Plasma-treated water (PTW) possess anti-microbial potential against
, which is observable for both suspended cells and cells organized in biofilms. Against that background, the chemical composition ...of PTW tends to focus. Various analytical techniques have been applied for analyses, which reveal various traceable reactive oxygen and nitrogen compounds (RONS). Based on these findings, it is our aim to generate a PTW analog (anPTW), which has been compared in its anti-microbial efficiency with freshly generated PTW. Additionally, a solution of every traceable compound of PTW has been mixed according to their PTW concentration. As references, we treated suspended cells and mature biofilms of
with PTW that originates from a microwave-driven plasma source. The anti-microbial efficiency of all solutions has been tested based on a combination of a proliferation, an XTT, and a live-dead assay. The outcomes of the test proved an anti-microbial power of PTW that suggests more active ingredients than the traceable compounds HNO
, HNO
, and H
O
or the combined mixture of the analog.
This study evaluated the impact of a defined plasma treated water (PTW) when applied to various stages within fresh-cut endive processing. The quality characteristic responses were investigated to ...establish the impact of the PTW unit processes and where PTW may be optimally applied in a model process line to retain or improve produce quality. Different stages of application of PTW within the washing process were investigated and compared to tap water and chlorine dioxide. Fresh-cut endive (
L.) samples were analyzed for retention of food quality characteristics. Measurements included color, texture, and nitrate quantification. Effects on tissue surface and cell organelles were observed through scanning electron and atomic force microscopy. Overall, the endive quality characteristics were retained by incorporating PTW in the washing process. Furthermore, promising results for color and texture characteristics were observed, which were supported by the microscopic assays of the vegetal tissue. While ion chromatography detected high concentrations of nitrite and nitrate in PTW, these did not affect the nitrate concentration of the lettuce tissue post-processing and were below the concentrations within EU regulations. These results provide a pathway to scale up the industrial application of PTW to improve and retain quality characteristic retention of fresh leafy products, whilst also harnessing the plasma functionalized water as a process intervention for reducing microbial load at multiple points, whether on the food surface, within the process water or on food-processing surfaces.
Methods, which use an indirect plasma treatment for the inactivation of microorganisms in foods, claim a vastly growing field of research. This paper presents a method that uses plasma-processed air ...(PPA) as a sanitizer. In addition to a sanitation concept for the decontamination of produce in the value chain, the presented method offers a possible application as an “in-process” surface sanitation. PPA provides antimicrobial-potent species, which are predominantly reactive nitrogen species (RNS); this has an outstanding groove penetration property. In an experimental approach, surfaces, made from materials, which are frequently used for the construction of food-processing plants, were inoculated with different microorganisms. Listeria monocytogenes (ATCC 15313), Staphylococcus aureus (ATCC 6538), Escherichia coli (ATCC 10538), Salmonella enterica subsp. enterica serovar Typhimurium (ATCC 43971), and Salmonella enterica subsp. enterica serovar Enteritidis (ATCC 13076) are all microorganisms that frequently appear in foods and possess the risk for cross-contamination from the plant to the produce or vice versa. The contaminated samples were treated for various treatment times (1–5 min) with PPA of different antimicrobial potencies. Subsequently, the microbial load on the specimens was determined and compared with the load of untreated samples. As a result, reduction factors (RF) up to several log10-steps were obtained. Although surface and the bacterial strain showed an influence on the RF, the major influence was seen by a prolongation of the treatment time and an increase in the potency of the PPA.
