Inactivation Kinetics of Salmonella typhimurium and Staphylococcus aureus in Different Media by Dielectric Barrier Discharge Non-Thermal Plasma

Inactivation Kinetics of Pathogenic and Nonpathogenic Bacteria Upon In Vitro Treatment With Cold Atmospheric Pressure Plasma (CAPP)

In the present study, selected pathogenic (Salmonella Typhimurium, Escherichia coli, Pseudomonas aeruginosa, Listeria monocytogenes, Bacillus cereus, and Staphylococcus aureus) and nonpathogenic (Pseudomonas fragi, Pseudomonas fluorescens, Brochothrix thermosphacta, Bacillus subtilis, Lactiplantibacillus plantarum, and Leuconostoc mesenteroides) bacteria were subjected in vitro in cold atmospheric pressure plasma (CAPP) treatment for up to 15 min and the changes in the surviving microbial population were determined. Plasma treatments were carried out by a plasma jet device, operating with argon (Ar) as carrier gas under constant flow (4.0 L/min) at a frequency of 1 MHz and an electrical voltage of 2-6 kV. Microbial inactivation data were modelled using linear and nonlinear (Geeraerd, Weibull) models, through which the corresponding kinetic parameters were calculated. After 15 min of exposure to plasma radiation, the total reduction in the bacterial populations was 2.12 log10 CFU mL-1 for P. fragi, 1.77 log10 CFU mL-1 for P. fluorescens, 2.30 log10 CFU mL-1 for B. thermosphacta, 1.58 log10 CFU mL-1 for B. subtilis, 1.31 log10 CFU mL-1 for L. plantarum, 3.80 log10 CFU mL-1 for L. mesenteroides (highest reduction observed), 1.12 log10 CFU mL-1 for S. Typhimurium, 1.18 log10 CFU mL-1 for E. coli, 1.43 log10 CFU mL-1 for L. monocytogenes, 1.32 log10 CFU mL-1 for B. cereus, 0.88 log10 CFU mL-1 for S. aureus, and 0.73 log10 CFU mL-1 for P. aeruginosa. The results showed a higher reduction in the population of nonpathogenic microorganisms compared to pathogens. The relatively small decrease in the inactivation of bacteria indicates that parameter optimization is necessary to be considered to improve the efficacy of the treatment.

Sublethally injured microorganisms in food processing and preservation: Quantification, formation, detection, resuscitation and adaption

Sublethally injured state has been recognized as a survival strategy for microorganisms suffering from stressful environments. Injured cells fail to grow on selective media but can normally grow on nonselective media. Numerous microorganism species can form sublethal injury in various food matrices during processing and preservation with different techniques. Injury rate was commonly used to evaluate sublethal injury, but mathematical models for the quantification and interpretation of sublethally injured microbial cells still require further study. Injured cells can repair themselves and regain viability on selective media under favorable conditions when stress is removed. Conventional culture methods might underestimate microbial counts or present a false negative result due to the presence of injured cells. Although the structural and functional components may be affected, the injured cells pose a great threat to food safety. This work comprehensively reviewed the quantification, formation, detection, resuscitation and adaption of sublethally injured microbial cells. Food processing techniques, microbial species, strains and food matrix all significantly affect the formation of sublethally injured cells. Culture-based methods, molecular biological methods, fluorescent staining and infrared spectroscopy have been developed to detect the injured cells. Cell membrane is often repaired first during resuscitation of injured cells, meanwhile, temperature, pH, media and additives remarkably influence the resuscitation. The adaption of injured cells negatively affects the microbial inactivation during food processing.

Disinfection of corona and myriad viruses in water by non-thermal plasma: a review

Nowadays, in parallel to the appearance of the COVID-19 virus, the risk of viruses in water increases leading to the necessity of developing novel disinfection methods. This review focuses on the route of virus contamination in water and introduces non-thermal plasma technology as a promising method for the inactivation of viruses. Effects of essential parameters affecting the non-thermal discharge for viral inactivation have been exposed. The review has also illustrated a critical discussion of this technology with other advanced oxidation processes. Additionally, the inactivation mechanisms have also been detailed based on reactive oxygen and nitrogen species.

