High Voltage Atmospheric Cold Plasma Research Articles

A combination of high-voltage atmospheric cold plasma and cinnamaldehyde significantly increases inactivation of Salmonella enterica and Escherichia coli O157:H7 in raw pineapple juice

The main objective of this study was to determine the antibacterial effectiveness of high voltage atmospheric cold plasma (HVACP) alone or combined with cinnamaldehyde against S. enterica and E. coli O157:H7 in raw pineapple juice. Additional objectives were to evaluate sublethal injury in pathogen survivors and physicochemical properties of the juice. Juice with or without added cinnamaldehyde (100 μL/L) and inoculated with ∼7.0 log10 CFU/mL of S. enterica or E. coli O157:H7, was exposed to HVACP (70 kV, 60 Hz) for 0 (control), 1.0, 3.0, 5.0, and 7.0 min. HVACP or cinnamaldehyde alone failed to achieve a 5.0-log10 CFU/mL reduction of the pathogens. In contrast, reductions (log10 CFU/mL) from combined application of HVACP and cinnamaldehyde were 5.38 (S. enterica) and 5.60 (E. coli O157:H7) after 7.0 min (P<0.05) with significant sublethal injury in S. enterica survivors (P<0.05). The degrees Brix increased only in HVACP-treated juice without cinnamaldehyde (P<0.05). HVACP treatment for 3 or 7 min, decreased lightness but increased chroma and hue angle of the juice (P<0.05); however, color differences were not visually detectable. The combined use of HVACP and cinnamaldehyde can enhance the microbial safety of pineapple juice with minimal changes in the physiochemical properties evaluated in this study.

Acid Adaptation Enhances Tolerance of Escherichia coli O157:H7 to High Voltage Atmospheric Cold Plasma in Raw Pineapple Juice.

Pathogens that adapt to environmental stress can develop an increased tolerance to some physical or chemical antimicrobial treatments. The main objective of this study was to determine if acid adaptation increased the tolerance of Escherichia coli O157:H7 to high voltage atmospheric cold plasma (HVACP) in raw pineapple juice. Samples (10 mL) of juice were inoculated with non-acid-adapted (NAA) or acid-adapted (AA) E. coli to obtain a viable count of ~7.00 log10 CFU/mL. The samples were exposed to HVACP (70 kV) for 1-7 min, with inoculated non-HVACP-treated juice serving as a control. Juice samples were analyzed for survivors at 0.1 h and after 24 h of refrigeration (4 °C). Samples analyzed after 24 h exhibited significant decreases in viable NAA cells with sub-lethal injury detected in both NAA and AA survivors (p < 0.05). No NAA survivor in juice exposed to HVACP for 5 or 7 min was detected after 24 h. However, the number of AA survivors was 3.33 and 3.09 log10 CFU/mL in juice treated for 5 and 7 min, respectively (p < 0.05). These results indicate that acid adaptation increases the tolerance of E. coli to HVACP in pineapple juice. The potentially higher tolerance of AA E. coli O157:H7 to HVACP should be considered in developing safe juice processing parameters for this novel non-thermal technology.

Inactivation of Salmonella enterica and shiga toxin-producing Escherichia coli on desiccated shredded coconut by high voltage atmospheric cold plasma

