Decontamination of hard cheeses by pulsed UV-light

Cheese is a ready-to-eat food, which may be contaminated on the surface by undesirable spoilage and pathogenic microorganisms at the production, packaging, and post-packaging processes. Penicillium roqueforti is commonly found on cheese surfaces at refrigerator temperatures, and is one of the most common spoilage fungal species. Listeria monocytogenes has been associated with food-borne listeriosis by consumption of cheese. Therefore, there is a need for decontamination of cheese at post-processing stages. Pulsed UV-light is a non-thermal method for food preservation that involves the use of intense, short duration pulses to ensure microbial decontamination on the surface of either foods or packaging materials. In this study, efficacy of pulsed UV- light to inactivate artificially inoculated P. roqueforti and L. monocytogenes on packaged and unpackaged hard cheeses were investigated. Treatment times and the distance from the UV strobe were evaluated to determine optimum treatment conditions. Packaged and unpackaged cheeses were treated at 5, 8, and 13-cm distances up to 60s. For P. roqueforti, maximum log reduction was 1.32 log 10 CFU/cm2 at 40-s and 5-cm distance on unpackaged cheese and 1.24 log 10 CFU/cm2 on packaged cheese at the same treatment conditions. Log reductions of L. monocytogenes at the same treatment conditions were about 2.9 and 2.8 CFU/cm2 packaged and unpackaged cheeses, respectively. The temperature changes and total energy increased directly proportional with treatment time and inversely with distance between UV lamp and samples. The changes in color and lipid oxidation extent were determined at mild (5-s at 13-cm), moderate (30-s at 8-cm), and extreme (40-s at 5-cm) treatments. The color and chemical quality of cheeses did not show significant difference after mild treatments (p>0.05). The plastic packaging material (polypropylene) was evaluated in terms of mechanical properties after mild, moderate, and extreme treatments, as well. There was a decreasing trend for elastic modulus. However there was no significant difference between untreated, mild, and moderate treatments (p>0.05). Overall, these results demonstrated that pulsed UV- light has potential to inactivate P. roqueforti and L. monocytogenes on the surface of hard cheeses.