Caprylic acid-mediated photodynamic inactivation of foodborne pathogens on sliced cheese using 356-nm UVA light

Abstract

This study evaluated the bactericidal efficacy of combined UVA irradiation and caprylic acid (CPA) against major foodborne pathogens in phosphate-buffered saline (PBS) and on sliced cheese and investigated its inactivation mechanism. In PBS, UVA alone caused negligible reductions after 20 min, whereas 0.15% CPA reduced E. coli O157:H7, S. Typhimurium, and L. monocytogenes by 0.96, 1.17, and 2.72 log CFU/mL, respectively. Combined UVA-CPA treatment further increased reductions to 1.56, 1.72, and 4.12 log CFU/mL, respectively. Because L. monocytogenes was the most susceptible, its cellular responses were further analyzed. Compared with the control and UVA alone, CPA and UVA-CPA significantly increased intracellular ROS generation and membrane damage, whereas UVA-CPA caused the greatest impairment of respiratory-chain dehydrogenase and efflux activities, indicating that enhanced inactivation was mainly associated with metabolic dysfunction and weakened cellular defense. On sliced cheese, UVA-CPA achieved reductions of 2.52, 3.11, and 3.58 log CFU/25 g for E. coli O157:H7, S. Typhimurium, and L. monocytogenes, respectively, with only minor quality changes (ΔE < 1.7 and no significant change in maximum cutting force). These findings suggest that UVA-CPA is a promising hurdle technology for improving the microbial safety of sliced cheese.