The main objective of the present study was to determine the efficacy of dielectric barrier discharge (DBD) high voltage atmospheric cold plasma (HVACP) at 70 kV for inactivating Salmonella enterica and shiga-toxin-producing Escherichia coli (STEC) on desiccated shredded coconut. Additional objectives were to evaluate sub-lethal injury in pathogen survivors, and selected quality characteristics of the coconut as affected by HVACP. Shredded coconut inoculated with ∼7.74 log10 CFU/g S. enterica or STEC, was exposed to HVACP (70 kV) for 3–15 min (S. enterica) and up to 5 min (E. coli). Non-HVACP-treated, inoculated coconut served as control. Samples were held at 23 ± 1°C for 24 h after HVACP treatment, and analyzed for survivors via the plate count method using thin agar layer (TAL) media and selective (SEL) agar. For each pathogen, differences in numbers of survivors on TAL medium and selective agar were used to evaluate sub-lethal injury. Color and texture of the coconut were determined using a ColorFlex EZ Spectrophotometer and a TA. XT Plus C Texture Analyzer, respectively. HVACP treatments significantly decreased the initial numbers of viable S. enterica and STEC (p &amp;lt; 0.05) with more survivors consistently recovered on TAL media compared to selective agar. Reductions (log10 CFU/g) of STEC and S. enterica after 3 min of HVACP treatment were 1.97 and 1.56, respectively (p &amp;lt; 0.05) based on survivors on TAL medium. A greater extent of sub-lethal injury was observed in STEC survivors compared to S. enterica (p &amp;lt; 0.05). The TAL method allowed detection of sub-lethally injured pathogens in HVACP-treated coconut that would have otherwise remained undetected if only selective agar media were used. There were minimal changes in color and texture of the coconut after HVACP (70 kV) treatment for 12 min. Based on these results, HVACP (70 kV) has good potential for inactivating enteric pathogens in desiccated shredded coconut to improve the microbial safety of this popular food ingredient with minimal effect on product color and texture.

Trends in Food Pathogens Risk Attenuation.

Foodborne pathogens represent one of the most dangerous threats to public health along the food chain all over the world. Over time, many methods were studied for pathogen inhibition in food, such as the development of novel packaging materials with enhanced properties for microorganisms' growth inhibition (coatings, films) and the use of emerging technologies, like ultrasound, radio frequency or microwave. The aim of this study was to evaluate the current trends in the food industry for pathogenic microorganisms' inhibition and food preservation in two directions, namely technology used for food processing and novel packaging materials development. Five technologies were discussed in this study, namely high-voltage atmospheric cold plasma (HVACP), High-Pressure Processing (HPP), microwaves, radio frequency (RF) heating and ultrasound. These technologies proved to be efficient in the reduction of pathogenic microbial loads in different food products. Further, a series of studies were performed, related to novel packaging material development, by using a series of antimicrobial agents such as natural extracts, bacteriocins or antimicrobial nanoparticles. These materials proved to be efficient in the inhibition of a wide range of microorganisms, including Gram-negative and Gram-positive bacteria, fungi and yeasts.

Effect of high voltage atmospheric cold plasma on chicken eggs quality during refrigerated storage

Salmonellosis outbreaks caused by Salmonella Enteritidis are usually linked to the consumption of eggs and egg products. To assure egg safety, High Voltage Atmospheric Cold Plasma (HVACP) has demonstrated its efficacy in achieving higher than 105 CFU/egg reduction of this bacteria on the egg's surface. Although no quality changes were found immediately after treatment, there was a lack of knowledge on how the quality of HVACP-treated eggs could evolve during their shelf life, and a six-week quality study was performed in this work. Eggs were treated under two sets of conditions, 0.5 min of treatment within 24 h post treatment and 8.5 min of treatment and no post treatment time were the selected ones. No significant differences were found between untreated and treated eggs regarding albumen and yolk pH, Haugh unit, yolk color, vitelline membrane strength or shell strength. The changes detected during the six weeks of storage at 4 °C were attributed to the natural aging of the eggs and not to the effect of HVACP treatments. These results prove HVACP technology as an effective alternative to current techniques to assure both the safety and quality of eggs during their shelf life.

The Ru−Ni bimetallic catalyst activated by high-voltage atmospheric cold plasma (HVACP) and application in the isomerization of grape seed oil

Grape seed oil, as a high-linoleic acid type, can be used for the production of conjugated linoleic acid, which cannot be synthesized by the human body, through isomerization under the action of catalysts. Improving the activity of the catalyst is an effective way to obtain conjugated linoleic acid-rich edible oils. In this study, the Ru−Ni bimetallic catalyst was activated by high-voltage atmospheric cold plasma (HVACP) catalyst modification. The results showed that the specific surface area, pore size distribution, and average particle size of the Ru−Ni bimetallic catalyst were enhanced when the treatment condition was 180 s, the power at both ends of the plate was 150 W, and the gas composition was 5% H2/95% He. The catalyst characterization showed that the dispersion of the HVACP-treated Ru−Ni bimetallic catalyst was enhanced, which elevated the catalytic performance of the catalyst. Linoleic acid in grape seed oil was isomerized by the HVACP-treated Ru−Ni bimetallic catalyst, and grape seed oil rich in conjugated linoleic acid was obtained. The conjugated linoleic acid content, trans oleic acid content, peroxide value, and p-anisidine value were 42.52%, 0.63%, 5.01 mmol kg−1, and 12.41, respectively. Quantum chemical analysis further predicted the reaction sites and clarified the rationality of the isomerization reaction. This method provided a scientific basis for producing high-quality functional oils.

