Effect of surface roughness on the efficacy of Plasma Activated Mist (PAM) for inactivation of Listeria innocua and Klebsiella michiganensis

Abstract

Cold plasma generated by dielectric barrier discharge (DBD) and DBD combined with nebulized liquid microdroplets to generate plasma-activated mist (PAM) have shown the potential as a surface decontamination method for the food industry. The objective of this research was to measure the microbial inactivation caused by DBD and by PAM on tryptic soy agar (TSA) and on glass slides and to determine the efficacy of PAM on selected surfaces having different surface topographies. Tryptic soy agar in Petri dishes and on glass slides (surface roughness Pq = 0.28 ± 0.02 μm) was inoculated with either 0.1 mL of inoculum containing Listeria innocua (8.4 ± 0.1 log CFU/mL) or Klebsiella michiganensis (8.8 ± 0.2 log CFU/mL) and exposed to either DBD or PAM for 5 to 20 min. Glass slides, grape tomatoes (Pq = 5.17 μm ± 0.53 μm), limes (Pq = 18.76 μm ± 3.00 μm), and spiny gourds (Pq = 101.50 μm ± 10.95 μm) were also surface-inoculated with L. innocua or K. michiganensis and exposed to PAM for 5 to 20 min. No significant difference in microbial inactivation was observed between DBD plasma and PAM for all treatment times. The smoothest surface (glass) showed the highest reduction in L. innocua (3.4 ± 0.2 log CFU/item) and K. michiganensis (5.7 ± 0.0 log CFU/item) after PAM treatment. The roughest surface (spiny gourd) yielded a significantly lower reduction for L. innocua (1.0 ± 0.2 log CFU/item) and K. michiganensis (1.8 ± 0.1 log CFU/item). L. innocua was less susceptible to inactivation by PAM compared K. michiganensis. This study highlighted the importance of surface roughness on microbial inactivation of L. innocua and K. michiganensis by DBD and PAM on produce surfaces.