Physicochemical Properties Of Plasma-activated Water Research Articles

Comparison of the Bacterial Inactivation Efficiency of Water Activated by a Plasma Jet Source and a Pin-to-Pin Electrode Configuration Source

In this comparative study, the bacterial inactivation efficiency of plasma-activated water (PAW) generated by two distinct plasma reactors, one utilizing a nitrogen plasma jet electrode and the other a hybrid argon plasma reactor, was explored. The present study involved the assessment of antimicrobial activity against suspensions of three Gram-positive and three Gram-negative bacterial strains in their planktonic cell state. Bacterial suspensions were introduced into PAW five days after generation. Subsequently, the viability of the bacteria was assessed at various time intervals, specifically at 0.5, 1, 3, 5, 10, and 24 h, in order to evaluate the effect of inactivation. Structural changes in bacteria after PAW treatment were assessed using a scanning electron microscope (SEM). The physicochemical properties of PAW, including pH, conductivity, and concentrations of H2O2, NO2−, and NO3− during aging were measured. The present study demonstrated the effective inactivation of the tested bacterial strains by PAW. Gram-positive bacteria displayed greater resistance compared to Gram-negative species, with the lowest reductions in bacterial counts observed for B. cereus, and the highest for Escherichia coli O157:H7. Morphological damage was evident across all bacterial species examined. Physicochemical measurements showed slow decay of the reactive species in the aging process. This study illustrated the potential utility of PAW as an alternative disinfectant.

Effect of different process conditions on the physicochemical and antimicrobial properties of plasma-activated water

The physicochemical properties of plasma-activated water (PAW) generated under different process conditions were investigated, and their changes under different storage conditions were also studied. The results showed that increasing the processing time and power, and decreasing generated water volume, could cause an increase in the redox potential, conductivity, and temperature of PAW, and a decrease in its pH. A slower dissipation of the reactive oxygen and nitrogen species in PAW was found on storage at 4 °C in a sealed conical flask than on storage at room temperature. The inactivation ability of plasma-activated lactic acid (LA) to Listeria monocytogenes (L. monocytogenes) and Pseudomonas aeruginosa (P. aeruginosa) was higher than that of PAW or LA alone under the same experimental conditions. The results of this study may provide theoretical information for the application of PAW as a potential antimicrobial agent in the future.

Potential use of plasma‐activated water on Escherichia coli for sterilization: Efficacy and mechanism

AbstractThe plasma‐activated water (PAW) produced by low‐temperature plasma (LTP) was applied to this research because of its safety and no thermal damage. Therefore, the physicochemical properties of PAW, as well as the efficacy and sterilization mechanism of Escherichia coli, were discussed. The PAW (pH 1.27, conductivity 6400 μS/cm) could reduce E. coli by 1.31‐log reduction using LTP at 70 W for 9 min. The results demonstrated that PAW caused DNA and protein leakage with malondialdehyde production. This study may provide a basis for the theoretical research of PAW sterilization. As an effective sterilant, PAW would be a promising alternative strategy for cleaning of E. coli from pipes and filters in food factories.

Effects of heating on the antibacterial efficacy and physicochemical properties of plasma-activated water

Plasma-activated water (PAW), which is the water treated by cold plasma, represents a promising strategy for food decontamination. However, studies of the influences of heating on the antibacterial efficacy and physicochemical characteristics of PAW are limited. Therefore, the present work is aimed at determining the effect of heating on the bactericidal effects and physicochemical properties of PAW. PAW (1.0 mL) was heated in a water bath at 30–80°C for 10 min. After being cooled to room temperature, the antibacterial efficacy and physicochemical properties of PAW were measured. Heating at 40–80°C for 10 min caused a significant decrease in the antibac-terial activity of PAW against Listeria monocytogenes and Salmonella typhimurium. After heating at 40–80°C for 10 min, the pH value and oxidation reduction potential (ORP) of PAW remained stable, and the level of nitrate and electrical conductivity of PAW remarkably increased, while hydrogen peroxide and nitrite contents significantly decreased. The combination treatment of PAW and mild heating (40–60°C for 4 min) showed greater anti-bacterial effect on L. monocytogenes and S. typhimurium. After the combined treatment of PAW with mild heating at 60°C for 4 min, the populations of L. monocytogenes and S. typhimurium decreased by 7.83 log10 CFU/mL and 9.35 log10 CFU/mL, respectively, which were significantly higher than that caused by PAW at 25°C or mild heating at 60°C alone. In summary, the antibacterial activity of PAW is significantly affected by the treatment temperature. This work provides a basis for the practical application of PAW in the food industry.