Degradation products of aflatoxin M1 (AFM1) formed by high voltage atmospheric cold plasma (HVACP) treatment

Cold plasma technology is a novel non-thermal technology that has shown promising results for food decontamination and improving food safety. This study is a continuation of a previous investigation of the treatment of AFM1-contaminated skim and whole milk samples by HVACP. Previous research has shown HVACP is effective in degrading aflatoxin M1 (AFM1) in milk. The goal of this study is to identify the degradation products of AFM1 after HVACP treatment in pure water. An HVACP direct treatment at 90 kV using modified air (MA65: 65% O2, 30% CO2, 5% N2) was performed for up to 5 min at room temperature on a 5.0 mL water sample in a Petri dish artificially contaminated with 2 μg/mL of AFM1. The degradants of AFM1 were analyzed and their molecular formulae were elucidated by using high-performance liquid-chromatography time-of-flight mass spectrometry (HPLC−TOF-MS). Three main degradation products were observed and based on mass spectrometric fragmentation pathways, chemical structures for the degradation products were tentatively assigned. According to the structure–bioactivity relationship of AFM1, the bioactivity of the AFM1 samples treated with HVACP was reduced due to the disappearance of the C8–C9 double bond in the furofuran ring in all of the degradation products.

Aflatoxin M1 degradation using high voltage atmospheric cold plasma (HVACP) technology

ABSTRACT Aflatoxins are one of the highly toxic secondary metabolites with high decomposition temperatures, ranging from 237 °C to 306 °C. Therefore, non-thermal treatments are preferred to ensure safe food while preserving food quality. High voltage atmospheric cold plasma (HVACP) is a novel non-thermal technology with the potential to reduce contaminants (e.g. mycotoxins) owing to reactive species such as ozone. Therefore, the aim of this study was to investigate the efficacy of HVACP to degrade Aflatoxin M1 (AFM1) in pure water. A dielectric barrier discharge HVACP was performed at 90 kV using modified air (MA65: 65% O2, 30% CO2, 5% N2) fill gas for 1, 3, and 5 min in a direct and indirect mode with no post-treatment or 4.0 h post-storage at room temperature. The chemical properties of water were evaluated. Ozone concentration in both gas and liquid phases was also measured. A 77% reduction of AFM1 was observed after 1 min of direct treatment with no post-treatment storage. The nitrate and peroxide contents after 1 min of direct treatment were 4.50 ± 0.70 and 9.5 ± 0.70 mg/L, respectively. Longer treatment time and direct mode of exposure resulted in a higher ozone concentration in either the gas or liquid phase. These results demonstrate the potential of HVACP as a non-thermal treatment for reducing AFM1 concentration. HVACP was capable of significantly degrading AFM1 using a very short treatment time and 4.0-h post-treatment storage.

Inactivation of Cronobacter sakazakii biofilms using high voltage atmospheric cold plasma on various food-contact surfaces-a preliminary study.

Cronobacter sakazakii is an opportunistic foodborne pathogen in powdered infant formula (PIF) associated with several foodborne outbreaks. Biofilms of C. sakazakii in the PIF manufacturing plant may be a source of contamination, but information on the treatment of these biofilms is limited. This study investigated the inactivation of C. sakazakii biofilms on three food contact surfaces (stainless steel, silicone, and PVC) using high voltage atmospheric cold plasma (HVACP) applied as a dielectric barrier discharge in a 10:90 air: helium modified atmosphere. After the 90 s of cold plasma exposure at 40 kV, C. sakazakii was reduced by ∼3 log CFU/coupon comparing to without cold plasma treatments. HVACP treatment caused cell shrinkage, fragmentation of the cell membrane, and leakage of cytoplasm. The inactivation of the cells on the surface was confirmed by live/dead staining. These above-mentioned results indicate the antibiofilm efficacy of HVACP on C. sakazakii isolates on various food contact surfaces.

