Inactivation of Salmonella typhimurium and Lactobacillus plantarum by UV-C light in flour powder

• Treatment with UV-C light resulted in an adequate system for the bacterial decontamination of flour.
• A new UV-C process has been developed for microbial inactivation in continuous flow of powder products.
• Four-second exposures of UV-C inactivated 4-log10 cycles of L. plantarum in flour.
• UV-C light inactivated 4-log10 cycles of Salmonella Typhimurium in flour.

This research evaluates the potential use of ultraviolet C light (UV-C) as a decontamination method for powdered foods, particularly of refined flour. This technology's lethal effectiveness was evaluated on Salmonella enterica subsp. Enterica serotype Typhimurium and Lactobacillus plantarum in wheat flour, and in laboratory liquid media of different aw and turbidities to evaluate the action mechanisms of UV-C light in powdered products. Initial results showed a large variability of lethality in flour, obtaining between 0.2 and 3.0 log10 cycles of inactivation. Results obtained in laboratory media and SEM analysis of contaminated flour indicated that the variability was due to a shadow effect on the efficacy of UV-C light and not due to the low water aw of the flour or starch content. Based on these conclusions, a 2-m vertical tunnel with twelve 480 W UV-C lamps was designed to treat flour by forming a continuous cloud of dust (0.05–2.4 kg/h). Inactivation levels of 4.0 to 1.7 log10 cycles of the population of L. plantarum in flour were achieved at flow rates of 0.2 and 2.4 kg/h respectively, with a maximum residence time of 4 s.Industrial relevanceThis investigation demonstrated the lethal efficacy of the application of UV–C light to inactivate microorganisms, both pathogenic and spoilage, present in flour. 4-log10 cycles of inactivation of both Salmonella Typhimurium and Lactobacillus plantarum were inactivated with UV-C treatments. A UV-C facility was built up which enabled to treat flour in continuous conditions creating a cloud of dust with treatments of 4 s and lethalities of 4-log10 reductions.