Plasma-activated Water Research Articles

Synergistic Effect of Plasma-Activated Water with Micro/Nanobubbles, Ultraviolet Photolysis, and Ultrasonication on Enhanced Escherichia coli Inactivation in Chicken Meat

The use of integrated plasma-activated water (PAW) with micro/nanobubbles (MNBs), ultraviolet (UV) photolysis, and ultrasonication (US) for the synergistic efficiency of Escherichia coli inactivation in chicken meat was investigated. A 2k factorial design was employed to optimize the combined treatment parameters for pathogen disinfection in Design of Experiments (DOE) techniques. Its effectiveness was evaluated based on electrical conductivity (EC), oxidation–reduction potential (ORP), hydrogen peroxide (H2O2) concentration, and E. coli inactivation. The most significant impact on E. coli reduction was observed for MNBs, UV treatment time, and their interaction (MNBs and UV). Optimal E. coli inactivation (6 log10 CFU/mL reduction) was achieved by combining PAW with MNB and UV for 10 and 20 min, respectively. Integrating PAW with appropriate supplementary technologies enhanced E. coli inactivation by 97% compared to PAW alone. This novel approach provides a promising alternative for pathogen control in chicken meat, potentially improving food safety and shelf life in the poultry industry.

Plasma-activated water in combination with coconut exocarp flavonoids emerge as promising preservation technique for golden pompano: Impact of the treatment sequence

In the current study, the preservation effect of plasma-activated water (PAW), coconut exocarp flavonoids (CF) and their combination on golden pompano fillets during refrigerated storage was investigated with emphasize on the treating sequence. PAW effectively inactivated spoilage bacteria and inhibited total volatile basic nitrogen (TVB-N) increase, while boosted the TBARS and carbonyl values. PAW+CF exerted synergistic effect on extending the period before total bacterial count and TVB-N content reaching acceptance limit than PAW or CF alone (P < 0.05). In addition, their combined treatment effectively reduced fillets discoloration and texture deterioration. Simultaneously, lipid and protein oxidation were significantly inhibited, which was comparable to CF. It was indicated that the treatment sequence of PAW and CF profoundly impact the preservation effect. Specifically, prior CF marinating followed by PAW was more effective than the opposite sequence. Thus, combination of CF followed by PAW served as promising technique for fish fillets preservation.

Stable and efficient microbubble-enhanced cold plasma activation for treatment of flowing water

Cold plasma technology has received immense attention in several fields including wastewater treatment, disinfection, food processing and storage, and agriculture due to its ability to produce reactive species at low energy input. However, the scalability of generation of plasma activated water (PAW) still remains a challenge. A microbubble-enhanced cold plasma activation (MB-CPA) technology leverages small bubbles for effectively interfacing plasma discharge in a gas phase and a flow of liquid media. In this study, we develop a stable and efficient approach for the continuous production of PAW by maximizing the transfer of active species generated during plasma discharge to water flow. Novel Venturi-type microbubble generators were designed for the production of PAW by maximizing the rapid transfer of active species generated during plasma discharge in air. Key geometrical features of the tubes including the position and the opening size of the air inlet were tuned, aiming to transfer active species in a wide range of liquid flow conditions. The performance of our flow systems was evaluated by using pure water, buffered saline, and real river water containing micro-pollutants. We found that MB-CPA can effectively eliminate chemical compounds such as dye and antibiotic residues, as well as biological pathogens like Gram-positive and Gram-negative bacteria. In a cell viability assay, the technology exhibited cytotoxic effects against cancerous cells, specifically HeLa and MCF-07 cell lines. This multi-functionality underscores the versatility of MB-CPA, positioning it as a multifaceted solution for both water and wastewater treatment. Our work shows that the designed MB-CPA system represents a promising and sustainable technological advancement, offering a green alternative for the widespread activation of water in various applications.

Bactericidal efficacy of plasma-activated water against Vibrio parahaemolyticus on Litopenaeus vannamei.