Atmospheric Cold Plasma (ACP) Treatment for Efficient Disinfestation of the Cowpea Weevil, Callosobruchus maculatus

Highlights The exposure of C. maculatus to reactive gas species (RGS) from atmospheric cold plasma treatment (ACP) resulted in significant mortality at all life stages tested. Three-minute ACP treatments at voltages of 70 kV have the best insecticidal effect. The greatest impact of treatment was during the egg and young larval stages of C. maculatus. Abstract. The insecticidal capability and mechanism of high-voltage atmospheric cold plasma were studied using a dielectric barrier discharge reactor against Callosobruchus maculatus, a significant insect pest in stored grain degradation. The mortality rate of &amp;gt; 90.0% for egg and larval stages can be achieved with a longer treatment time of 3 minutes and a higher voltage of 70 kV. However, this treatment condition, paired with a post-treatment retention time of 4 days, is required to kill 95% of adult insects. The use of atmospheric cold plasma has a considerable impact on the mortality of a range of insect life stages. Sufficient toxicity can be achieved by plasma process management using modified atmospheric pressure with a working gas of 65% oxygen, 30% carbon dioxide, and 5% nitrogen to address the insect lifecycle phases that are vectors for pathogens, which can increase mycotoxin contamination and degrade grain quality. Introducing atmospheric cold plasma treatment as an alternative to chemical fumigation may provide a safer alternative for integrated pest management. Keywords: Atmospheric cold plasma (ACP), Cowpea weevil, Dielectric barrier, Insecticidal effect, Integrated pest management (IPM), Pesticide, Reactive gas species (RGS).

High voltage atmospheric cold plasma decontamination of Salmonella enteritidis on chicken eggs

Salmonella enteritidis (SE) accounts for more than 70% of Salmonella spp. infections in humans with a primary source being chicken eggs, that can result from post-lay SE cross-contamination of the shell from contaminated equipment or the environment. The objective of this study was to apply a HVACP treatment that can achieve a minimum 5-log reduction in SE on the surface of artificially inoculated shell eggs with an initial bacterial load of 108 CFU/egg, after a previous disinfection. Optimized HVACP treatment conditions were an indirect treatment with air at 60% humidity at 100 kV for one minute treatment and six hours post-treatment or alternatively, five minutes of treatment and four hours post-treatment. Egg quality parameters of Haugh unit (HU), pH, color, and vitelline membrane and shell strength were tested under the optimized conditions and showed no significant difference (p > 0.05) between treated and untreated eggs.Industrial relevance: Missing information for a possible scale up of a cold plasma system for egg surface decontamination has been addressed by an optimization of HVACP treatment focused on treatment and post-treatment time, essential parameters to have into account in the food industry. These results demonstrate that HVACP is an effective decontamination method for SE on chicken shell eggs and provides a baseline for a future scale up of the process, showing that different combinations of treatment variables can achieve the desired decontamination without affecting to key quality parameters of the egg such as Haugh Unit or vitelline membrane strength.

Degradation of Aflatoxin M1 in skim and whole milk using high voltage atmospheric cold plasma (HVACP) and quality assessment

Cold plasma technology is a novel non-thermal technology that has shown promising results for food decontamination and improving food safety. This study investigates the efficacy of high voltage atmospheric cold plasma (HVACP) system to reduce Aflatoxin M1 (AFM1) in skim and whole milk. A dielectric barrier discharge HVACP was employed at 90 kV using modified air (MA65: 65 % O2, 30 % CO2, 5 % N2) fill gas for 1,3, and 5 min. Skim and whole milk was spiked with 1.0 μg/L AFM1 and exposed to HVACP treatment in both direct or indirect mode with no post-treatment storage or 4.0 h post storage at room temperature. Optimum condition of toxin degradation was chosen as for quality assessment including color, conductivity, total dissolved solid (TDS), pH, viscosity, peroxide value (PV), Thiobarbituric acid reactive substance (TBARS) assay, Fourier-transform infrared spectroscopy (FTIR), as well as nutrient composition. A one-minute HVACP treatment degrades 41.9 % and 37.8 % of AFM1 in skim milk and whole milk, respectively. However, much greater reductions were seen after a short treatment and then post-treatment storage. A greater than 87 % reduction in AFM1 was observed for all samples after a 3 min HVACP treatment with 4.0 h of post treatment. These results suggest that a few minutes of HVACP treatment is sufficient to generate significant reactive plasma species in the milk. Quality changes were less significant with shorter post treatment time and indirect mode of exposure. Overall, HVACP is an effective solution for decontamination of milk from AFM1.

