Antimicrobial activity of low-pressure plasma treatment against selected foodborne bacteria and meat microbiota

The effects of helium and argon plasma treatments on inactivation of both pure bacterial cultures inoculated onto the surface of agarized media and the surface microbiota of meat were investigated. Cold plasmas were generated by high voltage discharge at low pressure (20 kPa) for 2, 5, and 10 min. The number of viable microorganisms was determined using a plate count method. Morphological changes were observed using scanning electron microscopy (SEM). Microbial log reduction depended on time of exposure and type of gas used. After a 10-min treatment with helium plasma, the total number of microorganisms, yeasts and molds, and psychrotrophic microorganisms was reduced in the range of 1.14-1.48 log cycles for pork and 0.98-2.09 log cycles for beef. A significant reduction of 2.00 log for Bacillus subtilis and Yersinia enterocolitica was achieved within 2 min of helium plasma treatment. Similar results were obtained for Staphylococcus aureus, Escherichia coli and Pseudomonas fluorescens after 5 min and 10 min of exposure. SEM revealed disruption and lysis of E. coli cells treated with helium plasma for 10 min, suggesting a bactericidal effect.