In this study, the antimicrobial mechanism of plasma-activated water (PAW) against Vibrio parahaemolyticus and the effectiveness of PAW in artificially contaminated Litopenaeus vannamei were investigated. The results demonstrated a significant reduction (p < 0.05) in viable counts of V. parahaemolyticus with increasing plasma discharge time (5, 10, 20, and 30 min) and PAW immersion time (3, 5, 10, 20, and 30 s). Specifically, the count of V. parahaemolyticus decreased by 2.1, 2.7, 3.3, and 4.4 log CFU/mL after exposed to PAW 5, PAW 10, PAW 20, and PAW 30 for 30 s, respectively. Significant cell surface wrinkling, accompanied by notable nucleic acid and protein leakage were observed after treatment with PAW. The permeability of the inner and outer cell membranes was significantly increased (p < 0.05), along with an increase in electrical conductivity (p < 0.05). The reactive oxygen species (ROS) within V. parahaemolyticus cells were significantly increased (p < 0.05), while superoxide dismutase (SOD) activity, and the relative expression of the ompW, emrD, and luxS genes were significantly decreased (p < 0.05). A reduction number of 1.3, 1.8, 2.1, and 2.2 log CFU/g of V. parahaemolyticus in artificially contaminated L. vannamei was obtained with PAW for 5 min. The study elucidated that PAW could destroy cell membranes, leading to cell death. The findings would strengthen strategies for V. parahaemolyticus control and provide a potential application of PAW for preserving aquatic products.

Effect of Sequential Treatment of Plasma Activated Water and Bacteriophage on Decontamination of Salmonella Typhimurium in Lettuce

Ensuring food safety measures are essential to minimize the risk of foodborne diseases linked to raw food products. Here, we investigated the efficacy of an innovative approach for the control of Salmonella Typhimurium found in fresh produces. Plasma activated water (PAW) and bacteriophages are emerging effective and valuable alternative methods for microbiological decontamination. The efficacy of PAW and a lytic bacteriophage (109 PFU/mL), both separately and sequentially, against S. Typhimurium in fresh produce was investigated. S. Typhimurium (105–107 CFU/g) were inoculated on lettuce leaves and treated with PAW, S. Typhimurium phage SK-T2 or their combination. PAW or bacteriophage inactivated S. Typhimurium, on lettuce leaves at different initial populations, by 2.90–3.46 or 1.45–3.25 log CFU/g, respectively. After sequential treatments of PAW and bacteriophage, S. Typhimurium populations, initially applied at ~ 105 CFU/g reduced by 4.47 log CFU/g, but when the order of application was changed (i.e., bacteriophage followed by PAW), the combination synergistically decreased the Salmonella numbers below the detection limit of the method used for the enumeration (i.e., < 101 CFU/g). At the high-level inoculum (~ 7 log CFU/g), consecutive treatments of PAW and phage decreased the S. Typhimurium population by 3.28 log CFU/g, and a reduction of 6.20 log CFU/g was achieved after reversing the order of treatment. Regardless of the bacterial inoculum level, sequential applications of bacteriophage and PAW resulted in a higher level of inactivation. This study proved that the bacteriophage–PAW combination constitutes a promising alternative approach to the conventional washing process in fresh produce wash waters in the food industry.Graphical

Production of large quantity of plasma activated water using multiple plasma device setup

This study focuses on large-scale production of plasma-activated water (PAW) using batch processes with circulating and non-circulating modes. A multi-plasma device setup, powered by a self-developed high-voltage high-frequency supply. This plasma is electrically characterized and the produced radicals/species are identified using emission spectroscopy, with resulting effluent gases containing polluting species. The PAW setup utilizes these gases to create substantial quantities of PAW, decreasing environmental pollutants. The non-circulating mode produces highly reactive PAW (2L/batch) while the circulating mode yields larger volumes (20L/batch) with lower reactivity. Applications range from microbial inactivation to agriculture. Both batch setups are scalable for industrial PAW production.

The Influence of Voltage on Gliding Arc Discharge Characteristics, the Composition of Air Plasma, and the Properties of BG-11 Medium

A gliding arc discharge (GAD) plasma device has been developed and tested. Possible applications areas for GAD plasma could be microalgae suspension treatments and the creation of plasma-activated water. To understand its behavior, the influence of the input power on the electrical characteristics of the generated GAD plasma was investigated using an oscilloscope. The waveforms of the voltage and current of GAD plasma are presented. The duration of the discharge time and the evolution of the arc during discharge were determined and investigated. It was revealed that the increase in the output voltage prolonged the duration of the arc discharge. The composition of the air plasma was investigated using a flame-emission spectrometer and acousto-optic emission spectrometer. It was revealed that the main species in the emission spectra of the GAD air plasma were N2, N2+, N+, NO, and O species. Furthermore, the increase in the input power enhanced the ionization degree of the air plasma and increased the intensities of the emission lines associated with N2+, NO, and O species. An increase in the conductivity of the BG-11 medium was observed. Physicochemical analyses of the plasma-activated BG-11 medium indicated an increase in the concentration of nitrite and nitrate ions and hydrogen peroxide with an enhancement of the voltage.

