Plasma-activated Water Treatment Research Articles

Effect of Transient Spark Discharge and Plasma Activated Water Treatments against Fusarium graminearum Infected Wheat Grains under Laboratory Conditions

AbstractOver the last decade, more and more attention has been paid to applications of non-thermal plasma in agriculture, where it is used to decontaminate various microorganisms and to improve the seed germination. In this study, we present the results of a newly developed point-to-ring NTP transient spark discharge apparatus (NTP), plasma activated water (PAW) and their combined treatment on Durum wheat and Common wheat grains under laboratory conditions. Transient spark discharge treatment was used as direct treatment while indirect treatment of wheat grains was performed by PAW produced in point-to-plane NTP transient spark apparatus. We found that the degree of grain surface decontamination was in order NTP > PAW > combined treatment. In the case of Durum wheat grain germination, all treatments increased germination with increasing exposure times, while in the case of Common wheat, PAW treatment and combined treatment did not significantly increase the grain germination. In conclusion, plasma treatment has enormous potential for use in agriculture and its possibilities need to be fully explored.

Efficient inactivation effect of plasma‐activated water on oral pathogens Streptococcus mutans and Porphyromonas gingivalis

AbstractOral diseases stemming from oral pathogenic bacteria pose a significant global health concern, and current methods for managing these pathogens have limitations. Plasma‐activated water (PAW), containing various reactive species, emerges as a promising disinfectant with impressive inactivation capabilities. In this study, PAW prepared by mixed‐mode plasma‐activated gases was applied to inactivate oral pathogenic bacteria, including Streptococcus mutans and Porphyromonas gingivalis. The PAW could reduce more than 6.1‐log10 planktonic bacteria and 4.1‐log10 bacteria within biofilm, respectively, and PAW treatment of planktonic bacteria effectively inhibited biofilm formation. Compared to chlorhexidine, PAW exhibited superior inactivation effects in both planktonic bacteria and biofilm. This study presented a potent strategy for bacteria eradication to reduce the incidence of oral diseases.

Effects of incubation time of plasma activated water (PAW) combined with annealing for the modification of functional properties of potato starch

The present study investigates the application of annealing and plasma-activated water (PAW) for starch modification, as alternative methods compared to the chemical one. Native potato starch was subjected to PAW, annealing with distilled water (DW-ANN), and the combination of the two (PAW-ANN) at different incubation times (1, 4, 8, and 12 h). The changes in rheological, pasting, and thermal properties were evaluated. The results showed that all treatments promoted significant modifications of the investigated parameters. In particular, while the pasting properties of the potato starch remained unchanged after the PAW treatment, G’ (elastic) and G’’ (viscous) of the PAW-treated starch were significantly (p < 0.05) higher than those of the native. DW-ANN significantly increased all rheological parameters and reduced peak viscosity, breakdown, and setback and significantly (p < 0.05) incremented pasting temperature, holding strength, and final viscosities of the potato starch may be due to cross-linking reaction. The combination of treatment (PAW-ANN) showed a synergistic effect leading to strong gel formation up to 4 h, while further treatment reduced the possibility of depolymerization. In conclusion, the combined treatment is a promising new green method to modify the properties of starch and improve its stability within a short treatment time.

Stress response of Salmonella Newport with various sequence types toward plasma-activated water: Viable but nonculturable state formation and outer membrane vesicle production

This study aims to investigate the response of Salmonella Newport to plasma-activated water (PAW), a novel disinfectant that attracts attention due to its broad-spectrum antimicrobial efficacy and eco-friendliness. In this work, we demonstrated that S. Newport of different sequence types (STs) could be induced into the viable but nonculturable (VBNC) state by PAW treatment. Notably, a remarkable 99.96% of S. Newport ST45 strain entered the VBNC state after a 12-min PAW treatment, which was the fastest observed among the five S. Newport STs (ST31, ST45, ST46, ST166, ST2364). Secretion of outer membrane vesicles was observed in ST45, suggesting a potential strategy against PAW treatment. Genes related to oxidative stress (sodA, katE, trxA), outer membrane proteins (ompA, ompC, ompD, ompF) and virulence (pagC, sipC, sopE2) were upregulated in the PAW-treated S. Newport, especially in ST45. A reduction of 38–65% in intracellular ATP level after PAW treatment was observed, indicating a contributor to the formation of the VBNC state. In addition, a rapid method for detecting the proportion of VBNC cells in food products based on pagC was established. This study contributes to understanding the formation mechanism of the VBNC state in S. Newport under PAW stress and offers insights for controlling microbial risks in the food industry.

