High voltage atmospheric cold plasma inactivation of Listeria monocytogenes in fresh Queso Fresco cheese

Listeria (L.) monocytogenes is a significant pathogen found in ready-to-eat meat and dairy products. Soft cheeses, such as Queso Fresco cheese (QFC), are particularly sensitive to Listeria contamination, and occasionally serve as a source of food-borne illness outbreaks. In the present study, clinical and cheese isolates of L. monocytogenes were assayed for phenotypic characteristics following sub-lethal high voltage atmospheric cold plasma (HVACP) treatment. Reductions in biofilm formation, swimming motility, and growth dynamics were observed following HVACP treatment. Microbial enumeration of 1-, 10-, and 100-g fresh QFC following 0, 1, 2, or 3 min of HVACP demonstrated significant reductions in L. monocytogenes after 1 min (P-value <0.05), with increasing efficacy with prolonged exposure. A mass-dependent effect was observed between treatments of 1-, 10-, and 100-g QFC in regard to treatment efficacy. This result indicates that greater L. monocytogenes reduction on a larger QFC mass requires greater exposure of the L. monocytogenes to the reactive gas species. Optical absorption spectroscopy confirmed a reduction in reactive gas species for each log increase in QFC mass, however, an equivalent volume of inert foam resulted in increased reactive gas generation compared to QFC. In conclusion, we demonstrate both the application and limitations of HVACP treatments of QFC in the currently defined experimental parameters.