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.
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.
•Plasma functionalised water (PFW) successfully used as wash water additive on lettuce.•PFW treatment enhances the microbiological safety of fresh-cut endive.•PFW showed promising results compared to industry standard chlorine dioxide (ClO2).•Mechanism of action of PFW based on reactive oxygen/nitrogen species (RONS).
The decontamination and sanitation methods currently used are mainly antimicrobial ineffective, generate high costs with a high consumption of water and chemicals (additives). As an alternative, ...non-thermal plasma at atmospheric pressure could be a versatile tool. Therefore, a pilot-scaled set-up based on a microwave-plasma source that generates plasma processed air (PPA), a gaseous mixture which contains manifold RNS-based chemical compounds gaining, among others, the antimicrobial effectivity of that mixture. The PPA was introduced to a water-processing device (WPD) to enrich tap water. By this way, plasma processed tap water (PPtW), which can be applied for the decontamination of packaging material, fresh produce and processing equipment, was generated. This is a new and innovative method for the generation of antimicrobial active plasma processed water. In our experiments, the native contamination of fresh-cut lettuce treated with PPtW in a common washing process and the microbial load of the washing water itself was investigated. Different treatment scenarios showed the influence of PPtW to the fresh-cut lettuce and the washing water as well as the hygienic problems of recontamination during the washing process. The characteristics of plasma and its generated cocktail of long living chemical compounds in air and in water leading to a significant bacterial inactivation and offering a wide range of possible applications.
The safety, quality and shelf life of freshly cut vegetables greatly depend on the microbial load, especially with phyto and human pathogens, of the produce as well as the hygienic design of production device and good handling and production practice. This study shows that the application of PPW/PPtW, as a promising non-thermal sanitation technology, enables the inactivation of native contamination on fresh-cut lettuce in industrial relevant level. It further describes the impact of the necessity of hygienic environment during production to avoid cross- and re-contamination. The results contribute to the understanding and product-specificity of PPW-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.
•Pilot-plant scale fresh-cut lettuce rinsing/washing unit based on plasma technology•PPW as ‘on demand’ antimicrobial agent based on non-thermal atmospheric pressure plasma technology•Technical trial with 45kg fresh-cut lettuce and ~1.500l of plasma generated disinfectant•Enhancement of microbial reduction up to 2lg cycles in a single washing stage•Advantages of PPW offer a wide range of possible uses for sanitation in food industry
The antimicrobial effectiveness of non-thermal plasma is scientifically accepted. Applications can be found in medicinal sterilisation processes. However, the effects of plasma treatments on plant ...food with regard to nutritional value are not yet sufficiently investigated. To study the interactions of plasma immanent reactive species with secondary plant metabolites, lamb’s lettuce (Valerianella locusta) was exposed to an atmospheric pressure plasma jet. Changes in the phenolic profile were compared to experiments with pure substances to determine the influence of the food matrix. Whereas pure flavonoids showed a strong time-dependent decrease, not originating from photo- or thermodesorption processes, the content of diosmetin in lamb’s lettuce significantly increased. Regarding phenolic acids, plasma exposure led to a strong reduction in lamb’s lettuce, while the concentration of pure monophenols changed little within the same period of time. Treatments with plasma-similar temperatures and UV radiation suggest that due to plasma-reactive species concomitant disintegration of cell membranes and oxidation of released cellular compounds are taking place. Time-dependent changes of the leaf surface morphology due to plasma-induced erosion have been observed by scanning electron microscopy.
► The mobility of CeO2 nanoparticles is impacted by solution chemistry. ► Transport of CeO2 nanoparticles is significantly hindered at acidic pH and high ionic strength. ► Re-entrainment of deposited CeO2 nanoparticles cannot be accomplished by changing solution chemistry. ► CeO2 nanoparticles can show partial breakthrough under neutral and alkaline pH and ionic strength below 10 mM. ► A mathematical model is developed for predicting the mobility of CeO2 nanoparticles through packed beds.
For an enhanced tuning of an external-cavity Littrow diode laser at 670 nm a new approach based on the frequency controlling of intra-cavity acousto-optic modulators (AOM) has been developed and ...tested. Using a method called “mode shaking” a nearly continuously laser tuning over a frequency range of 186 GHz (0.279 nm) within a time interval of 20 ms has been achieved. A further method called “far laser frequency jump” allows frequency changes of up to 1080 GHz (1.6 nm) between two spectral regions of the diode laser emission range within about 50 μs.
