Plasma-driven oxidative modification of quercetin and its antibacterial application on cherry tomato

Quercetin, a widely distributed natural flavonol, is well known for its antioxidant properties, but can act as a pro-oxidant under certain conditions, promoting oxidative stress and generating reactive oxygen species (ROS). This transition to a pro-oxidant state enables quercetin to exert potent antibacterial activities. In this study, cold plasma treatment was employed to induce the pro-oxidant conversion of quercetin, and the antibacterial efficacy, underlying antibacterial mechanisms of plasma-activated quercetin (PAQ), and its applicability for the decontamination of cherry tomatoes were evaluated. PAQ effectively inactivated Escherichia coli O157:H7, Salmonella Typhimurium and Listeria monocytogenes, achieving reductions below the detection limit (> 5. 19 log reduction) at an optimal concentration of 75 μM with 20 min of plasma treatment. FT-IR and UV-Vis analyses revealed a hypsochromic shift, indicating the oxidative transformation of quercetin into quinone forms. PAQ treatment significantly (P < 0.05) increased cell membrane damage, reduced metabolic enzyme activity, and elevated intracellular ROS levels in all three pathogens through the generation of hydrogen peroxide and singlet oxygen. When applied to cherry tomatoes, PAQ treatment achieved more than 3 log reduction of pathogens on cherry tomato surface, which was significantly (P < 0.05) greater than those of the individual treatments, without adversely affecting quality. Moreover, PAQ maintained its antimicrobial activity over five reuse cycles. These findings demonstrate that plasma activation converts quercetin into a pro-oxidant form, enabling sustained ROS-mediated bacterial inactivation and supporting its application for improving the microbial safety of cherry tomatoes.