Plasma medicine and also decontamination of bacteria with physical plasmas is a promising new field of life science with huge interest especially for medical applications. Despite numerous successful ...applications of low temperature gas plasmas in medicine and decontamination, the fundamental nature of the interactions between plasma and microorganisms is to a large extent unknown. A detailed knowledge of these interactions is essential for the development of new as well as for the enhancement of established plasma‐treatment procedures. In the present work we introduce for the first time a growth chamber system suitable for low temperature gas plasma treatment of bacteria in liquid medium. We have coupled the use of this apparatus to a combined proteomic and transcriptomic analyses to investigate the specific stress response of Bacillus subtilis 168 cells to treatment with argon plasma. The treatment with three different discharge voltages revealed not only effects on growth, but also clear evidence of cellular stress responses. B. subtilis suffered severe cell wall stress, which was made visible also by electron microscopy, DNA damages and oxidative stress as a result of exposure to plasma. These biological findings were supported by the detection of reactive plasma species by OES measurements.
The synergistic antimicrobial effects of plasma-processed air (PPA) and plasma-treated water (PTW), which are indirectly generated by a microwave-induced non-atmospheric pressure plasma, were ...investigated with the aid of proliferation assays. For this purpose, microorganisms (
,
,
, sporulated
) were cultivated as monocultures on specimens with polymeric surface structures. Both the distinct and synergistic antimicrobial potential of PPA and PTW were governed by the plasma-on time (5⁻50 s) and the treatment time of the specimens with PPA/PTW (1⁻5 min). In single PTW treatment of the bacteria, an elevation of the reduction factor with increasing treatment time could be observed (e.g., reduction factor of 2.4 to 3.0 for
). In comparison, the combination of PTW and subsequent PPA treatment leads to synergistic effects that are clearly not induced by longer treatment times. These findings have been valid for all bacteria (
>
=
). Controversially, the effect is reversed for endospores of
. With pure PPA treatment, a strong inactivation at 50 s plasma-on time is detectable, whereas single PTW treatment shows no effect even with increasing treatment parameters. The use of synergistic effects of PTW for cleaning and PPA for drying shows a clear alternative for currently used sanitation methods in production plants. Highlights: Non-thermal atmospheric pressure microwave plasma source used indirect in two different modes-gaseous and liquid; Measurement of short and long-living nitrite and nitrate in corrosive gas PPA (plasma-processed air) and complex liquid PTW (plasma-treated water); Application of PTW and PPA in single and combined use for biological decontamination of different microorganisms.
Gentle sanitation of fresh fruits and vegetables is highly demanded. Currently used methods lead to losses in product amounts and quality. Furthermore, these methods go along with high costs and ...chemical residues. One reason for such problems is microbial contamination. Due to the fact that conventional decontamination processes are not suitable for preservation of fresh produce, alternatives such as plasma technology can be helpful. Three different artificial specimen and seeds of Brassica napus were contaminated with endospores of Bacillus atrophaeus and afterwards plasma treated directly with DBD plasma and indirectly with microwave plasma processed air. After a treatment time of 15 minutes reduction rates between 0.5 and 5.2 log were achieved. The viability of seeds was not affected. The advantages of plasma and promising results offer a wide range of possible uses in food industry.
The antimicrobial efficacy of a dielectric barrier discharge (DBD) and a microwave plasma setup against Bacillus atrophaeus spores on biological and non‐biological surfaces is investigated. Moreover, the establishment of a non‐biological specimen for the comparability of different plasma techniques is shown. The decontamination efficiency raised up to 5.2 log cfu/specimen by plasma treatment.
An innovative device capable of generating a cold atmospheric pressure plasma inside a 5 m long flexible tube with 2 mm inner diameter is presented. In order to analyze the inner‐tube plasma, optical ...emission spectroscopy in the (vacuum) ultraviolet spectral range and Fourier transformed infrared spectroscopy were performed. By admixing small concentrations of nitrogen and oxygen to the standard argon gas flow rate of 1.5 slm, a drastically change in the plasma composition was observed. Additionally, it is possible to form a jet‐like plasma at the end of the tube. The microbicidal efficacy of the inner‐tube plasma and the jet‐like plasma was shown for Bacillus atrophaeus spores.
In this paper a setup is presented, to generate a DBD inside a long, flexible and thermo labile tube with the purpose to decontaminate the inner tube walls. The main application for these modified tubes is the implementation as biopsy channels in endoscopes, which are highly contaminated and difficult to sterilize. Besides decontamination of the inner tube it is also possible to ignite a jet‐like discharge at the tube end.