The working group “Food technology and safety” of the DFG Senate Commission on Food Safety (SKLM) advises on new technologies concerning food processing. Treatment with plasma is a newly developed ...process, which is currently used only on a pilot scale in Europe. The novel plasma treatment technology is experimentally applied to consumer goods. There are also potential applications in the food sector, e.g. to inactivate microorganisms on food surfaces. There is still insufficient information on concomitant physical and chemical processes and changes induced in the food. On May 25th 2012, the SKLM issued a first statement on plasma treatment of foods in German. The English version was agreed on December 14th 2012.
Herbal teas can cause diseases, when their naturally high microbial load is not inactivated via proper brewing. Cold plasma as effective and gentle decontamination technique was investigated for ...dried peppermint, stinging nettle, and lemongrass.
Microwave-driven plasma processed air (up to 7.5 min) significantly reduced total viable counts up to 1.6 log10 CFU/g (initial counts were 8.02, 7.43, and 7.44 log10 CFU/g for peppermint, stinging nettle, and lemongrass, respectively). Spore-forming bacteria, Enterobacteriaceae, yeasts, and molds were inactivated up to 2 log10 CFU/g. MALDI-ToF MS analyses showed a 30–100% reduction in microbial diversity as result of the plasma treatment. Color of most samples was visibly reduced in greenness and antioxidants, phenols, flavonoids, and free amino groups mostly decreased by plasma treatment.
Overall, use of plasma processed air could be a suitable tool to decontaminate dried herbs at larger scale but has to be improved by testing different sources, gases, or times.
Cold atmospheric plasma can inactivate herb-associated microorganisms. Its possible effect on quality parameters such as flavor, color or phenolic content should be further studied and reduced, as particularly gentle decontamination processes that preserve the natural appearance of the food are accepted by the consumer. It seemed, that the intensity of the treatment can be reduced by pulsed plasma applications. There is great potential for application on an industrial scale. Peppermint seems to be the most suitable in this context, as it showed the highest microbial reduction together with low quality changes and is widely used, including in so-called cold brew teas, which require particular safety.
•Cold plasma decreased total viable count of peppermint from 8.0 to 6.4 log10 CFU/g.•MALDI-Tof MS revealed 30–100% reduction of microbial diversity through cold plasma.•Cold plasma caused a visible decrease in greenness due to chlorophyll degradation.•Phenolics, flavonoids, and free amino groups remained constant for peppermint.•Pulsed plasma treatment seemed to be better suitable than continuous treatment.
As food of animal and plant origin is prone to microbial spoilage, its production must be monitored and conducted safely to avoid consumer hazards. At the same time, environmental and sustainability ...aspects are becoming increasingly important. In this study, washing of food conveyor belts at ambient temperature was performed with plasma-processed water (PPW) and an optical detector to monitor the cleaning success. The microbial plate counts could be reduced with pressurized water, foam and PPW by >3 log10 CFU/cm2, similar to the standard industrial washing with amine-based disinfectant (Neoseptal®, Dr. Weigert, Germany). However, PPW degrades to naturally occurring substances, and the inactivation time was reduced from 15 to 1 min. The optical detector could mostly distinguish between uncleaned and cleaned belts. The fast, precise and easy applicable measurement could be integrated into the production line for automated monitoring, which could result in cleaning cycles based on demand.
An on-demand cleaning process with less need for chemicals would save time and money plus protect the environment. Plasma-processed water is as effective as a chemical disinfectant combined with a reduced decontamination time (from 15 to 1 min) and free of complex chemical compounds. The optical detector can be used inline, fast and easy for automated hygiene monitoring in the food production.
•Plasma-processed water (PPW) reduced microbial plate counts from 4 to 1 log10 CFU/cm2•Decontamination time was reduced from 15 (amine-based disinfectant) to 1 min (PPW).•PPW was as effective as standard cleaning and degrades to natural harmless substances.•The optical detector could distinguish between cleaned/uncleaned food conveyor belts.•The detector was fast and easily useable, e.g., for automated hygiene monitoring.
•Pilot-plant scale salad-rinsing unit based on plasma technology.•Plasma processed water as ‘on demand’ antimicrobial agent based on non-thermal atmospheric pressure plasma technology.•During the ...trial 45kg Endive (Cichorium endivia) and about 1.500l of plasma generated disinfectant were applied.•Enhancement of microbial reduction by nearly 2lg cycles in a single washing stage.•Advantages of PPW offer a wide range of possible uses for sanitation in food industry.
The increasing demands of society for healthy nutrition in combination with continuously decreasing willingness to spend time for food preparation leads to a rising consumer demand for minimal processed ready-to-eat (RTE) products (convenient food).