Effect of Plasma-Activated Water (PAW) on the Postharvest Quality of Shepherd's Purse (Capsella bursa-pastoris).

Plasma-activated water (PAW) treatment is an effective technique for the quality retention of fresh vegetables with cold atmospheric plasma using controllable parameters. This study investigated the effect of PAW on the postharvest quality of shepherd's purse (Capsella bursa-pastoris). The results displayed that PAW treatment with an activation time of 5, 10, 15, and 20 min reduced the yellowing rate and weight loss of the shepherd's purse during 9 days of storage. Compared with untreated samples, PAW treatment at different times reduced the number of total bacteria, coliform, yeast, and mold by 0.18-0.94, 0.59-0.97, 0.90-1.18, and 1.03-1.17 Log CFU/g after 9 days of storage, respectively. Additionally, the treatments with PAW-5 and PAW-10 better preserved ascorbic acid, chlorophyll, total phenol, and total flavonoid contents. They also maintained the higher antioxidant and CAT activity and inhibited the formation of terpenes, alcohols, and nitrogen oxide compounds of the shepherd's purse at the end of storage. The microstructural result illustrated that the cells of the shepherd's purse treated with PAW-5 and PAW-10 were relatively intact, with a small intercellular space after storage. This study demonstrated that PAW treatment effectively improved the postharvest quality of shepherd's purse.

Seed priming with gas plasma-activated water in Ethiopia’s “orphan” crop tef (Eragrostis tef)

Main conclusionSeed priming with gas plasma-activated water results in an increased ageing resilience in Eragrostis tef grains compared to a conventional hydropriming protocol.Tef (Eragrostis tef) is a cereal grass and a major staple crop of Ethiopia and Eritrea. Despite its significant importance in terms of production, consumption, and cash crop value, tef has been understudied and its productivity is low. In this study, tef grains have undergone different priming treatments to enhance seed vigour and seedling performance. A conventional hydropriming and a novel additive priming technology with gas plasma-activated water (GPAW) have been used and tef grains were then subjected to germination performance assays and accelerated ageing. Tef priming increases the germination speed and vigour of the grains. Priming with GPAW retained the seed storage potential after ageing, therefore, presenting an innovative environmental-friendly seed technology with the prospect to address variable weather conditions and ultimately food insecurity. Seed technology opens new possibilities to increase productivity of tef crop farming to achieve a secure and resilient tef food system and economic growth in Ethiopia by sustainable intensification of agriculture beyond breeding.

Implementing water recirculation in a novel portable plasma-activated water reactor enhances antimicrobial effect against Escherichia coli

The need for sustainable and reliable decontamination methods is driven by concerns regarding antibiotic resistance, as well as environmental and cost-efficiency challenges associated with traditional methods. Plasma-activated water (PAW) holds significant promise as an innovative and eco-friendly decontamination method. Nevertheless, prior to industrial implementation of PAW-based decontamination devices, a deep understanding of the bacterial inactivation mechanisms and its interplay with PAW chemical composition is required. Advancing in this field requires interdisciplinary and collaborative research using standardized practices with cost-effective and shareable PAW reactors that are still missing today. Here, to this end, a portable PAW reactor, featuring a surface dielectric barrier discharge (SDBD) that operates in air, is presented. The gaseous and aqueous phases were chemically characterized by Fourier transform infrared (FTIR) absorption spectroscopy and vis-spectrophotometry, respectively. To assess PAW antimicrobial efficacy Escherichia coli was employed as a model organism on six different PAW samples for three different treatment times. The significance of water recirculation in controlling the chemical composition of PAW, altering the nitrogen species balance in favor of NO2−, is demonstrated. This chemical modification consequently enhanced the antimicrobial effectiveness of PAW, reaching a log reduction of ∼6. Exposing E. coli to equivalent concentrations of RONS to those found in PAW attained similar log-reductions, indicating that acidified nitrites are key to PAW antimicrobial activity. Through an innovative and portable design, this study illustrates the crucial role of water recirculation in tailoring PAW composition, leading to improved decontamination capabilities and establishing a key parameter for further optimization of PAW production.