The decontamination efficiency of a non-thermal remote plasma application for dry and heat sensitive products was investigated. Therefore three different types of herbs and spices (pepper seeds, ...crushed oregano and paprika powder) with various surface-to-volume ratios were treated with plasma processed air up to 90min and the inactivation of their native microbial flora was examined. Furthermore the impact of the plasma treatment on the product color was determined. The remote plasma treatment reduced the native microbial flora of the pepper seeds and the paprika powder by more than 3log10 after 60min treatment time. However remote plasma treatment of red paprika powder resulted in a considerable loss of redness after a treatment time of ⩾5min. The lower inactivation of the native microbial flora of oregano of 1.6log10, was related to the much lower initial microbial load. The treatment had only a minor impact on the pepper seed’s and oregano’s color (ΔE∗ up to 10.2 and 20.0, respectively).
Plasma-generated compounds conceived by microwave-induced plasma (MidiPLexc) were physicochemically investigated in their molecular compositions. Therefore, plasma-treated water (PTW) was generated ...by treatment with the MidiPLexc within a 1 l glass bottle for a pre-treatment time of 100 s, 300 s and 900 s. The PTW was further investigated in its composition of reactive oxygen/nitrogen species. For this purpose, the hydrogen peroxide (H2O2) concentration of the PTW was determined electrochemically using chronoamperometry, and the anionic components were determined using ion chromatography. As a result, H2O2 concentrations of up to 720 mg l−1, nitrite concentrations of 1600 mg l−1 and nitrate concentrations of 72.3 mg l−1 could be detected after 900 s pre-treatment time of the water. The compounds obtained by ion chromatography were fractionated and subsequently confirmed by mass spectrometry. Once an overview of the chemical composition of PTW had been obtained, its effects on pathogens like Pseudomonas fluorescens and L. monocytogenes, which are both of particular importance as pathogenic contaminants during food production, were tested. In that process, a maximum reduction in the colony forming units of 4 log10 steps for P. fluorescens and 3 log10 steps for L. monocytogenes could be observed. The LIVE/DEAD assay showed a maximum reduction in the ratio G/R of 67% for P. fluorescens and 38% for L. monocytogenes. In addition, the XTT assay results showed a maximum cell metabolism reduction of 96% for P. fluorescens and 91% for L. monocytogenes.
The biological effects of atmospheric cold plasma generated reactive species are mediated through and at a liquid interface. The diversity of antimicrobial efficacy or intensity of effects may differ ...with respect to the plasma device or set up, and it is important to understand how these differences occur to advance understanding and successful applications. Thus, plasma treated water (PTW) from a microwave driven plasma source (PTW‐MW) and plasma treated water from a di‐electric barrier discharge system (PTW‐DBD) were compared in terms of long lived reactive species chemical composition and antimicrobial activity. The influence of a post‐treatment storage time (PTST), where reactive species in the gas phase were maintained in contact with the liquid was investigated. Nitrogen‐based chemistry dominated in PTW‐MW, with high concentrations of nitrous acid decomposing to nitrite and nitrate, while H2O2 and nitrate were predominant in PTW‐DBD. PTST could enhance H2O2 concentrations in di‐electric barrier PTW over time while nitrous acid, the main oxidative species in microwave driven PTW, decreased. This work highlights that plasma treated water presents a resource comprising a range of different compounds, stabilities and reactivities which may be tunable to specific applications.
A dielectric barrier discharge (DBD) and a microwave (MW) plasma source generate plasma treated water (PTW) with distinct chemical composition and different antimicrobial efficacy. A post‐treatment storage time in gas sealed conditions modulates the reactive species evolution, with hydrogen peroxide as main oxidative species increasing in PTW‐DBD and nitrous acid decomposing to nitrate in PTW‐MW.
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