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.

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.

Plasma-activated water regulates water distribution to resist softening of goji berries

This study’s objective was to investigate the application of plasma-activated water (PAW) for treating goji berries and assess its effectiveness in preventing softening during storage. This objective was achieved by analyzing the water distribution and content of goji berries during storage using low-field nuclear magnetic resonance (LF NMR) and magnetic resonance imaging (MRI). The findings showed that PAW treatment shortened the relaxation time of T22 and T23, making the consistency of water freedom or binding degree of the four water environments in the treated goji berries higher compared with the control group. Furthermore, the PAW-treated group’s vacuolar and cell wall water contents were 4.532% and 86.544% at the late storage period; these values were all higher compared with the control group’s values. PAW treatment delayed the decrease of the goji berries’ vacuolar and cell wall water contents, reduced water loss, and regulated the water dynamic balance. In addition, the PAW treatment of goji berries increased the absorption peak of pectin at 1420 and 1735 cm−1, delayed the degradation of cell wall substances, and inhibited the deformation and damage of the cell wall structure; this resulted in a substantially higher pectin content compared with the control group (P < 0.05). Furthermore, the PAW-treated group’s polysaccharide content, hardness, and frangibility were 92.53 mg/g, 22.94 N, and 16.68 N respectively at the late storage period; these values were all higher compared with the control group’s values. The study’s results demonstrated that the PAW treatment of goji berries improves hardness and frangibility, reduces gumminess, and maintains texture characteristics, water content, and nutrients, especially polysaccharides, thereby delaying the softening process during storage.

LC-MS-based lipidomics analyses of alterations in lipid profiles of Asian sea bass (Lates calcarifer) induced by plasma-activated water treatment

A lipidomics approach based on liquid chromatography-mass spectrometry was employed to investigate alterations in lipid profiles within the muscles of Asian sea bass (ASB) (Lates calcarifer) post-treatment with plasms-activated water (PAW). Lipidomics studies detected 1500 diverse lipid types in ASB muscles; the phosphatidylcholine (PC) lipid subclass constituted the highest number of lipids (21.07 %), followed by triglycerides (TGs, 20.53 %) and phosphatidylethanolamine (PE, 12.73 %). Comparative analysis between PAW-treated ASB and raw ASB revealed the presence of differentially abundant lipids, with 48 lipids accumulating at high levels and 92 at low levels. Pathway enrichment analysis identified a total of seven lipid-related metabolic pathways; glycerophospholipid metabolism emerged as the predominant pathway. Furthermore, the content of saturated fatty acids in PAW-treated ASB increased from 1059.81 μg/g (raw ASB) to 1099.77 μg/g. Conversely, the content of monounsaturated and polyunsaturated fatty acids decreased from 645.81 μg/g and 875.02 μg/g to 640.80 μg/g and 825.25 μg/g, respectively. Collectively, these results indicate significant alterations in ASB lipid profiles following PAW treatment, establishing a theoretical foundation for understanding the mechanism involved in promoting lipid oxidation.