Iron nanoparticle coating and plasma-activated water cleaning as a biofouling removal method for reverse osmosis membranes suitable for desalination

Desalination provides crucial freshwater, but biofouling on reverse osmosis (RO) membranes is a major challenge due to hard-to-remove biofilms. Conventional treatments are often ineffective, prompting a shift to coatings with nanoparticles like copper, silver, and iron to combat fouling. This study demonstrates a unique combination of coating RO membranes with iron nanoparticles (FeNPs) and treatment with plasma-activated water (PAW) for the removal of biofilm formation. Pure and unbound FeNPs showed no significant inhibition of Escherichia coli biofilms. However, the attachment of FeNPs to RO membranes led to a decrease in biofilm growth on the membrane, and an additional PAW treatment was shown to significantly inhibit mature biofilms. SEM imaging revealed a higher density and uniform distribution of FeNPs on the RO membranes after PAW treatment. Zeta potential measurements showed positively charged FeNPs in PAW, enhancing their attraction with the negative membrane surfaces. The coated membrane using PAW solution with FeNPs exhibited no degradation in terms of pure water flux, saline water flux, and salt rejection compared to the immersion process in DI with FeNPs.

Falling liquid droplets discharge

This paper reports the phenomenon of two plasma segments forming when a water droplet descends, one between the upper part of the droplet and the outlet tube and the other between the lower part of the droplet and the water surface in the container. The study reveals that as the water droplet descends, the length of the upper plasma gradually increases, while the length of the lower plasma decreases until the lower plasma disappears upon contact between the water droplet and the water in the container. The study finds that the rotational temperature of this plasma reaches 2100 K, with an electron density of 1014 cm−3. Furthermore, it is intriguing to note that the descent speed of the droplet is significantly greater than that of a freely falling droplet. Further research indicates that this is due to an instant water channel explosion-induced downward impact on the droplet caused by plasma generation at the upper part of the droplet. The advantage of this device lies in the fact that the plasma only comes into direct contact with water, without any contact with metal electrodes, thus eliminating the issue of electrode corrosion. Furthermore, since the water is in dynamic flow, it facilitates the dissolution of reactive gaseous components into the water, making it suitable for applications related to plasma-activated water and similar purposes.

Chlorpyrifos Pesticide Removal from Black Grapes Using Plasma-Activated Water Produced by Plasma Bubbling Technology

This study is aimed at evaluating the ability of plasma-activated water (PAW) to reduce the chlorpyrifos pesticide residue in black grapes. Raw black grapes were spiked with a known concentration (10, 15, and 20 ppm) of chlorpyrifos (20% EC) and bubbled with 120 V air plasma at three different time intervals (5, 10, and 15 min). GC-MS analysis of these plasma-bubbled grapes showed up to 65.25% reduction (20 ppm sample) in chlorpyrifos content after 15 min of treatment. However, the treatment also reduced the grape juice’s ascorbic acid (19.97±2.69 to 9.15±2.02 mg/ml), antioxidant scavenging activity (77.42±2.97 to 53.30±4.77%), total flavonoids (3.00±0.53 to 2.61±0.57 mg QE/ml), total soluble solids (14.23±1.96 to 11.95±1.86°), total suspended solids (1.95±0.16 to 1.80±0.03 g/l), and turbidity (246.63±11.42 to 224.1±24.85 NTU). Meanwhile, other physicochemical attributes such as pH, titrable acidity, total phenol content, color index, and texture values had slight changes after plasma bubbling. Thus, plasma bubbling proved to be an effective method to remove the chlorpyrifos pesticide present in grapes, and the techniques also preserve the quality of the commodity.

