High Voltage Atmospheric Cold Plasma Treatment 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.

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.

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.

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.

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.

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.

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.

Control of aflatoxin M1 in skim milk by high voltage atmospheric cold plasma

Cold plasma has potential for the degradation of aflatoxins in corn and hazelnuts; however, this has not been demonstrated for aflatoxin in milk. In this study, the efficacy of high voltage atmospheric cold plasma (HVACP) on the reduction of aflatoxin M1 (AFM1) in skim milk improved with increasing treatment times (1-20 min), using gas containing 65% oxygen (MA65) rather than air, increasing voltage (60-80 kV) and reducing sample volume (30 mL-10 mL). Direct treatment was more effective than indirect treatment. AFM1 in milk was degraded by 65.0 % and 78.9 % by air and MA65 respectively in 20 min with no change in milk colour. The toxicity of AFM1 after treatment was assessed using a brine shrimp model. A five-minute HVACP treatment reduced the toxicity of AFM1 by 83.9 % based on the increase in brine shrimp survival. HVACP is a promising method to reduce AFM1 in milk.

High voltage atmospheric cold plasma inactivation of Listeria monocytogenes in fresh Queso Fresco cheese

Listeria (L.) monocytogenes is a significant pathogen found in ready-to-eat meat and dairy products. Soft cheeses, such as Queso Fresco cheese (QFC), are particularly sensitive to Listeria contamination, and occasionally serve as a source of food-borne illness outbreaks. In the present study, clinical and cheese isolates of L. monocytogenes were assayed for phenotypic characteristics following sub-lethal high voltage atmospheric cold plasma (HVACP) treatment. Reductions in biofilm formation, swimming motility, and growth dynamics were observed following HVACP treatment. Microbial enumeration of 1-, 10-, and 100-g fresh QFC following 0, 1, 2, or 3 min of HVACP demonstrated significant reductions in L. monocytogenes after 1 min (P-value <0.05), with increasing efficacy with prolonged exposure. A mass-dependent effect was observed between treatments of 1-, 10-, and 100-g QFC in regard to treatment efficacy. This result indicates that greater L. monocytogenes reduction on a larger QFC mass requires greater exposure of the L. monocytogenes to the reactive gas species. Optical absorption spectroscopy confirmed a reduction in reactive gas species for each log increase in QFC mass, however, an equivalent volume of inert foam resulted in increased reactive gas generation compared to QFC. In conclusion, we demonstrate both the application and limitations of HVACP treatments of QFC in the currently defined experimental parameters.

Effect of High-Voltage Atmospheric Cold Plasma Treatment on Germination and Heavy Metal Uptake by Soybeans (Glycine max).

The need to feed 9.9 billion people by 2050 will require the coordination of farming practices and water utilization by nutrient-dense plants and crops. High levels of lead (Pb), a toxic element that can accumulate in plants, can lead to toxicity in humans. With the development of novel treatment technologies, such as atmospheric cold plasma (ACP) and engineered nanoparticles (NPs), the time to germination and levels of heavy metals in food and feed commodities can be reduced. This study provides insight into the impact of plasma-activated water (PAW) on the germination rates and effects of soybean seeds, and the resultant combination effects of zinc oxide uptake in the presence of lead. Soybean seedlings were watered with PAW (treated for 3, 5, and 7 min at 30, 50, and 70 kV), and the germination and growth rate were monitored for 10 days. The germinated seedlings were then grown hydroponically in a nutrient solution, and the biomass of each example was measured. The PAW treatment that resulted in the best growth of soybean seeds was then exposed to Pb and zinc-oxide nanoparticles (ZnONPs) to investigate heavy metal uptake in the presence of nanoparticles. After acid digestion, the rate of heavy metal uptake by the soybean plants was evaluated using inductively coupled plasma-mass spectrometry. The PAW seeds grew and germinated more quickly, demonstrating that the plasma therapy had an effect. The rate of heavy metal uptake by the plants was also shown to be 5x lower in the presence of ZnONP.

Effect of metal salts on high‐voltage atmospheric cold plasma‐induced polymerization of acrylamide