TMT-based proteomic analysis of the inactivation effect of high voltage atmospheric cold plasma treatment on Pseudomonas aeruginosa

Pseudomonas aeruginosa is a ubiquitous conditional pathogen. Cold plasma with a high inactivation efficacy becomes a potential decontamination technology. In this study, the inactivation effect of high voltage atmospheric cold plasma on P. aeruginosa was investigated through tandem mass tag quantitative proteomics analysis. After the treatment at 75 kV for 90 s, the mortality rate increased from 48.16% to 94.45% as post-treatment time extended to 2 h. A total of 469 proteins (246 being up-regulated and 223 being down-regulated) were identified as differentially expressed proteins. Bioinformatics analysis showed that differentially expressed proteins were mainly involved in energy metabolism, biofilm formation and quorum sensing, cell movement, protein secretion, DNA replication and repair, and RNA transcription and translation. The results indicated that energy generation was inhibited and the biofilm formation of P. aeruginosa became difficult after treatment. This paper deepens the understanding of the response of P. aeruginosa cells to high voltage atmospheric cold plasma treatment at the proteome level.

Effects of High Voltage Atmospheric Cold Plasma Treatment on the Number of Microorganisms and the Quality of Trachinotus ovatus during Refrigerator Storage.

In order to investigate the effects of high voltage atmospheric cold plasma (HVACP) treatment on the number of microorganisms in and the quality of Trachinotus ovatus during refrigerator storage, fresh fish was packaged with gases CO2:O2:N2 (80%:10%:10%) and treated by HVACP at 75 kV for 3 min; then, the samples were stored at 4 ± 1 °C for nine days. The microbial numbers, water content, color value, texture, pH value, thiobarbituric acid reactive substance (TBARS), and total volatile base nitrogen (TVB-N) values of the fish were analyzed during storage. The results showed the growth of the total viable bacteria (TVB), psychrophilic bacteria, Pseudomonas spp., H2S-producing bacteria, yeast, and lactic acid bacteria in the treated samples was limited, and they were 1.11, 1.01, 1.04, 1.13, 0.77, and 0.80 log CFU/g−1 lower than those in the control group after nine days of storage, respectively. The hardness, springiness, and chewiness of the treated fish decreased slowly as the storage time extended, and no significant changes in either pH or water content were found. The lightness (L*) value increased and the yellowness (b*) value decreased after treatment, while no changes in the redness (a*) value were found. The TBARS and TVB-N of the treated samples increased to 0.79 mg/kg and 21.99 mg/100 g, respectively, after nine days of refrigerator storage. In conclusion, HVACP can limit the growth of the main microorganisms in fish samples effectively during nine days of refrigerator storage with no significant negative impact on their quality. Therefore, HVACP is a useful nonthermal technology to extend the refrigerator shelf-life of Trachinotus ovatus.

Effects of High-Voltage Atmospheric Cold Plasma Treatment on Microbiological and Quality Characters of Tilapia Fillets.

