Inactivation of Escherichia coli O157:H7 and Listeria monocytogenes inoculated on raw salmon fillets by pulsed UV-light treatment

The efficacy of pulsed UV-light to inactivate of Escherichia coli O157:H7 and Listeria monocytogenes Scott A on salmon fillets was investigated in this study by evaluating the effects of treatment times and distance from the UV strobe. The sterilization system generated 5.6 J cm^-2 per pulse at the lamp surface for an input voltage of 3800 V and three pulses per second. Skin or muscle side inoculated salmon fillet (8 cm × 1.5 cm) in a Petri dish was placed on shelf at three different distances from the UV strobe; 3, 5, and 8 cm. At each distance, the pulsed UV-light treatment was performed for 15, 30, 45, and 60 s. For E. coli O157:H7, maximum log₁₀ reduction was 1.09 log₁₀ CFU g^-1 on muscle side at 8 cm for 60-s treatment, whereas 0.86 log₁₀ CFU g^-1 reduction on skin at 5 cm for 30-s treatment. For L. monocytogenes Scott A, maximum reduction was 1.02 log₁₀ CFU g^-1 at 8 cm for 60-s treatment on skin side, whereas 0.74 log₁₀ CFU g^-1 reduction on muscle at 8 cm for 60-s treatment. The fillet's surface temperature increased up to 100degrC within 60-s treatment time. Therefore, some fish samples were overheated after 30 and 45 s at 3- and 5-cm distances from light source, respectively, which resulted in visual colour and quality changes. Overall, this study demonstrated that about one log reduction (c. 90%) of E. coli O157:H7 or L. monocytogenes could be achieved at 60-s treatment at 8 cm distance without affecting the quality.