Physicochemical Properties of Plasma-Activated Water and Its Control Effects on the Quality of Strawberries

In this study, the effects of plasma-activated water (PAW), generated by dielectric barrier discharge cold plasma at the gas-liquid interface, on the quality of fresh strawberries during storage were investigated. The results showed that, with the prolongation of plasma treatment time, the pH of PAW declined dramatically and the electrical conductivity increased significantly. The active components, including NO2-, NO3-, H2O2, and O2-, accumulated gradually in PAW, whereas the concentration of O2- decreased gradually with the treatment time after 2 min. No significant changes were found in pH, firmness, color, total soluble solids, malondialdehyde, vitamin C, or antioxidant activity in the PAW-treated strawberries (p > 0.05). Furthermore, the PAW treatment delayed the quality deterioration of strawberries and extended their shelf life. Principal component analysis and hierarchical cluster analysis showed that the PAW 2 treatment group demonstrated the best prolonged freshness effect, with the highest firmness, total soluble solids, vitamin C, and DPPH radical scavenging activity, and the lowest malondialdehyde and ∆E* values, after 4 days of storage. It was concluded that PAW showed great potential for maintaining the quality of fresh fruits and extending their shelf life.

Effect of Plasma activated water (PAW) on physicochemical and functional properties of foods

Plasma activated water (PAW) is an advanced technology that has gained intensive attention being protecting the food products from physical, chemical, and biological contaminations. The generated reactive oxygen species (ROS) and reactive nitrogen species (RNS) during process are the main reasons for preservation of food products. By applying PAW, the unprocessed and processed food products are kept safe from microbes during storage periods, however the quality is affected. The reaction between ROS/RNS with constituents of food materials leads to changes in texture, structure, physiochemical and nutritional properties. Although the various application of PAW in the food industry such as decontamination of microbes, thawing of food, curing of meat products, and combined effect with other technologies have been extensively evaluated, but a complete analysis of the effect of PAW on the quality of food is somehow lacking. In this context, the present review focuses on the impact of PAW application on chemical, nutritional, and textural changes in food. Further, the effect of processing parameters of PAW on the modification of food constituents and sensory attributes are described in detail. In addition, the physicochemical properties of PAW after being produced by several modes are also reviewed. Finally, this review also highlights several limitations of PAW treatment and suggests further research directions of the technology. •Plasma activated water (PAW) is considered as GRAS for food decontamination. • Generated reactive species from PAW could be the superior preservatives than CP. •Physicochemical properties and parameters of PAW effect on the food quality. •The reactive species interact with food constituents during or after treatment. •The nutritional, functional, structural and sensory changes are seen in food products.

Nitrox surface discharge used for water activation: the reactive species and their correlation to the bactericidal effect

Plasma activated water (PAW) is a promising green antibacterial agent and the bactericidal effect is complicatedly affected by electron bombardment, ultraviolet radiation, interface reaction, and cascade chemical reaction. In this paper, a case of preparing PAW by treating aqueous solutions with afterglow gas is constructed based on surface micro-discharge (SMD), which focuses on the effect of afterglow gas–liquid mass transfer and liquid phase chemistry on PAW sterilization. The correlation of the bactericidal effect of PAW to the reactive species was studied based on the model of methicillin-resistant Staphylococcus aureus. The production of reactive oxygen and nitrogen species (RONS) in PAW with the regulation of N2/O2 ratios in the working gas for SMD. The RONS in both gas and liquid phases and the physicochemical properties of PAW were measured through optical and chemical methods. In addition, the effects of liquid types, liquid conductivity, and storage time on the bactericidal effects of PAW were explored. The key species for bacteria inactivation were identified by equivalent mixed solutions and specific scavengers. The results demonstrated that control of the N2/O2 ratios in the working gas can effectively improve the RONS in plasma and PAW. The bactericidal effect of PAW is correlated with peroxynitrite, superoxide anion, and their synergistic effects in an acidic liquid environment. This study provides a new strategy for insight into the bactericidal mechanism of PAW in biomedical applications.

