Estimation of antimicrobial effect of non-thermal microwave plasma jet in model experiment

Abstract

Relevance. The plasma treatment of ready-to-eat foods the potential use to increase a storage time and a food safety. On the first step seems important to evaluate the bactericidal effect of a non-thermal (non-equilibrium) plasma on a natural association bacteria isolated from the food.Methods. The non-thermal plasma source based on an argon plasma jet in a microwave (streamer) discharge at atmospheric pressure was used. Lactobacillus culture isolated from a walnut in the natural association and the vegetative form was treated. Sowing was carried on Petri dishes with Endoʼs agar. The exposure time is 60 s, 180 s and 360 s. The distance from the plasma jet source’s nozzle to the Endoʼs agar surface was 30 mm. The diameter of the growth inhibition zone of Lactobacillus on the dense nutrient medium was determined.Results. The round transparent Endo’s agar area — the zone of growth inactivation of colony-forming units in bacterial lawn of Lactobacillus after exposure to argon plasma jet was registered. After counting colony-forming units, a decrease in the number of Lactobacillus colonies grown after a 360-second exposure was found. At a 60-second exposure, no significant decrease in the number of grown colony-forming units was observed. The bactericidal effect is noticeable after a 180-second exposure to the plasma jet. With an increase in the exposure time to 360 s, the sterilization area on the surface of the agar in the Petri dish increased. The maximum diameter of the Lactobacillus growth inactivation zone did not exceed the diameter of the nozzle of the plasma jet source (36 mm). Under the influence of plasma, the color of the Endo agar changed in the zone of direct exposure to the plasma jet.