Plasma-Assisted Extraction of Bioactive Compounds from Tomato Peels and Sugar Beet Leaves Monitored by Electron Paramagnetic Resonance Spectroscopy

Abstract

Featured Application: High-voltage electrical discharge (HVED) represents a promising non-thermal, environmentally friendly technology with strong potential for future applications in the extraction of valuable bioactive compounds from agricultural by-products. Its ability to enhance mass transfer, reduce solvent use, and operate under mild conditions makes HVED an attractive tool for developing sustainable extraction methods in the food, nutraceutical, and biorefinery sectors. In parallel, electron paramagnetic resonance (EPR) spectroscopy offers considerable potential as an advanced analytical technique for real-time monitoring of radical formation, oxidative processes, and the overall impact of emerging extraction technologies on product quality. The combined use of HVED and EPR provides new insights into the design, optimization, and quality control of next-generation green extraction processes, supporting the transition toward a circular and resource-efficient bioeconomy. 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.