Intense pulsed light (IPL) and UV-C treatments for inactivating Listeria monocytogenes on solid medium and seafoods

Abstract

The inactivation effects of intense pulsed light (IPL) on Listeria monocytogenes surface-inoculated on solid medium and on seafoods such as flatfish, salmon, and shrimp fillets were investigated for various light doses (0.11–1.75mJ/cm2 per pulse), number of pulses (0–9800 pulses, treatment time of 0–1960s), and total fluences (0–17.2J/cm2), and also the inactivation characteristics of UV-C irradiation on L. monocytogenes were evaluated for treatment time of 0–1960s. Besides, any structural damage to the treated cells after IPL and UV-C treatments was evaluated by transmission electron microscopy (TEM). On the solid medium, approximately 4.0- and 6.0-log reductions of L. monocytogenes cells were achieved with UV-C irradiation for 1000s and with IPL treatment for 180s (900 pulses) at a fluence of 1.75mJ/cm2 per pulse, respectively, with a negligible temperature rise (<2.0°C) during treatment. On the seafood products, IPL treatment at 1.75mJ/cm2 per pulse produced approximately 2.2-, 1.9-, and 1.7-log reductions of L. monocytogenes cells inoculated onto shrimp, salmon, and flatfish fillets, respectively, for 3600 pulses (720s, total fluence of 6.3J/cm2) and approximately 2.4-, 2.1-, and 1.9-log reductions, respectively, for 6900 pulses (1380s, total fluence of 12.1J/cm2), with a slight temperature rise (<5.0°C) and no observable effect on the food color. Meanwhile, UV-C treatment on the inoculated fish fillets did not show significant effect on irradiation time of 0–1960s. TEM observations clearly indicated destruction of the cell wall, cytoplasm shrinkage, and leakage of the cellular contents from the cytoplasm in IPL-treated L. monocytogenes cells, unlike UV-C treated cells.