Combined effects of ultrasound, plasma-activated water, and peracetic acid on decontamination of mackerel fillets

It is usually quite challenging to rely on one single intervention to achieve a satisfactory antimicrobial effect and maintain quality attributes of food. This study aimed to investigate the decontamination effectiveness of individual treatments, including ultrasound (US), plasma-activated water (PAW), and peracetic acid (PAA) and their combinations against native microbiota (total mesophilic bacteria (TMC) and total psychrotrophic bacteria (TPC)) and inoculated bacteria (Escherichia coli, Listeria innocua, and Pseudomonas fluorescens) on raw mackerel fillets. The impacts of the treatments on fish quality characteristics, such as colour, and lipid oxidation (primary and secondary products) were determined. Meanwhile, the physicochemical properties of PAW and plasma-activated PAA (PA-PAA), including pH, oxidation-reduction potential (ORP), conductivity, and reactive oxygen nitrogen species (RONS) after plasma treatment were examined. The results showed that combined treatments involving PAA tended to achieve higher inactivation rates, with the greatest inactivation of 0.72, 0.62, and 0.5 log CFU/g for L. innocua, E. coli, and P. fluorescens respectively. Significantly higher values of RONS and more acidic pH in PA-PAA were observed than that in PAW or PAA (P ≤ 0.05), demonstrating the synergistic effect of the hurdle interventions, though the inactivation rates on the fish samples were not significantly higher than the individual treatments. Fish quality parameters were not notably affected compared to the control. The study showed promising results for fish decontamination, offering potential alternative options for future application.

Plasma-activated water: Physicochemical properties, microbial inactivation mechanisms, factors influencing antimicrobial effectiveness, and applications in the food industry.

Novel nonthermal inactivation technologies have been increasingly popular over the traditional thermal food processing methods due to their capacity in maintaining microbial safety and other quality parameters. Plasma-activated water (PAW) is a cutting-edge technology developed around a decade ago, and it has attracted considerable attention as a potential washing disinfectant. This review aims to offer an overview of the fundamentals and potential applications of PAW in the agri-food sector. A detailed description of the interactions between plasma and water can help to have a better understanding of PAW, hence the physicochemical properties of PAW are discussed. Further, this review elucidates the complex inactivation mechanisms of PAW, including oxidative stress and physical effect. In particular, the influencing factors on inactivation efficacy of PAW, including processing factors, characteristics of microorganisms, and background environment of water are extensively described. Finally, the potential applications of PAW in the food industry, such as surface decontamination for various food products, including fruits and vegetables, meat and seafood, and also the treatment on quality parameters are presented. Apart from decontamination, the applications of PAW for seed germination and plant growth, as well as meat curing are also summarized. In the end, the challenges and limitations of PAW for scale-up implementation, and future research efforts are also discussed. This review demonstrates that PAW has the potential to be successfully used in the food industry.

Inactivation efficacy of plasma‐activated water: influence of plasma treatment time, exposure time and bacterial species

SummaryThis study aimed to evaluate the influence of plasma treatment time, bacterial exposure time to PAW and bacterial species on the inactivation efficacy of plasma‐activated water (PAW), with additional investigation of the inactivation mechanisms of PAW. Six bacterial species, including Listeria innocua, Staphyloccus aureus, Escherichia coli, Pseudomonas fluorescens, Shewanella putrefaciens and Aeromonas hydrophila were selected as the representative bacteria. The initial bacterial concentration was around 7 log CFU ml−1 after mixing with PAW, and the inactivation efficacy was measured after different exposure times during the 4 °C storage. Scanning electron microscopy (SEM) images of the bacteria after PAW treatment were carried out to inspect the cell structure damage, and physicochemical properties of PAW, including pH, conductivity and long‐living reactive species of H2O2, , and , were examined. The results showed that the inactivation efficacy of PAW was positively correlated with plasma treatment time and bacterial exposure time, and for the species examined in this study, the Gram‐negative species were more sensitive to PAW than the Gram‐positive species. Cell structure damage, including shrinkage, distortion, or holes, was observed after PAW treatment. The pH of PAW was acidified to 2.5–2.9, and conductivity was significantly increased to 518.0 μs cm−1. and H2O2 were reduced during the 48 h storage, while an increased concentration was observed for . This study demonstrated that the processing parameters of plasma treatment time, exposure time and characteristics of bacteria can significantly affect the inactivation efficacy of PAW.

Inactivation efficacy and mechanisms of plasma activated water on bacteria in planktonic state.