Plasma-activated water regulated transcriptome gene expression leading to high germination and growth of mung beans

BackgroundPlasma-activated water (PAW) is a solution created by exposing water to cold atmospheric plasma discharge, resulting in a biocidal agent with unique biochemical properties attributed to highly reactive oxygen and nitrogen species (RONS). Plasma-activated water (PAW) has been the subject of research for its potential in promoting seed germination. While it has shown promising results, the exact mechanism by which PAW promotes seed growth remains unclear. This study aims to investigate the role of PAW in promoting mung bean germination, including its effects on vitality improvement and the triggering of plant stress responses to promote crop growth. Through the utilization of next-generation sequencing, we aim to explore the interaction between the properties of PAW and gene expression in mung beans. By deciphering the nature of PAW and analyzing gene expression patterns, we hope to uncover the underlying mechanisms that govern their interaction.ResultsThe results revealed that nitrogen plasma-activated water (NPAW) treatment improves the vitality and hypocotyl length of mung beans and leads to a good overall growth state. Moreover, we identified numerous differentially expressed genes (DEGs), including genes related to stress responses, growth regulation, and metabolic processes, that were upregulated or downregulated in response to PAW treatment. As a result of APAW treatment, 168 genes were upregulated and 90 genes were downregulated. Furthermore, 179 genes were upregulated in the NPAW compared to 125 genes that were downregulated in the control group. Gene expression analysis revealed involvement in stress signaling and metabolic processes.ConclusionsPAW treatment can promote crop growth and serve as a reference for other seeds. This research provides insights into the regulatory mechanisms and benefits of PAW in sustainable agriculture.Graphical

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.

The Effect of Plasma-Activated Water Combined with Rosemary Extract (Rosmarinus officinalis L.) on the Physicochemical Properties of Frankfurter Sausage during Storage.

This study investigated the impact of plasma-activated water (PAW) and rosemary extract on the bacterial inactivation and quality attributes of Frankfurter sausages during a 6-day storage period. The antibacterial activity, total phenol content (TPC), and total flavonoid content (TFC) of the rosemary extract were evaluated. The TPC of the rosemary extract was 89.45 mg gallic acid/g dry weight, while the TFC was 102.3 mg QE/g dry weight. Even at low concentrations, the rosemary extract effectively inhibited the growth of all the tested pathogens using the Well Diffusion Agar method (WDA). The sausages were treated with different concentrations of PAW and rosemary extract and stored for 1 and 6 days. Sample B (100% rosemary extract + PAW treatment) showed the greatest reduction in microbial load and was selected for further analysis. Throughout the storage period, Sample B exhibited no significant changes in pH, moisture content, textural parameters, or sensory evaluation compared to the control group. However, the hardness and color parameters (L*, a*) of Sample B decreased, while the TBARS value increased after 6 days of storage. The combination of PAW and rosemary extract, particularly Sample B, effectively inhibited bacterial growth in the Frankfurter sausages without compromising most quality attributes. Some changes in hardness, color, and lipid oxidation were observed over the extended storage period.

Effect of plasma-activated water on the biofilm-forming ability of Salmonella enterica serovar Enteritidis and expression of the related genes

In recent years, microbial decontamination with plasma-activated water (PAW) has attracted a lot of research attention in the field of food industry. Despite several studies showing that PAW effectively inactivates planktonic bacteria, few studies have been conducted on biofilms. The present study was, therefore, designed to evaluate the effect of PAW on the biofilm formation characteristics of Salmonella Enteritidis. Comparing the expression patterns of biofilm-related genes in PAW-treated and non-treated planktonic and biofilm cells provided insight into how PAW regulates this process. The results showed that a 30-minute exposure to PAW at room temperature significantly reduced S. enteritidis planktonic cells. This exposure resulted in a decreased expression of the genes involved in the early stages of biofilm formation (csgD, agfA, fimA, lpfE, and rpoS), and an increased expression of the csrA gene in S. enteritidis planktonic cells. These results indicated the inhibitory effect of PAW on the biofilm formation process in S. enteritidis. Results of the initial attachment assay confirmed these findings, where, after 6 h, the number of PAW-treated cells attached to the stainless steel surfaces were significantly lower than non-treated ones. Furthermore, biofilm development assay revealed that the number of PAW-treated biofilm cells were significantly lower than non-treated ones after 24 h incubation at 37 °C. These findings were confirmed by measurements of the major components of biofilm i.e., extracellular DNA (eDNA), protein and carbohydrate. The amount of these components in 24-hour biofilms produced by PAW-treated S. enteritidis cells was significantly lower than that of non-treated cells. PAW's treatment on preformed 24-hour biofilms for 30 min led to a decrease in the expression of genes involved in quorum sensing and cellulose synthesis (csgD, bapA, adrA, luxS and sdiA) and an increase in the expression of the csrA gene. This treatment also reduced the number and metabolic activity of biofilm cells compared to non-treated biofilm cells. In total, the present study demonstrated that PAW has an inhibitory effect on the process of biofilm formation in S. enteritidis and hence, the food industry should pay special attention to PAW as a promising treatment to eliminate bacterial biofilms.

