The plasma jet technique, a popular method for generating reactive oxygen and nitrogen species through an inert gas (such as Ar) mixed with air, was investigated. A plasma jet model was developed from a selection of statistical data, and the resulting NO, OH, and H2O2 concentrations were examined. The objective of the study was to establish a simple 2D plasma jet module and to mathematically understand the involved chemical reactions through the Multiphysics (finite element method) program. Determination of optimized conditions via the design of experiment method was performed. To create new responses, three nominal concentrations (NO, OH, and H2O2) were used to measure the performance of the species product. A full factorial design based on two levels, or 23 runs, with three central points and two replications was employed in the simulations using COMSOL Multiphysics 5.3a software. The main effects and interactions between the variables were identified for three main parameters: gas velocities of 40–70 m/s, plasma gaps of 10–30 mm, and simulation times of 2.8–4 ms. These parameters were selected to unravel design possibilities with external variables, which can significantly contribute to the process of designing a prototype of a cell-scaled plasma jet model.

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This study was aimed to determine the effects of a plasma jet of mixed argon and oxygen (Ar‐O2) on Aspergillus flavus growth in potato dextrose broth (PDA). Settings for power, discharge duration, and gas flow rate of the plasma jet system (PJS) were optimized over ranges of 10–20 W, 1–10 min, and 3–9 L/min, respectively. The optimal conditions required to inhibit 100% of A. flavus growth at 30°C for 48 hr were 20 W, 10 min, and 9 L/min, respectively. The PJS inhibited 100% of the A. flavus growth in 20 replicates of infected peeled peanuts. Aspergillus flavus cell walls were destroyed via lipid and cell membrane oxidization, resulting in lost osmotic capability and damaged DNA and enzymes. However, the PJS is limited by a short exposure distance. More power, longer exposure, and increased gas flow might be needed to increase the distance while maintaining 100% microbial growth inhibition. Application to real foods and agricultural products, and upscaling the PJS for industrial use will be assessed in further studies. Practical applications Our proposed plasma system could be applied to postharvested agricultural products such as dried peanuts and chili. However, the technology will require validation before it can be applied in an industrial scale.

HighlightsAbstract. In this study, we developed an effective methodology to determine the suitable plasma-based generating system of reactive nitrogen species (RNS) targeting hydroponic farming systems using a full factorial design with center points and blocking. A 2k with 2 blockings plus 2 center points design was employed in the experiment to develop an efficient analytical model for nitrogen solution concentration and hydroponic vegetable growth incorporating the plasma discharge system process parameters, including water flow rate, plasma discharge duration, and air flow rate. This study designed and constructed an air plasma discharge system with DC power supply. Thereafter, nitrogen solution was generated under a parameter conditions setting by the design of experiments (DOE) method. RNS solution, which contained nitrate (NO3-) and nitrite (NO2-) ions with P and K added, was passed through the hydroponic system for growing green oak lettuce. The most promising plasma-generated nitrogen solution parameters were obtained for this set up at a water flow rate of 6 L/min, discharge duration of 60 min, and activated air flow rate of 60 mL/min. Keywords: Nitrate, Nitrite, Plasma discharge, Reactive nitrogen species.

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