The USA is the leading nation in the consumption and therefore, the biggest market for these kinds of products. Thus, the U.S. Food and Drug Administration (FDA) has long term experience in the evaluation of consequences of the consumption of minimal processed RTE products. This authority publicized a list of the ten riskiest foods with leafy greens on the top.
Sanitation steps based on plasma processes could be an promising addition to conventional cleaning procedures. Plasma, often introduced as forth state of matter, differs from the gaseous state of matter by a certain amount of free charge carriers caused by ionization processes of the gas atoms and molecules due to the supply of energy. The electrical conductivity allows supplying the energy needed to sustain this state electrically, giving access to a huge variety of plasma generation methods with excitation frequencies from DC to several GHz offering wide parameter ranges e.g. electron energies from 0.5eV to 10eV.
The treatment of natural products with changing parameters like size, shape or water content is a challenging task for design and optimization of plasma processes. The lack of effectiveness of sanitation processes on the surfaces of food products is a general problem of all discussed methods.
In order to overcome these problems a specific plasma process was established, based on a microwave plasma torch operated with compressed air delivering plasma processed air (PPA) as antimicrobial acting process gas. If PPA is brought into contact with water, plasma processed water (PPW) is generated which has antimicrobial properties. This PPW process was implemented into a pilot-plant scale salad-rinsing unit in order to demonstrate the scalability and applicability of this treatment procedure. During the trial 45kg Endive (Cichorium endivia) and about 1.500l of plasma generated disinfectant were consumed. Off the cuff, the process was competitive to industrial established chemical processes.
Currently used methods for decontamination and sanitation of fresh/fresh‐cut food as well as food processing surfaces are antimicrobial ineffective, generate high costs with a high consumption of ...water, and chemicals additionally. As an alternative, non‐thermal plasma at atmospheric pressure could be a versatile tool. Therefore, an experimental set‐up based on a microwave‐plasma source which generates plasma processed air (PPA) containing manifold RNS‐based chemical and antimicrobial compounds is used. The PPA is introduced into a reaction chamber for the decontamination of packaging material and fresh produce. This is a new and innovative method for the generation of antimicrobial active air used for dry sanitation. In our experiments, PET stripes, fresh‐cut lettuce, and fresh sprouts are contaminated with six different bacteria; Escherichia coli K12 (DSM 11250), Pseudomonas fluorescens (DSM 50090), Pseudomonas fluorescens (RIPAC), Pseudomonas marginalis (DSM 13124), Pectobacterium carotovorum (DSM 30168), and Listeria innocua (DSM 20649) in a concentration of 108 cfu ml−1 and subsequently treated with PPA. For PPA production, the plasma is ignited for 5, 15, or 50 s. After a post‐plasma treatment with PPA of maximum 5 min, decreases of bacterial load up to 6 log10 cfu ml−1 are detected for P. fluorescens (both strains) and P. carotovorum on PET. On plant tissue only once a reduction higher than 5 log10 cfu ml−1 is gained (P. carotovorum on sprouts). For all other bacteria and specimen, the inactivation rate is less. The characteristics of plasma and its generated cocktail of long living chemical compounds in air leading to a high bacterial inactivation and offering a wide range of possible applications.
An experimental set‐up based on microwave discharge generates plasma processed air (PPA) containing RNS‐based antimicrobial compounds. PPA is used for sanitation of PET, fresh‐cut salad, and fresh sprouts. Plasma ignition is in time range of seconds and postplasma treatment of maximum 5 min. Bacterial load decreases up to 6 log10 cfu ml−1. Components of PPA are leading to a high bacterial inactivation and offering a wide range of possible applications.
In the European Union, foodborne outbreaks caused by Salmonella Enteritidis, related to eggs and egg products, have even been reported in 2018. Atmospheric pressure plasma is becoming increasingly ...important as a decontamination method. A semidirect cold atmospheric pressure plasma, the flexible electrode plasma source, was developed for treating whole hen's eggs. An average reduction of 1.16 and 0.95 log colony‐forming units (CFU)/egg was achieved for the total bacterial count of clean and dirty eggs, respectively. An inactivation of 4.1 log CFU/egg Salmonella Enteritidis was achieved with artificially inoculated eggshells. Selected quality parameters and sensory properties were analysed. Overall, the present study yielded promising results for a realistic implementation of an industrial prototype plasma source.
A semidirect flexible electrode plasma source was tested as a new decontamination method for whole hen's eggs. The effective inactivation of artificial Salmonella Enteritidis contamination was realised, and no influence on selected quality parameters could be detected. Slight variances were revealed by the first‐time sensory testing, thus requiring further optimisation of the plasma source.
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