Inactivation of Listeria monocytogenes, Escherichia coli O157:H7, and Staphylococcus aureus by sequential light-emitting diodes (LEDs) treatment at 365 nm and 420 nm

Frequent outbreaks caused by foodborne pathogens pose long-term risks to consumer health. To proactively reduce the load of pathogenic bacteria during food processing, a novel light-based antibacterial approach was developed by sequential application of 365 nm and 420 nm light-emitting diodes (LEDs). Results demonstrated that after treatment with 365 nm (480 J/cm(2)) followed by 420 nm (307.2 J/cm(2)), the reduction of Listeria monocytogenes reached 4.05 +/- 0.31 log CFU/mL, significantly higher (an additional 1.8 log CFU/mL, P < 0.05) than cumulative reductions achieved by each 365 nm (2.25 +/- 0.92 log CFU/mL) and 420 nm (0.02 +/- 0.15 log CFU/mL) treatments. Further analysis revealed that the enhancement in bacterial reduction achieved through the sequential treatment with 365 nm and 420 nm was primarily driven by the exposure time to 365 nm. The inactivation mechanisms were investigated, considering possible photothermal, physical, and oxidative effects. Findings showed that the antibacterial effect of sequential treatment was mainly ascribed to intracellular oxidation generated by reactive oxidative species (ROS), namely hydrogen peroxide and superoxide anion. The antibacterial mechanism of two LEDs may result from the sensitization of bacterial cells to excessive ROS, as evidenced by fluorescent intensity measurements and chemical scavenger assays. This research provides new insight for improving the efficacy of UVA and blue light treatment to control food contamination by Listeria.