Combined of plasma-activated water and dielectric barrier discharge atmospheric cold plasma treatment improves the characteristic flavor of Asian sea bass (Lates calcarifer) through facilitating lipid oxidation

To explore the combination effects of plasma-activated water and dielectric barrier discharge (PAW-DBD) cold plasma treatment on the formation of volatile flavor and lipid oxidation in Asian sea bass (ASB), the volatile flavor compounds and lipid profiles were characterized by gas chromatography-ion mobility spectrometry and LC-MS-based lipidomics analyses. In total, 38 volatile flavor compound types were identified, and the PAW-DBD group showed the most kinds of volatile components with a significant (p < 0.05) higher content in aldehydes, ketones, and alcohols. A total of 1500 lipids was detected in lipidomics analysis, phosphatidylcholine was the most followed by triglyceride. The total saturated fatty acids content in PAW-DBD group increased by 105.02 μg/g, while the total content of unsaturated fatty acids decreased by 275.36 μg/g. It can be concluded that the PAW-DBD processing increased both the types and amounts of the volatile flavor in ASB and promoted lipid oxidation by altering lipid profiles.

Atmospheric non-thermal plasma inactivation of Ascosphaera apis, the causative agent of chalkbrood disease in honeybee

Ascosphaera apis is a worldwide pathogenic fungi of honeybees that can cause a decline in bee populations. In this study, we investigated the antifungal activity of non-thermal plasma on fungal growth. Spore inactivation after exposure to gas plasma by liquid phase and plasma activated water (PAW) and pathogenicity of A. apis in vivo were also examined. The results demonstrated that the mycelial growth of fungi was completely inhibited after argon plasma treatment. Both gas plasma and PAW exposures resulted in a significant decrease of A. apis spore numbers, maximum reduction of 1.71 and 3.18-fold, respectively. Germinated fungal spores on potato dextrose agar were also reduced after plasma treatment. SEM analysis revealed a disruption in the morphological structure of the fungal spores. The pathogenicity of A. apis on honeybee larvae was decreased after spores treated by gas plasma and PAW with a disease inhibition of 63.61 ± 7.28% and 58.27 ± 5.87%, respectively after 7 days of cultivation. Chalkbrood in honey bees have limited control options and our findings are encouraging. Here, we demonstrate a possible alternative control method using non-thermal plasma for chalkbrood disease in honeybees.

Effect of cold plasma treatment and plasma‐activated water on physicochemical and structural properties of starch: A green and novel approach for environmental sustainability

AbstractStarch is a crucial part of the human dietary regimen. Still, its restricted water solubility, low viscosity, and weak heat stability are unfavorable physicochemical characteristics that restrict its use in food applications. So, in the 21st century, green and novel technologies such as cold plasma technology (CPT) and plasma‐activated water (PAW) have been employed for starch modification to improve the starch's physicochemical, digestibility, functional, structural, and thermal properties. This article provided an in‐depth evaluation of the use of cold plasma intervention in starch systems. Moreover, starch was modified due to cross‐linking, plasma etching, and depolymerization mechanisms mediated by plasma species. We may conclude that CPT and PAW are substitute methods for changing starch characteristics.

Development of Plasma-Activated Water (PAW) System: Molecular Dynamics Simulation and Experimental Study on Almond Aflatoxins

Almonds play a significant role in Iran’s economy, and factors that threaten their market, such as aflatoxins, need careful consideration. Plasma-activated water (PAW) is a new method that has antioxidant activity and can eliminate toxins and microbial agents, making it a suitable solution for removing aflatoxins from almonds. In a study, the continuous PAW production system was used to control and remove almond aflatoxins, and molecular dynamics simulation was employed to evaluate the impact of PAW on aflatoxin B1. The study found that reducing the flow rate of plasma-treated water had the greatest effect on reducing aflatoxin concentration, followed by PAW application time, the dose of inoculated toxin, and the air/gas mixture ratio. The use of PAW reduced aflatoxin concentration in almonds by 12% to 56.8%. The simulation results suggested that PAW can affect the structure of aflatoxin B1, change and destroy its activity, and reduce its toxicity. Among the free radicals tested, NO3− was found to be the most effective in degrading aflatoxin B1. This study demonstrates the potential of PAW as a method to remove aflatoxins and enhance the safety of almonds.

Disinfection Efficacy of Electrohydraulic Discharge Plasma against Xanthomonas campestris pv campestris: A Sustainable Seed Treatment Approach.