Impact of plasma-activated water on the supramolecular structure and functionality of small and large starch granules

Hydrothermal (HMT) and water agitation (WA) treatments using plasma-activated water (PAW) were employed as sustainable methods to modify the molecular and functional performance of small (rice) and large (potato) starch granules. HMT-PAW and WA-PAW treatments resulted in etched and damaged granular surfaces that rearranged the long and short-range crystallinity of the modified starches. Both treatments seemed to predominantly occur in the amorphous region of the rice starch and the crystalline regions of the potato starch, changing the crystallinity values from 22.9 and 14.8 % to 31.8 and 10.4 %, respectively. Thus, the level of the arrangement of chains reached after PAW treatment decreased the ability of rice starch granules to swell (16 to 9 %) and leach out starch molecules from the granules (4.5 to 1.3 %), decreasing the viscosity and pasting profiles as indicated by n and k values. Opposite behavior was observed in the modified potato starches since starch components leached out to a higher extent (1.7 to 5.4 %). The results showed that HMT and WA treatments using PAW are feasible eco-friendly methods for modifying starch granules without chemical reagents. These modified starches could be suitable as functional ingredients or biopolymeric matrices for the food and packaging industry.

Molecular insights: Proteomic and metabolomic dissection of plasma-induced growth and functional compound accumulation in Raphanus sativus

This study investigated the impact of plasma-activated water (PAW) on Raphanus sativus (radish) roots at the level of proteins and metabolites. PAW treatment induced the accumulation of reactive oxygen species (ROS) and nitrogen oxide species (NOx) in radish and enhanced the activities of antioxidant enzymes. Proteomic analysis resulted in the identification of 6054 proteins, including 1845 PAW-modulated proteins that were majorly associated with energy metabolism, ROS-detoxification, phytohormones signaling, and biosynthesis of glucosinolates. Subsequent metabolomics analysis identified 314 metabolites, of which 194 showed significant differences in response to PAW treatment. In particular, PAW treatment triggered the accumulation of functional compounds such as vitamin C, vitamin B5, glutathione, and glucosinolates, the well-known characteristic compounds of the Brassicaceae family. Further, integrating proteomics and metabolomics data provided novel insights into the molecular mechanism governing plasma-induced growth and the accumulation of these functional compounds in radish plants.

Plasma activated water as a pre-treatment strategy in the context of biofilm-infected chronic wounds

Healing and treatment of chronic wounds are often complicated due to biofilm formation by pathogens. Here, the efficacy of plasma activated water (PAW) as a pre-treatment strategy has been investigated prior to the application of topical antiseptics polyhexamethylene biguanide, povidone iodine, and MediHoney, which are routinely used to treat chronic wounds. The efficacy of this treatment strategy was determined against biofilms of Escherichia coli formed on a plastic substratum and on a human keratinocyte monolayer substratum used as an in vitro biofilm-skin epithelial cell model. PAW pre-treatment greatly increased the killing efficacy of all the three antiseptics to eradicate the E. coli biofilms formed on the plastic and keratinocyte substrates. However, the efficacy of the combined PAW-antiseptic treatment and single treatments using PAW or antiseptic alone was lower for biofilms formed in the in vitro biofilm-skin epithelial cell model compared to the plastic substratum. Scavenging assays demonstrated that reactive species present within the PAW were largely responsible for its anti-biofilm activity. PAW treatment resulted in significant intracellular reactive oxygen and nitrogen species accumulation within the E. coli biofilms, while also rapidly acting on the microbial membrane leading to outer membrane permeabilisation and depolarisation. Together, these factors contribute to significant cell death, potentiating the antibacterial effect of the assessed antiseptics.