Cold plasma (CP) has become an alternative to conventional thermal processing of food products. In this study, the effect of cold plasma treatment time on the inactivation and quality of tilapia fillets was investigated. The surfaces of tilapia fillets were inoculated with Salmonella enteritis (S. enteritis), Listeria monocytogenes (L. monocytogenes), and a mixture of both before being treated with cold plasma at 70 kV for 0, 60, 120, 180, 240, and 300 s. With the extension of treatment time, the number of colonies on the surface of the fillets decreased gradually; after 300 s of cold plasma treatment, S. enteritis and L. monocytogenes populations were reduced by 2.34 log CFU/g and 1.69 log CFU/g, respectively, and the a* value and immobile water content decreased significantly (p < 0.05), while the free water content increased significantly (p < 0.05). TBARS value increased significantly (p < 0.05) to 1.83 mg MDA/kg for 300 s treatment. The carbonyl value and sulfhydryl value of sarcoplasmic protein significantly (p < 0.05) increased and decreased, respectively, as treatment time extension, while no significant changes were found in myofibrillar protein. No significant differences were observed in pH, b* value, elasticity, chewiness, thiol value, and TVB-N value. The results showed that cold plasma had an inactivation effect on tilapia fillets and could preserve their original safety indicators. It was concluded that CP treatment could be used as an effective non-thermal method to maintain the quality of tilapia fillets and extend their shelf-life.

High voltage atmospheric cold plasma technology as a food safety intervention for decontamination of cutting tools during ready-to-eat poultry meat slicing

This study aimed to build a prototype that integrates a cold plasma capability into a manual meat slicer while it is in operation to minimize cross-contamination from the circular cutting blade. A high voltage atmospheric cold plasma (HVACP) generator was attached to a meat slicer with a rotating 22.5-cm diameter stainless steel slicing blade. The meat slicer with the installed cold plasma generator was contained within a sealed, clear acrylic box. Listeria innocua (LI) was selected as the test organism, and initial testing was performed on stainless-steel coupons in room air at a relative humidity ranging from 30 to 90% for treatment times up to 240 s. Results found that 240 s and 90% RH showed a 3.0-log reduction of LI. These conditions were then replicated using “dirty” stainless-steel knife while rotating. The results showed only a 0.5-log LI reduction. The gas was changed from air to MA65 gas blend (65% O2, 30% CO2 and 5% N2) and then a 1.91 log LI reduction was achieved on the “dirty” knife. Industrial relevanceDue to the rapid processing speeds required in the food industry, it is difficult to assure the complete cleanliness of the tools and surfaces used at all times, and then, operations like the cutting /slicing step are still one of the critical points for cross-contamination during meat processing. High voltage atmospheric cold plasma (HVACP) is a practical intervention that has the potential to deliver a continuous, in-situ decontamination of the knife during operation to mitigate the risk of cross-contamination. The developed prototype, as shown in this study, can deliver beneficial results in short treatment time and with minimal inputs of air and electricity, without heating effects, minimizing the use of water, or the use of sanitizers.

Alleviating Heavy Metal Toxicity in Milk and Water through a Synergistic Approach of Absorption Technique and High Voltage Atmospheric Cold Plasma and Probable Rheological Changes.

In this study, we combined atmospheric pressure cold plasma, a novel treatment technology, with an absorption technique with soybean husk to remove Pb and Cd from milk. Different combinations of treatment duration, voltage, and post treatment retention time were used to determine the effectiveness of cold plasma. Soybean husk was used for metal extraction, and it was observed that when the milk samples were plasma treated with a discharge voltage of 50 kV for 2 min and held for 24 h, the highest mean elimination of about 27.37% for Pb and 14.89% for Cd was obtained. Reactive oxygen and nitrogen species produced from plasma treatment were identified using Optical Emission Spectra analysis. A high voltage of 50 kV plasma for a 2 min duration could produce 500 ± 100 ppm of ozone concentration inside the treated package. The value of ΔE, which indicates overall color difference measurement, was significantly (p < 0.05) higher in all the treated samples than control samples. However, in the frequency range from 0.01 to 100 Hz, there was not much difference between the control and treated sample in the frequency sweep test. The identified functional groups at different wavenumbers (cm−1) in the treated samples were found to be similar compared to the control samples.

