Aplicação de plasma frio por descarga luminosa na inativação de Salmonella enterica e Escherichia coli em agrião (Nasturtium officinale R. Br)

Abstract

This study evaluated the efficacy of cold plasma generated by glow discharge for the inactivation of Salmonella enterica serovar Typhimurium and Escherichia coli inoculated in watercress (Nasturtium officinale R.Br.), as well as to investigate its effects on cellular viability, microbiological stability during refrigerated storage, and plasma-induced morphological alterations. Plasma treatments were carried out under different operational conditions, varying gas flow rates (10, 20, and 30 mL/min) and exposure times (10, 15, and 20 min). Microbial survival was monitored throughout refrigerated storage by selective plate counts. Residual cellular viability was assessed using the MTT assay, and structural damage was examined by scanning electron microscopy (SEM). The results demonstrated that cold plasma treatment promoted significant pathogen inactivation, with complete elimination of cultivable E. coli and S. Typhimurium in watercress under the most effectve conditions, which were F10T20, F20T20 and F30T20 for E. coli and F10T10, F10T15 and F20T10 for S. Typhimurium. Intermediate treatments also resulted in significant reductions (p < 0.05). When microbial suspensions were treated independently of the food matrix, total inactivation was achieved under all evaluated conditions. The MTT assay confirmed a substantial loss of metabolic activity, with residual viability ranging from 7.68 ± 0.38% to 1.60 ± 0.72% for E. coli and from 17.71 ± 0.94% to 1.46 ± 0.39% for S. Typhimurium, showing a progressive decrease over 72 h of refrigerated storage. SEM images revealed pronounced plasma-induced morphological damage, including cell shrinkage, increased surface roughness, membrane fissures, and structural collapse of bacterial cells. These effects are consistent with oxidative membrane disruption driven by reactive oxygen and nitrogen species generated during plasma discharge. Overall, the findings demonstrate that cold glow discharge plasma is an effective non-thermal intervention for the control of S. Typhimurium and E. coli in leafy vegetables, highlighting its potential application as an alternative decontamination strategy for fresh produce.