An Effective Sanitizer for Fresh Produce Production: In Situ Plasma-Activated Water Treatment Inactivates Pathogenic Bacteria and Maintains the Quality of Cucurbit Fruit.

The effect of plasma-activated water (PAW) generated with a dielectric barrier discharge diffusor (DBDD) system on microbial load and organoleptic quality of cucamelons was investigated and compared to the established sanitizer, sodium hypochlorite (NaOCl). Pathogenic serotypes of Escherichia coli, Salmonella enterica, and Listeria monocytogenes were inoculated onto the surface of cucamelons (6.5 log CFU g-1) and into the wash water (6 log CFU mL-1). PAW treatment involved 2 min in situ with water activated at 1,500 Hz and 120 V and air as the feed gas; NaOCl treatment was a wash with 100 ppm total chlorine; control treatment was a wash with tap water. PAW treatment produced a 3-log CFU g-1 reduction of pathogens on the cucamelon surface without negatively impacting quality or shelf life. NaOCl treatment reduced the pathogenic bacteria on the cucamelon surface by 3 to 4 log CFU g-1; however, this treatment also reduced fruit shelf life and quality. Both systems reduced 6-log CFU mL-1 pathogens in the wash water to below detectable limits. The critical role of superoxide anion radical (·O2-) in the antimicrobial power of DBDD-PAW was demonstrated through a Tiron scavenger assay, and chemistry modeling confirmed that ·O2- generation readily occurs in DBDD-PAW generated with the employed settings. Modeling of the physical forces produced during plasma treatment showed that bacteria likely experience strong local electric fields and polarization. We hypothesize that these physical effects synergize with reactive chemical species to produce the acute antimicrobial activity seen with the in situ PAW system. IMPORTANCE Plasma-activated water (PAW) is an emerging sanitizer in the fresh food industry, where food safety must be achieved without a thermal kill step. Here, we demonstrate PAW generated in situ to be a competitive sanitizer technology, providing a significant reduction of pathogenic and spoilage microorganisms while maintaining the quality and shelf life of the produce item. Our experimental results are supported by modeling of the plasma chemistry and applied physical forces, which show that the system can generate highly reactive ·O2- and strong electric fields that combine to produce potent antimicrobial power. In situ PAW has promise in industrial applications as it requires only low power (12 W), tap water, and air. Moreover, it does not produce toxic by-products or hazardous effluent waste, making it a sustainable solution for fresh food safety.

Achieving improved efficiency for removal of aflatoxin B1 by combination use of cold atmospheric-pressure plasma and plasma-activated water

A novel approach was employed to remove aflatoxin B1 (AFB1), a very toxic metabolite from Aspergillus flavus (A. flavus), by using cold atmospheric-pressure plasma (CAP) and plasma-activated water (PAW) in combination. The results showed that CAP could efficiently degrade AFB1, while the PAW produced by CAP could further remove AFB1 with a relatively long treatment time. During the CAP processing, hydroxyl radical (·OH) was one of the dominant reactive species, which caused the hydroxylation at furan ring of AFB1, while in PAW treatment, singlet oxygen (1O2) was the major reactive agent for AFB1 degradation, which caused the destruction of the methyl group on the benzene side chain and oxidized the double bond of the terminal furan ring in the AFB1 molecule. This study therefore provides new guidance for the application of plasma technology in the treatment of fungal mycotoxins for food safety.

