Plasma-activated water (PAW) is a liquid enriched with reactive oxygen and nitrogen species (RONS), which impart antimicrobial and bioactive properties. In this study, PAW generated in liquid or gas phase under nitrogen or oxygen atmospheres was characterized in terms of pH, electrical conductivity, oxidation-reduction potential, surface tension, and concentrations of H₂O₂ and NO₂⁻. Hydroxyl radical (•OH) formation was confirmed using DIPPMPO as a spin-trapping probe, while antioxidant activity was determined directly in treated water for the first time. The stability of reactive species was assessed over three months at room temperature, 4 °C, and −18 °C. Results indicate that plasma effects on physicochemical parameters depend strongly on the process gas. From a long-term storage perspective, samples maintained at 4 °C stabilized at higher H₂O₂ and NO₂⁻ concentrations. Antioxidant activity persisted for up to 60 days, though at low levels. EPR analysis revealed that hydroxyl radical concentration increased slightly during storage, with 60-day samples showing higher signal intensities compared to fresh PAW. Overall, the findings provide new insights into PAW composition, radical dynamics, and stability, highlighting the influence of gas atmosphere and storage conditions on its properties and supporting its potential for applications in the food, agriculture, and biomedical sectors.

The food processing industry is seeking new technologies to enhance product safety, extend shelf life, and optimise food quality in response to growing consumer demand for high-quality products. Since the discovery of plasma technology, its potential applications in food processing have been numerous. For most of these applications, plasma characterisation is key to successfully scaling up from laboratory to industrial settings. A highly valuable tool for plasma characterisation is optical emission spectroscopy (OES), which serves as a non-invasive diagnostic method to monitor reactive species, specifically excited atoms and molecules (reactive oxygen and nitrogen species—RONS) that are critical for food treatment. The main role of OES in food control is to enable species identification and real-time process monitoring, providing feedback on electron temperature and density to prevent thermal damage to sensitive food products. It also facilitates optimisation by adjusting voltage and gas flow rates to maximise the production of antimicrobial species. These results ensure that processes are reliable and repeatable, supporting the transition from laboratory-scale to industrial applications. The paper provides an overview of the use of optical emission spectroscopy in various applications of plasma technology in food processing, including the determination of the elemental composition of raw materials and final products, detection of contaminants, quality control, determination of characteristic plasma parameters, and ensuring compliance with food safety regulations.

Agricultural by-products, such as tomato peels and sugar beet leaves, represent valuable sources of bioactive compounds that can be efficiently recovered using advanced extraction techniques. This study investigated the efficiency of high-voltage electrical discharge (HVED) extraction of bioactive compounds and antioxidant properties from tomato peel (TP) and sugar beet leaves (SBLs). The target compounds were total phenolic content (TPC), lycopene, β-carotene, and chlorophylls. HVED treatments of 1, 3, and 5 min were applied using 30% and 50% methanolic solutions. A 5 min treatment enhanced the extraction of lycopene (2.04 mg/100 mL) and β-carotene (1.14 mg/100 mL) in the 50% methanolic solution, while the shorter 3 min treatments increased TPC (0.117 mg GAE/mL in TP; 0.280 mg GAE/mL in SBLs) and chlorophyll content (25.47 mg/100 mL). For both TP and SBLs, the more concentrated methanolic solvent (50%) was more efficient in extracting bioactive components than the 30% solution. Electron paramagnetic resonance (EPR) spectroscopy confirmed increases in antioxidant activity in all treated samples, with the highest values of 45.27% for TP and 53.16% for SBLs. As a direct and sensitive technique for detecting free-radical scavenging, EPR proved highly suitable for evaluating the impact of HVED treatments. Overall, HVED demonstrated strong potential as a green and effective method for enhancing the recovery of valuable bioactives and antioxidant properties from tomato and sugar beet by-products.