Synergistic mechanism and enhanced inactivation exhibited by UVA irradiation combined with citric acid against pathogenic bacteria on sliced cheese

The purpose of this study was to investigate the synergistic bactericidal effect and mechanism of the simultaneous treatment with ultraviolet-A irradiation (UVA) and citric acid (CA) against Escherichia coli O157:H7, Salmonella Typhimurium, and Listeria monocytogenes on sliced cheese. Simultaneous UVA and 0.5% CA treatment for 90 min resulted in 3.63-, 3.21-, and 5.17-log CFU/mL reductions in E. coli O157:H7, S. Typhimurium, and L. monocytogenes, respectively, which involved 1.42-, 1.66-, and 3.32-log CFU reductions, respectively that were attributable to the synergistic action of the combined treatments. Through mechanism analyses, damage to the cell membrane, production of intracellular reactive oxygen species (ROS), and inactivation of intracellular enzymes were identified as the main factors contributing to the synergistic lethal effect of UVA-CA combined treatment. Additionally, the UVA-CA treatment for 90 min did not affect the texture and color parameters. Overall, the findings of this study demonstrate the potential of the combined UVA-CA treatment in improvement of the microbial safety of dairy products. •Combined treatment of citric acid (CA) and UVA light was used to inactivate major pathogens on sliced cheese.•The highest synergistic effect was observed against Listeria monocytogenes.•The potential mechanisms underlying the synergistic bactericidal effect were elucidated.•Treatment with UVA-CA combination did not adversely affect the sliced cheese quality.