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.

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Introduction. New methods of sterilization with non-thermal atmospheric pressure plasma remain an extremely relevant field of food science. The present research estimated the effect of non-thermal argon plasma on lactic acid bacteria obtained from walnuts. Study objects and method. The non-thermal argon plasma was generated by electrode discharge induced by a coaxial microwave plasmatron at atmospheric pressure. The discharge was generated in a special electrode construction. Its stability was achieved via low gas flow through the discharge gap. Argon consumption was 10 L/min. The study involved Lactobacillus plantarum and Lactobacillus mali in their natural association and vegetative form. Endo’s medium (Endo agar) was inoculated with lactobacilli. 100 μl of the suspension were added into a Petri dish with nutrient medium and carefully rubbed with a spreader. The plates with Endo agar inoculated with lactobacilli were placed under plasma radiation at a distance of 45 mm. The biocidal effect of plasma radiation was estimated by the diameter of the affected areas. After the plasma treatment, the Petri dishes were incubated in an incubator for 24–48 h at 37°C, after which the diameters of the affected areas were measured again. Results and discussion. The paper introduces experimental data on the effect of argon plasma on lactobacilli isolated from food. After treating the surface of inoculated Petri dishes with non-thermal plasma for five minutes, the diameter of the inhibition zone reached the diameter of a Petri dish (80 mm) and exceeded the diameter of the spark gap of the plasma generator (36 mm). The temperature on the surface of the nutrient medium during plasma treatment was within the optimal temperature for lactobacillus growth, i.e. 37.3 ± 0.6°C, which excluded thermal effects. Only a few colonies survived a five-minute treatment. After one-minute treatment, the number of survived colony-forming units was considerably higher. Conclusion. Non-thermal argon plasma treatment proved effective in inhibiting the growth of gram-positive bacteria (Lactobacillus isolated from walnuts) on solid surfaces (agar plates). After five minutes of plasma treatment, the inactivated area (80 mm) exceeded the anode electrode cross section (36 mm) of the plasma generator.

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Широкие перспективы использования нетермальной плазмы атмосферного давления (НТАП) связаны с ее огромным потенциалом уникальных технологических возможностей при создании новых продуктов и технологий. В данной статье представлены результаты экспериментального исследования параметров микроволнового источника НТАП, сочетающего в себе преимущества диэлектрического барьерного разряда и нетермальной плазменной струи.