Study on the sterilization effect of plasma jet and plasma activated water on Streptococcus mutans

To explore the effects of plasma jet (PJ) and plasma activated water (PAW) on the sterilization of Streptococcus mutans ( S. mutans) and compare the advantages and disadvantages of the two methods, so as to provide a basis for plasma treatment of dental caries and to enrich the treatment means of dental caries, an atmospheric pressure plasma excitation system was built, and the effects of PJ and PAW on the sterilization rate of S. mutans and the changes of temperature and pH during treatment were studied under different excitation voltage ( U e ) and different excitation time ( t e ). The results showed that in the PJ treatment, the difference in the survival rate of S. mutans between the treatment group and the control group was statistically significant ( P = 0.007, d=2.66) when U e = 7 kV and t e = 60 s, and complete sterilization was achieved at U e = 8 kV and t e = 120 s in the PJ treatment. In contrast, in the PAW treatment, the difference in the survival rate of S. mutans between the treatment group and the control group was statistically significant ( P = 0.029, d = 1.71) when U e = 7 kV and t e = 30 s, and complete sterilization was achieved with PAW treatment when U e = 9 kV and t e = 60 s. Results of the monitoring of temperature and pH showed that the maximum temperature rise during PJ and PAW treatment did not exceed 4.3 °C, while the pH value after PAW treatment would drop to a minimum of 3.02. In summary, the optimal sterilization parameters for PJ were U e =8 kV and 90 s < t e ≤ 120 s, while the optimal sterilization parameters for PAW were U e = 9 kV and 30 s< t e ≤ 60 s. Both treatment methods achieved non-thermal sterilization of S. mutans, where PJ required only a smaller U e to achieve complete sterilization, while at pH < 4.7, PAW only required a shorter t e to achieve complete sterilization, but its acidic environment could cause some chemical damage to the teeth. This study can provide some reference value for plasma treatment of dental caries.

Evaluation of plasma-activated water: Efficacy, stability, physicochemical properties, and mechanism of inactivation against Escherichia coli

In this study, plasma-activated water (PAW) was prepared by discharge below the surface of sterile distilled water. In addition to physicochemical properties, the bactericidal effect and mechanism of action of PAW were studied using Escherichia coli as the target microorganism. The plasma treatment would cause an increase in the redox potential (ORP), electrical conductivity (EC), NO3− and NO2− content, and a decrease in the pH of the water. At the same time, the sterilization effect of PAW on E. coli was progressively stronger with both discharge and immersion time, up to a maximum of 4.25 log CFU/mL. In addition, the EC, NO3− and NO2− content, as well as the bactericidal efficacy of PAW decreased with increasing storage time. The properties and bactericidal effects did not change significantly after PAW thawing (p > 0.05). Finally, proteomics techniques were used to identify and classify the differential proteins before and after PAW treatment. PAW treatment induced a stress response in E. coli. Differential expression proteins of biological processes including the metabolism of phosphorus-containing compounds and the cellular response to stimuli, as well as various binding-related and membrane structure-related, were induced.

Inhibition of cell wall pectin metabolism by plasma activated water (PAW) to maintain firmness and quality of postharvest blueberry

Blueberry is a class of berries with high nutritional and economic value but has short shelf life due to its rapid softening at room temperature. This study investigated the effects of plasma-activated water (PAW) treatment on the softening quality and cell wall pectin metabolism of blueberries stored for 10 d at 25 °C after being immersed in PAW for 10 min. PAW was generated by plasma with different times (1 and 2 min), fixed frequency (10 kHz) and fixed voltage (50 kV). The analysis showed that the firmness of PAW-treated fruit significantly increased (P < 0.05) by 36.4% after 10 d storage. PAW treatment controlled the solubilization of pectin from water-insoluble to water-soluble. The activities of cell wall pectin-degrading enzymes like polygalacturonase (PG), β-galactosidase (β-Gal) and pectin methylesterase (PME) in PAW-treated blueberries decreased by 15.7%, 18.3%, and 27.9%, respectively, on day 10. After PAW treatment, blueberries also maintained better postharvest quality (firmness, colour, soluble solid content and anthocyanin content) and intact epidermal waxy and cell wall structure. These results suggested that PAW showed great potential for postharvest fresh-keeping of blueberry.