The combination of plasma-processed air (PPA) and plasma-treated water (PTW) causes synergistic inactivation of Candida albicans SC5314

Microwave-induced plasma was used for the generation of plasma-processed air (PPA) and plasma-treated water (PTW). By this way, the plasma was able to functionalize the compressed air and the used water to antimicrobial effective agents. Their fungicidal effects by single and combined application were investigated on Candida albicans strain SC5314. The monoculture of C. albicans was cultivated on specimens with polymeric surface structures (PE-stripes). The additive as well as the synergistic fungicidal potential of PPA and PTW was investigated by different process windows of plasma exposure time (5-50 s) and sample treatment time with PPA/PTW (1-5 min). For a single PTW or PPA treatment, an increase in the reduction factor with the indicated treatment time was observed (maximum reduction factor of 1.1 and 1.6, respectively). In comparison, the combined application of PTW and then PPA resulted in antagonistic, additive and synergistic effects, depending on the combination. An application of the synergistically acting processes of PTW for cleaning and PPA for drying can be an innovative alternative to the sanitary processes currently used in production plants. © 2020 by the authors

Erforschung plasmachemischer Prozesse zur Polymerisation kolloidaler Systeme, Teilvorhaben Untersuchungen von plasmatechnischen Verfahren zur Polymerisation von micellaren Aggregaten ; Abschlussbericht

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Antimicrobial Effects of Microwave-Induced Plasma Torch (MiniMIP) Treatment on Candida Albicans Biofilms

The susceptibility of Candida albicans biofilms to a non-thermal plasma treatment has been investigated in terms of growth, survival and cell viability by a series of in vitro experiments. For different time periods , the C. albicans strain SC5314 was treated with a microwave-induced plasma torch (MiniMIP). The MiniMIP treatment had a strong effect (reduction factor (RF) = 2.97 after 50 s treatment) at a distance of 3 cm between the nozzle and the superior regions of the biofilms. In addition, a viability reduction of 77% after a 20 s plasma treatment and a metabolism reduction of 90% after a 40 s plasma treatment time were observed for C. albicans. After such a treatment , the biofilms revealed an altered morphology of their cells by atomic force microscopy (AFM). Additionally , fluorescence microscopy and confocal laser scanning microscopy (CLSM) analyses of plasma-treated biofilms showed that an inactivation of cells mainly appeared on the bottom side of the biofilms. Thus, the plasma inactivation of the overgrown surface reveals a new possibility to combat biofilms

Simulation of transient energy distributions in sub-ns streamer formation

Breakdown and streamer formation is simulated in atmospheric pressure nitrogen for a 2D planar electrode system. A PIC code with multigrid potential solver is used to simulate the evolution of the non-equilibrium ionization front on sub-nanosecond timescales. The ion and electron energy distributions are computed, accounting for the inclusion of inelastic scattering of electrons, and collisionally excited metastable production and ionization. Of particular interest is the increased production of metastable and low-energy ions and electrons when the applied field is reversed during the progress of the ionization front, giving insight into the improved species yields in nanosecond pulsed systems

Optimizing the application of plasma functionalised water (PFW) for microbial safety in fresh-cut endive processing

The microbiological profiles and responses of native microflora of endive were investigated using a model process line, to establish where a defined PFW should be optimally applied to retain or improve produce microbiological quality. The PFW processes were compared with tap water and ClO2. The antimicrobial efficacy of PFW was quantified by determining the reduction in microbial load, the microbial viability and vitality. Depending on the stage of application of PFW, up to 5 log10-cycles reduction was achieved, accompanied by a reduction of metabolic activity, but not necessarily with a decrease in metabolic vitality. Multiple application (3-step-PFW-application) was more effective than single application (1-step-PFW-application) and PFW showed stronger antimicrobial effect in pre-cleaned endive. High concentrations of nitrite (315 mg l−1) and nitrate (472 mg l−1) in PFW were the main factors for the antimicrobial efficacy of PFW against bacteria. Furthermore, H2O2 and an acidic pH supported the mechanism of action against the endive microflora. These results identify the pathway to scale up successful industrial application of PFW targeting microbiological quality and safety of fresh leafy products.Industrial relevance The safety, quality and shelf life of freshly cut vegetables, e.g. lettuce, are strongly influenced by the microbial load. In addition, the hygienic design of production line, and a good handling/ production practice are indispensable. This study shows that the application of PFW, as a promising non-thermal sanitation technology, enables the inactivation of native microbial contamination on fresh-cut endive depending on the process stage of application. It further describes the impact of PFW on the metabolic activity and metabolic vitality of the lettuce-associated microflora. For higher acceptance, the mechanism of action of PFW was assumed based on previous chemical analyses and compared to the industrial standard of ClO2. The results contribute to the understanding and product-specificity of PFW-induced effects on safety, quality and shelf life of fresh cut lettuce and could be a basis for a possible industrial implementation and complement of common technologies

Reduce and refine: Plasma treated water vs conventional disinfectants for conveyor-belt cleaning in sustainable food-production lines