Review on inactivation of airborne viruses using non-thermal plasma technologies: from MS2 to coronavirus

Although several non-thermal plasmas (NTPs) technologies have been widely investigated in air treatment, very few studies have focused on the inactivation mechanism of viruses by NTPs. Due to its efficiency and environmental compatibility, non-thermal plasma could be considered a promising virus-inactivation technology. Plasma is a partly or fully ionized gas including some species (i.e., electrons, free radicals, ions, and neutral molecules) to oxidize pollutants or inactivate harmful organisms. Non-thermal plasmas are made using less energy and have an active electron at a much higher temperature than bulk gas molecules. This review describes NTPs for virus inactivation in indoor air. The different application processes of plasma for microorganism inactivation at both laboratory and pilot-scale was also reviewed This paper reports on recent advances in this exciting area of viral inactivation identifying applications and mechanisms of inactivation, and summarizing the results of the latest experiments in the literature. Moreover, special attention was paid to the mechanism of virus inactivation. Finally, the paper suggests research directions in the field of airborne virus inactivation using non-thermal plasma.

Inactivation kinetics and cell envelope damages of foodborne pathogens Listeria monocytogenes and Salmonella Enteritidis treated with cold plasma

In recent years, more attention has been paid to the application of cold plasma (CP) in eliminating foodborne pathogenic bacteria. This work investigated CP effects on inactivation kinetics and cell envelopes of Listeria monocytogenes (L. monocytogenes) and Salmonella Enteritidis (S. Enteritidis). Bacterial suspensions were treated with dielectric barrier discharge atmospheric CP at 75 kV for different treatment time. Three regression models were tested for estimating inactivation kinetics. Reactive species generated in plasma, the appearance and integrity of bacterial cells, the activity and secondary structure of enzymes in the cell envelope, and molecular docking, were measured for evaluating the envelope damages. Results indicated that Log-linear model was suitable for L. monocytogenes and the Weibull model was suitable for S. Enteritidis. S. Enteritidis was more sensitive to short-lived reactive species (such as OH radicals) in plasma than L. monocytogenes, and the cell envelope of S. Enteritidis was more severely damaged (the increased membrane permeability and leakage of intracellular substances) after plasma treatment. Interestingly, compared with S. Enteritidis, the decrease in the activity of enzymes existing in the cell envelope of L. monocytogenes did not contribute significantly to the death of bacteria. Molecular docking further suggested that the decrease in the enzyme activity might be due to the modification of the enzyme, by the interaction between reactive species in plasma (H₂O₂) and amino acid residues of the enzyme through the hydrogen bond.

A Population Balance Model to Describe the Evolution of Sublethal Injury

The detection and quantification of sublethal injury (SI) of pathogenic microorganisms has become a common procedure when assessing the efficiency of microbial inactivation treatments. However, while a plethora of studies investigates SI in function of time, no suitable modelling procedure for SI data has been proposed thus far. In this study, a new SI model structure was developed that relies on existing microbial inactivation models. This model is based on the description of inactivation kinetics between the subpopulations of healthy, sublethally injured and dead cells. The model was validated by means of case studies on previously published results, modelled by different inactivation models, i.e., (i) log-linear inactivation; (ii) biphasic inactivation; and (iii) log-linear inactivation with tailing. Results were compared to those obtained by the traditional method that relies on calculating SI from independent inactivation models on non-selective and selective media. The log-linear inactivation case study demonstrated that the SI model is equivalent to the use of independent models when there can be no mistake in calculating SI. The biphasic inactivation case study illustrated how the SI model avoids unrealistic calculations of SI that would otherwise occur. The final case study on log-linear inactivation with tailing clarified that the SI model provides a more mechanistic description than the independent models, in this case allowing the reduction of the number of model parameters. As such, this paper provides a comprehensive overview of the potential and applications for the newly presented SI model.

Dielectric barrier discharge cold atmospheric plasma: Influence of processing parameters on microbial inactivation in meat and meat products

Decontamination of meat is commonly practiced to get rid of or decrease the microbial presence on the meat surface. Dielectric barrier discharge cold atmospheric plasma (DBD-CAP) as innovative technology is a food microbial inactivation technique considered in high regard by food scientists and engineers in present times. However, cold atmospheric plasma application is at the experimental stage, due to lack of sufficient information on its mode of action in inactivating microbes, food shelf-life extensibility, whereas, the nutritional value of food is preserved. In this review, we have appraised recent work on DBD-CAP concerning the decontamination treatment of meat products, highlighting the processing value results on the efficacy of the DBD-CAP microbial inactivation technique. Also, the paper will review the configurations, proposed mechanisms, and chemistry of DBD-CAP. Satisfactory microbial inactivation was observed. In terms of DBD-CAP application on sensory evaluation, inferences from reviewed literature showed that DBD has no significant effect on meat color and tenderness, whereas in contrast, TBARS values of fresh and processed meat are affected. DBD seems economically efficient and environmentally sustainable.