Effect of plasma activated mist (PAM) on inactivation of Listeria innocua and Klebsiella michiganensis on selected surfaces
Creators: name: Tumuluri, Tejaswini
Publisher: name: No Publisher Supplied
Year: 2024

description: Current fresh produce surface treatment methods for food safety include spraying or washing the produce with chemical sanitizers like chlorine, which may not be environmentally friendly. Cold plasma generated by Dielectric Barrier Discharge (DBD) and Plasma-Activated Mist (PAM) have shown the potential as alternatives to these sanitizing treatments. PAM is a mist of micron-sized water droplets that have been exposed to DBD plasma. DBD generates ozone and other excited nitrogen species with antimicrobial properties. PAM contains highly reactive oxygen and nitrogen species (RONS), which act as oxidizing agents and contribute to its antimicrobial properties. The objectives of this study were (1) to enumerate the microbial inactivation caused by DBD and PAM on TSA and glass slides and (2) to determine the efficacy of PAM on grape tomato, lime, and spiny gourd which have different surface topology.TSA plates separately inoculated with Listeria innocua and Klebsiella michiganensis were exposed to atmospheric pressure DBD plasma from 5 min to 20 min. Listeria innocua is a surrogate of pathogen Listeria monocytogenes and Klebsiella michiganensis is a surrogate of pathogen Salmonella. Bacterial reduction by DBD ranged from 3.4 to 4.8 log CFU/plate for Listeria innocua and from 2.1 to 4.5 log CFU/plate for Klebsiella michiganensis. For glass sides (surface roughness Pq = 0.28 ± 0.02 μm) which were spot inoculated similarly, the resulting log reductions were 2.9 to 4.2 log CFU/slide for Listeria innocua and 3.6 to 5.0 log CFU/slide for Klebsiella michiganensis. Higher values correspond to longer exposure times.Experiments were conducted on TSA and glass slides which spot inoculated separately by Listeria innocua and Klebsiella michiganensis and exposed to PAM from 5 min to 20 min. TSA plates showed reduction of 2.4 to 5.1 log CFU/plate for Listeria innocua and 2.5 to 4.0 log CFU/plate for Klebsiella michiganensis, depending upon the exposure time. For the glass slides reduction was 1.1 to 3.2 log CFU/slide for Listeria innocua and 3.4 to 4.8 log CFU/slide for Klebsiella michiganensis. In the experiments involving fresh produce, grape tomato (surface roughness Pq = 5.17 μm ± 0.53 μm), lime (Pq = 18.76 μm ± 3.00 μm) and spiny gourd (Pq = 101.50 μm ± 10.95 μm) were spot inoculated with known concentrations separately by Listeria innocua and Klebsiella michiganensis and treated in PAM for 5 min to 20 min. Bacterial reduction for Listeria innocua on the grape tomato was 2.7 to 3.4 log CFU/surface, on lime it was 2.3 to 2.7 log CFU/surface and for spiny gourd it was 0.7 to 1.0 log CFU/surface. The corresponding reductions for Klebsiella michiganensis were: 2.6 to 4.6 log CFU/surface for grape tomato, 2.2 to 3.7 log CFU/surface for lime, and 0.99 to 1.8 log CFU/surface for spiny gourd. Thus, both DBD and PAM have antibacterial potential in surface applications. However, between DBD and PAM, PAM is preferred since DBD produces ozone, which may not be environmentally friendly. Further studies can focus on scaling up of PAM for industrial applications.