Ultrasound-Assisted High-Voltage Cold Atmospheric Plasma Treatment on the Inactivation and Structure of Lysozyme: Effect of Treatment Voltage

Emerging nonthermal processing techniques are gaining much attention due to their numerous advantages over traditional methods. Thus, in this study, high-voltage cold atmospheric plasma (HV-CAP) was employed separately and synergetically with ultrasound on lysozyme to investigate its activity and structure. The HV-CAP was operated at 120, 140, and 160 kV for 3 min at a frequency of 120 Hz. A significant difference was observed between the untreated and both treatments in lysozyme activity, with a more pronounced result in the ultrasound-assisted HV-CAP treatment. Both treatments resulted in the modification of the tertiary structure of the lysozyme as lipid oxidation, carbonyl content, UV spectra, intrinsic fluorescence, hydrophobicity, and sulphhydryl groups increased with increased voltage. Particle size distribution of lysozyme shows that noncovalent interactions affected the tertiary structure. The effects of both treatments on the secondary structure of lysozyme were demonstrated by CD and relative molar ellipticity. The results indicated that plasma-generated reactive species and ultrasound-induced cavitation influenced the unfolding of tertiary and secondary structures of the lysozyme. The CD spectra postulated that lysozyme inactivation was closely linked to the α-helix and β-sheet components of the secondary structure. This study presents an original novel knowledge on the modification of activity and structure of lysozyme subjected to ultrasound-assisted HV-CAP treatment that has been missing from the literature.Graphical abstract

Effects of high voltage atmospheric cold plasma treatment on microbial diversity of tilapia (Oreochromis mossambicus) fillets treated during refrigeration

Fresh tilapia fillets are susceptible to perish due to the microbial contamination during storage. High voltage atmospheric cold plasma (HVACP), a non-thermal technology, can effectively inactivate various microorganism. The aim of this study was to identify the microorganism amount and diversity changes of fresh tilapia fillets during refrigerator storage after HVACP treatment. Samples were treated at 70 kV for 1, 3 and 5 min by dielectric discharge barrier (DBD) cold plasma then stored at 4 °C. During the storage, amounts of Total viable bacteria (TVB), Psychrophilic bacteria, Pseudomonas spp., Lactic acid bacteria, Enterobacteriaceae, H2S-producing bacteria were measured, and microbial diversity of samples was analyzed. Long treatment time showed a great reduction effect on amounts of all bacteria. When tilapia fillets were treated at 70 kV for 5 min and stored for 12 d, amounts of TVB, Pseudomonas spp. and Enterobacteriaceae were 7.15, 6.99 and 4.23 log CFU/g, respectively, which were significantly lower (P < 0.05) than those in control group. High-throughput sequencing results showed that microbial diversity of tilapia fillets treated by HVACP was fluctuated as storage time extend, microbial species richness was decreased during first two days, and increased to the peak till 9 d, then decreased again. The dominant bacteria in fresh samples were Acinetobacter, Macrococcus, Pseudomonas, and Lactococcus. The abundance of both Acinetobacter and Macrococcus were decreased gradually during storage, while the abundance of Lactococcus was increased at first 3 d then decreased. After 12 d of storage, the dominant bacteria were transformed into Pseudomonas, Arthrobacter, and Kurthia.

Inactivation of spoilage organisms on baby spinach leaves using high voltage atmospheric cold plasma (HVACP) and assessment of quality

Cold plasma technology has previously shown potential as a novel, non-thermal technology for decontaminating foods and improving food safety. The study explores the potential of a nitrogen gas-based high voltage atmospheric cold plasma (HVACP) system to eliminate native microbiota from baby spinach leaves using a high purity (99.99%) nitrogen gas. The effect of HVACP was also evaluated over a storage period of 7 days at 4 °C. Up to 2.6 and 3.5 log10 CFU/sample of microbiota were eliminated until 7 days of refrigerated storage after 2.0 and 5.0 min (mins) of cold plasma exposure, respectively. 16 s rRNA sequencing revealed the presence of persistent Pseudomonas strains such as P. fluorescens, P. libanensis and Pseudomonas gessardii and elimination of other competitive microbial strains such as Bacillus spp., Exiguobacterium spp., and Pantoea spp. A five-minute, indirect, 80 kV HVACP treatment reduced 3.51 log10 CFU/sample after 7 days of refrigerated storage at 4 °C, compared to an untreated control with 7.50 log10 CFU/sample, without significantly affect the texture profile, color or moisture content of the leaves, serving as a promising non-destructive decontamination technology.