Effect of high voltage atmospheric cold plasma on inactivation of Listeria innocua on Queso Fresco cheese, cheese model and tryptic soy agar

High voltage atmospheric cold plasma (HVACP) is a novel technology which has shown promising results on microbial inactivation under low temperature, and thus offers opportunities on decontamination of biological materials. In this study, Listeria innocua spot inoculated tryptic soy agar (TSA), Queso Fresco cheese (QFC) and cheese model (CM) samples were treated with HVACP under direct and indirect mode of exposure in dry air gas environment for 5 min. After direct HVACP treatment, a reduction of 5.0, 3.5 and 1.6 log(10) CFU/g was observed for TSA, CM and QFC, respectively. Direct plasma treatment was more effective in Listeria innocua inactivation on CM and QFC compared to indirect treatment. Surface analysis has shown that the differences in surface roughness and micro-structure of the substrate hugely impact the efficacy of the HVACP treatment by affecting the attachment of the bacteria cells on the surface and providing protective locations for the microbes within the surface.