The prevalence of plant diseases caused by pathogens such as Xanthomonas campestris pv campestris (Xcc) poses a significant challenge to sustainable agriculture, necessitating the development of effective and eco-friendly disinfection methods. In this study, we investigated the efficacy of electrohydraulic discharge plasma (EHDP) as a promising alternative for disinfection against Xcc, a pathogen responsible for black rot in cruciferous vegetables. Unlike conventional gas-phase plasma, EHDP introduces two pivotal components: gas-liquid interface plasma (GLIP) and its consequential byproduct, plasma-activated water (PAW). While GLIP enables dual-phase production of reactive oxygen and nitrogen species (RONS), PAW is a reservoir of liquid-phase long-lived RONS, thereby enhancing its bactericidal efficacy. In our evaluations, we tested EHDP-induced GLIP and EHDP-induced PAW against Xcc cells in both in vitro (Xcc suspension) and in vivo (Xcc-inoculated cabbage seeds) settings, achieving noteworthy results. Within 15 min, these methods eliminated ∼98% of the Xcc cells in suspension. For in vivo assessments, nontreated seeds exhibited an infection rate of 98%. In contrast, both EHDP treatments showed a significant reduction, with ∼60% fewer seeds infected while maintaining ∼90% germination rate. In addition, the liquid-phase RONS in EHDP-PAW may enhance seed vigor with a faster germination rate within the initial 5 days. Remarkably, around 90% of EHDP-PAW-treated seeds yielded healthy seedlings, indicating dual benefits in bacterial suppression and seed growth stimulation. In contrast, the percentage of healthy seedlings from nontreated, Xcc-inoculated seeds was approximately 70%. Our research demonstrates the feasibility of using eco-friendly EHDP in the seed disinfection process.

Study on the thawing characteristics of beef in plasma-activated water

Plasma-activated water (PAW) thawing and traditional water thawing were used to study the thawing characteristics and physicochemical properties of beef, and infrared spectroscopy, scanning electron microscopy and other technologies were used as detection methods. The activation times of plasma-activated water (PAW) were 20, 40, 60, 80 and 100 min, respectively. The results showed that, compared with traditional water thawing, the PAW thawing treatment could reduce the total number of bacteria in the meat by 0.5 log, and the medium itself had a more significant bactericidal effect of up to 1.7–2.6 log, and had no adverse effect on the color or pH of the beef. Moreover, PAW maintained the stability of beef fiber, improved the water-holding capacity, inhibited lipid oxidation, and reduced the loss of soluble substances such as proteins. Therefore, PAW thawing is a promising beef thawing technology that provides practical guidance and methods for the wider application of PAW in the field of beef thawing. Industrial relevanceThe thawing characteristics and physicochemical properties of beef by plasma-activated water (PAW) were investigated. It was found that PAW had a positive effect on decontamination bacteria, improving the water-holding capacity of beef, inhibiting lipid oxidation and maintaining the fiber structure of beef. The potential application of PAW in the thawing of frozen meat products was highlighted.

Cold plasma treatment boosts barley germination and seedling vigor: Insights into soluble sugar, starch, and protein modifications

This study investigates the impact of three cold plasma treatments on barley seed germination: direct treatment of dry seeds (DDS), direct treatment of water-soaked seeds (DWS), and indirect treatment of seeds using plasma-activated water (IPAW). Our findings reveal that while DDS maintained the seed's imbibition structures, DWS significantly reduced water uptake. Notably, DWS-treated seeds exhibited a substantial increase in moisture content, potentially leading to an oxygen-deficient environment within the seed. This condition appeared to hinder germination, contrasting with the beneficial effects observed in DDS-treated seeds. Analyses of surface hydrophilicity, phenolic compounds, carbohydrate composition, protein storage and seedling growth were conducted. Interestingly, cold plasma treatment enhanced seed surface hydrophilicity, as evidenced by a decrease in water contact angles, particularly for DWS. We observed specific reductions in flavonoids and total phenolics, alongside shifts in carbohydrate composition, including increased sugar content up to 15.1% (DDS) and 13.5% (DWS), accompanied by a decrease in starch content to 189.00 ± 7.86 mg/g FM for DWS. Protein storage assessments revealed declines in albumin, globulin and prolamin fractions post-CP exposure. Finally, DDS and IPAW treatments markedly improved seedling shoot growth (from two to three-fold), underscoring the potential of these treatments in enhancing barley germination.