogenes populations at 4 °C at 12.8 kJ/cm2. At 10 °C, bacterial populations on non-illuminated and illuminated samples increased to 5.9 and 4.4 log CFU/cm2, respectively, whereas riboflavin-mediated LED illumination inactivated 1.0 log CFU/cm2. The amount of ROS observed in illuminated cells with riboflavin was higher than those of non-illuminated and illuminated cells. LED illumination alone induced cellular damage to metabolism of RNA and protein, while riboflavin-mediated illumination caused additional metabolic inhibition to DNA. Therefore, these results suggest that the antibacterial mechanism of riboflavin-mediated 460 nm LED illumination might be due to membrane and DNA damages by ROS generated from photo-reaction of riboflavin as well as metabolic inhibition. This study could provide novel insight in the application of riboflavin-mediated 460 nm LED technology to preserve smoked salmon at refrigeration temperatures, minimizing the risk of listeriosis.