Non-Thermal Inactivation of Listeria monocytogenes in Dairy Products Using Pulsed Light Technology

Listeria monocytogenes is a significant food safety concern in ready-to-eat dairy products, and the demand for minimally processed products with extended shelf life has driven interest in non-thermal decontamination technologies. Pulsed light technology, which applies short, intense pulses of broad-spectrum white light, offers potential as a surface decontamination method. This study evaluates the efficacy of pulsed light treatment for inactivating Listeria monocytogenes on the surface of yoghurt containers and on sliced white cheese produced at a dairy plant in Kaduna, North West Nigeria. Inoculation studies were conducted at defined contamination levels of 10 to the 6 CFU per cm squared, and pulsed light treatments were applied at fluences of 0.5, 1.0, 2.0, 4.0, and 8.0 J per cm squared. Inactivation kinetics were fitted to the Weibull model. The effect of treatment on sensory quality including colour, aroma, and textural attributes of the cheese was also evaluated. Results showed a maximum inactivation of 3.8 log CFU per cm squared on yoghurt containers at 8.0 J per cm squared. On cheese surfaces, maximum inactivation was 2.4 log CFU per cm squared due to surface topography effects. No significant sensory quality changes were detected at fluences below 4.0 J per cm squared. Weibull model shape parameters indicated tailing behaviour, suggesting a resistant subpopulation requiring further investigation. The study contributes to non-thermal food safety technology literature with specific application to Nigerian dairy processing conditions. Keywords: pulsed light, Listeria monocytogenes, non-thermal processing, dairy, inactivation kinetics