The study aimed to investigate the inactivation efficacy and mechanisms of plasma activated water (PAW) on selected bacteria in planktonic state. Plasma activated water was generated using an atmospheric cold plasma jet at 15, 22 and 30kV for 5min. Escherichia coli, Listeria innocua, Staphylococcus aureus, Aeromonas hydrophila, Pseudomonas fluorescens and Shewanella putrefaciens were selected as the representative bacterial species. Each bacterial suspension was inoculated into PAW immediately after generation, and the viable counts at different exposure times of 0·5, 1, 3, 5 and 24h during 4°C storage were measured to determine the inactivation efficacy. Scanning electron microscopy images of the bacteria were conducted to examine the structural changes. Physicochemical properties of PAW, including pH, conductivity, oxidation reduction potential (ORP), and reactive species of H2 O2 , NO2 - and NO3 - were measured. The results demonstrated that inactivation efficacy was in positive correlation with voltage and exposure time. Gram-negative bacteria were more susceptible to PAW than Gram-positive bacteria. Morphology damage was observed for all the bacterial species. PAW was significantly acidified, conductivity and ORP were significantly increased, and reactive species were detectable after 48h. This study offered a better understanding of the inactivation mechanisms of PAW, and the inactivation efficacy can be affected by voltage, exposure time and bacterial species. This study demonstrated the potential usage of PAW as an alternative disinfectant.

Study of the Characteristics of DC Multineedle-to-Water Plasma-Activated Water and Its Germination Inhibition Efficiency: The Effect of Discharge Mode and Gas Flow

In this article, a negative dc multineedle-to-water discharge device was designed to generate plasma-activated water (PAW) with a total volume of 580 mL. The physicochemical properties of PAW were investigated. The results showed that the products concentration of PAW and its acidity were not continuously increased by adding the applied voltage. When it turned from pulse corona discharge to DC glow-like discharge (−19.5 to −20.5 kV), the corresponding value decreased with the increase of the applied voltage. This decrease was attributed to the fact that the differences in the discharge figure had an effect on the reactions of transient species with N x O y in different discharge modes. In addition, by comparing the product concentrations of PAW in different gas conditions, we discovered that the gas flow would lead to a decrease of active species in PAW and its inactivation. Although the gas flow took away the N x O y diffused in the discharge chamber and formed microbubbles in the gas-washing bottle, which benefitted for increasing the absorption area with water, this process also took away NO out of the discharge area, which decreased its reaction with transient species such as OH, O2−, and O to form HNO2 and HNO3 directly. Finally, the germination inhibition rate (GIR) of penicillium spores was calculated to estimate the inactivation efficiency of PAW. The maximum GIR was 71.5% when the applied voltage was −19.5 kV (corona discharge) and the gas flow rate was 0 L/h.

Inactivation Effect of Colletotrichum Gloeosporioides by Long-Lived Chemical Species Using Atmospheric-Pressure Corona Plasma-Activated Water

In this paper, atmospheric-pressure air and oxygen corona plasma jets under water surface have been used to generate plasma-activated water (PAW) to inactivate colletotrichum gloeosporioides ( C. gloeosporioides ) suspension. The atmospheric-pressure plasma jets in the water were characterized by measuring: 1) the electrical and optical properties for evaluating the plasma efficiency and 2) the physicochemical properties of PAW, including pH value, oxidation-reduction potential value, and the concentration of hydrogen peroxide, nitrite, and ozone. The aim of this paper is to investigate the effects of long-lived reactive oxygen and nitrogen species (RONS) and environmental factor (acidity) in PAW on fungicidal property. The results of antifungal activity show that the inactivation rate of C. gloeosporioides is higher using air-PAW than oxygen-PAW, and increases with increasing reaction time when preparation time of PAW is fixed as 30 min. This correlates well with measurements of the aqueous-phase long-lived RONS concentration such as nitrate and ozone, suggesting these species play crucial roles in the inactivation process.

In vitro studies of the antimicrobial effect of non-thermal plasma-activated water as a novel mouthwash.

The aim of this study was to evaluate the antimicrobial effects of non-thermal plasma-activated water (PAW) as a novel mouthwash in vitro. Three representative oral pathogens - Streptococcus mutans, Actinomyces viscosus and Porphyromonas gingivalis - were treated with PAW. The inactivation effect was evaluated using the colony-forming unit (CFU) method, and the morphological and structural changes of a cell were observed by scanning electron microscopy and transmission electron microscopy (TEM). The physicochemical properties of PAW were analysed, and its influence on the leakage of intracellular proteins and DNA was evaluated. The results showed significant reduction of Streptococcus mutans within 60 s, of Actinomyces viscosus within 40 s, and of Porphyromonas gingivalis in less than 40 s. Scanning electron microscopy and TEM images showed that the normal cell morphology changed by varying degrees after treatment with PAW. Intracellular proteins (280 nm) and DNA (260 nm) leaked from all three species of bacteria after treatment with PAW. Reactive oxygen species (ROS), especially atomic oxygen (O), hydroxyl radical (˙OH), and hydrogen peroxide (H2 O2 ), were generated and led to strong oxidative stress and cell damage. These results suggest that PAW has potential use as a novel antimicrobial mouthwash.