Sustainable and microbiologically secure foodstuff production lines are of increasing scientific interest and are in the focus of recent research programs. Additionally, they are of great importance for the production industry due to the prevention of food-borne illnesses caused by pathogens such as Salmonella sp., Listeria monocytogenes, or Escherichia coli. These pathogens are responsible for production losses, loss of customer acceptance, and severe food-borne illnesses. A pathogenic threat is frequently combated with sanitizing steps of the production lines. For conveyor band cleaning, this study compares the cleaning abilities of nitric acid (HNO3) and plasma treated water (PTW), which have been sprayed via a commercially available nozzle on two different polymeric surfaces (polysiloxane and polyurethane). Additionally, the cleaning agents HNO3 and PTW have been characterized through their pH and their conductivity. These findings have been underpinned by experiments that focus on a possible influence of nozzle abrasion, such as brass and stainless-steel nanoparticles, on the antimicrobial potential of PTW and HNO3. Adversely acting effects like an enhanced abrasion of conveyer band materials due to PTW or HNO3 treatment have been checked by using light microscopic micrographs and topographic scans in high-resolution mode. Based on the presented results of the experiments, the suitability of an in-place sanitation step in foodstuff production lines has been demonstrated on a laboratory scale

Efficiency of plasma-processed air for biological decontamination of crop seeds on the premise of unimpaired seed germination

In this study, the antimicrobial effect of plasma-processed air (PPA) generated by a microwave-induced nonthermal plasma was investigated for preharvest utilization using three crop species: Barley, rape, and lupine. Bacillus atrophaeus spores were chosen as a model, inoculated onto seeds, and subsequently treated with PPA at two different flow rates, different filling regimes, and gas exposure times. PPA treatment was efficient in reducing viable spores of B. atrophaeus, reaching sporicidal effects in all species at certain parameter combinations. Maximum germination of seeds was strongly reduced in barley and rape seeds at some parameter combination, whereas it had a modest effect on lupine seeds. Seed hydrophilicity was not altered. Overall, PPA investigated in this study proved suitable for preharvest applications

Characterization of Antimicrobial Effects of Plasma-Treated Water (PTW) Produced by Microwave-Induced Plasma (MidiPLexc) on Pseudomonas fluorescens Biofilms

stract: For the decontamination of surfaces in the food production industry, plasma generated compounds (PGCs) such as plasma-treated water (PTW) or plasma processed air (PPA) offer many promising possibilities for future applications. Therefore, the antimicrobial effect of water treated with microwave-induced plasma (MidiPLexc) on Pseudomonas fluorescensbiofilms was investigated. 10 ml deionized water was treated with the MidiPLexc plasma source for 100 s, 300 s and 900 s (pre-treatment time) and the bacterial biofilms were exposed to the PTW for 1 min, 3 min and 5 min (post treatment time). To investigate the influence of PTW on P. fluorescensbiofilms, microbiological assays (CFU, fluorescence and XTT assay) and imaging techniques (fluorescence microscopy, confocal laser scanning microscopy (CLSM), and atomic force microscopy (AFM)) were used. The CFU showed a maximum reductionof 6 log10 by using 300 s pre-treated PTW for 5 min. Additionally, a maximum reduction of 81 % for the viability of the cells and a 92 % reduction in the metabolic activity of the cells wasachieved by using 900 s pre-treated PTW for 5 min. The microscopic images showed evident microbialinactivation within the biofilm even at the shortest pre-treatment (100s) and post-treatment (1min) times. Moreover,reduction of the biofilm thickness and increased cluster formation within the biofilm wasdetected. Morphologically,the fusion of cell walls intoa uniform dense cell mass. The findings correlated with a decrease inthe pH value of the PTW,which forms the basis for the chemically active components of PTW and its antimicrobial effects. These results, provide valuableinsights into the mechanisms of inactivation of biofilms by plasma generated compounds (PGCs) such as PTW and thus allow forfurther parameter adjustmentfor applications infood industry

Characterization of antimicrobial effects of Plasma-Treated Water (PTW) produced by Microwave-Induced Plasma (MidiPLexc) on pseudomonas fluorescens biofilms

For the decontamination of surfaces in the food production industry, plasma-generated compounds such as plasma-treated water or plasma-processed air offer many promising possibilities for future applications. Therefore, the antimicrobial effect of water treated with microwave-induced plasma (MidiPLexc) on Pseudomonas fluorescens biofilms was investigated. A total of 10 mL deionized water was treated with the MidiPLexc plasma source for 100, 300 and 900 s (pretreatment time) and the bacterial biofilms were exposed to the plasma-treated water for 1, 3 and 5 min (post-treatment time). To investigate the influence of plasma-treated water on P. fluorescens biofilms, microbiological assays (colony-forming units, fluorescence and XTT assay) and imaging techniques (fluorescence microscopy, confocal laser scanning microscopy, and atomic force microscopy) were used. The colony-forming units showed a maximum reduction of 6 log10 by using 300 s pretreated plasma water for 5 min. Additionally, a maximum reduction of 81% for the viability of the cells and a 92% reduction in the metabolic activity of the cells were achieved by using 900 s pretreated plasma water for 5 min. The microscopic images showed evident microbial inactivation within the biofilm even at the shortest pretreatment (100 s) and post-treatment (1 min) times. Moreover, reduction of the biofilm thickness and increased cluster formation within the biofilm was detected. Morphologically, the fusion of cell walls into a uniform dense cell mass was detectable. The findings correlated with a decrease in the pH value of the plasma-treated water, which forms the basis for the chemically active components of plasma-treated water and its antimicrobial effects. These results provide valuable insights into the mechanisms of inactivation of biofilms by plasma-generated compounds such as plasma-treated water and thus allow for further parameter adjustment for applications in food industry. © 2020 by the authors