AbstractAcrylamide polymerization in solution was successfully induced by high‐voltage atmospheric cold plasma (HVACP) treatment, using nitrogen gas. Addition of metal sulfates greatly increased acrylamide polymerization, with ZnSO4 and MgSO4 yielding 89% and 62% polyacrylamide polymer, respectively. Presence of excited nitrogen species during HVACP treatment was demonstrated using optical emission spectroscopy. Proton NMR (H1NMR) and attenuated total reflectance‐Fourier transform infrared spectroscopy were performed to verify the degree of polymerization. Rheology experiments and viscosity measurements showed that acrylamide samples treated with HVACP in the presence of ZnSO4, MgSO4 had higher viscoelastic moduli, and intrinsic viscosity (η) compared to those treated in deionized (DI) water, due to the higher degree of polymerization. Addition of ZnSO4 yielded the greatest viscoelastic moduli and intrinsic viscosity (the storage modulus was G' = 1.26·104 ± 1.8·103 Pa and the loss modulus was G" = 3.06·103 ± 1.10·103 Pa, and [η] ≈ 26 L/g). With MgSO4, the viscoelastic moduli were G' = 5.93·103 ± 1.40·103 Pa and G" = 1.60·103 ± 2.6·102 Pa, and (η) ≈ 4.7 L/g. In DI water G' = 1.55·103 ± 2.1·102 Pa and G" = 7.44·102 ± 1.37·102 Pa, and (η) ≈ 2. PAM prepared with ZnSO4 also had the highest molecular weight, as determined by mass spectroscopy. ZnCl2 and MgCl2 hindered acrylamide polymerization, highlighting the effect of the sulfate ions on acrylamide polymerization using HVACP treatment.

High voltage atmospheric cold plasma modification of bovine serum albumin

While atmospheric cold plasma has successfully inactivated biohazardous proteinaceous molecules (unwanted enzymes, prions, and allergens) and modified proteins with improved functionality, few studies have characterized plasma-protein interactions. This study investigates the physicochemical interactions, structural alteration, and reaction mechanisms of bovine serum albumin (BSA) subjected to high voltage atmospheric cold plasma (HVACP) generated by a dielectric barrier discharge in sealed bags packed with air or modified air (65% O2, 30% N2, 5% CO2). Treating 10 mL of BSA solution (50 mg/mL) with HVACP for 60 min changed the sample from transparent to yellow and induced protein precipitation. HVACP also induced protein unfolding, altered secondary structure (27% loss of α-helix), and increased disorder structure (10% increase of random coil). HVACP-treated protein increased in average size from 10 nm to 113 μm, with a broader size distribution after 60 min of HVACP treatment. SDS-PAGE and mass spectrometry showed the formation of new peptides from 1 to 10 kDa, indicating plasma-triggered peptide bond cleavage. Chemical analysis and mass spectrometry demonstrated oxidation and deamidation in HVACP-treated samples. This study illustrates that interactions between HVACP-induced reactive species and proteins may introduce structural alterations, protein aggregation, peptide cleavage, and side-group modifications to proteins in aqueous conditions.

High voltage atmospheric cold plasma treatment of Listeria innocua and Escherichia coli K-12 on Queso Fresco (fresh cheese)

High voltage atmospheric cold plasma (HVACP) is a non-thermal technology for effective decontamination of foods, resulting in safer and extended shelf-life products. Queso fresco (QF: fresh cheese) is a food product prone to Listeria monocytogenes contamination. Once QF gets contaminated post-manufacture, there is no additional treatment to remove pathogen contaminants. In this study, 10 g QF were inoculated with L. innocua and E. coli K-12 and treated with HVACP under direct mode of exposure in dry air and MA65 (65% O2, 30% CO2, 5% N2) gas blends for up to 5 min at 60 kV, 80 kV, and 100 kV. After 5 min treatment in dry air at 100 kV, a reduction of 1.4 log10 CFU/g and 3.5 log10 CFU/g was observed for L. innocua and E. coli K-12 after 24 h storage at 4 °C, respectively. Increasing voltage from 60 to 100 kV resulted in a higher production of reactive antimicrobial species, which led to greater bacterial reductions with minimal effects on product quality. Overall, minimal quality changes in pH, moisture, color and lipid oxidation were observed, while no significant (p ≥ 0.05) difference was found in the cheese texture profile after HVACP treatment.

Cytotoxicity assessment of Aflatoxin B1 after high voltage atmospheric cold plasma treatment

Aflatoxin B1 (AFB1) is a secondary metabolite produced by Aspergillus flavus and A. parasiticus, and is a known carcinogen in humans and animals. High voltage atmospheric cold plasma (HVACP) technology has already shown promise to decontaminate AFB1 in food and feed. This study aimed to investigate the cytotoxicity of AFB1 after HVACP treatment. AFB1 (100 μM) was treated at 85 kV with HVACP for 0, 2, 5, 10, and 20 min. HepG2 cells were exposed to HVACP-treated AFB1 for 72 h and assessed for cell viability, caspase-3 activity, DNA fragmentation, and protein carbonyls for each treatment time. Cell viability, caspase-3 activity, DNA fragmentation levels, and protein carbonyls contents of HepG2 cells exposed to HVACP-treated AFB1 after 20 min was not significantly different compared to non-exposed HepG2 cells (P > 0.05). However, their contents were significantly higher in non-exposed cells compared to the other HVACP treatment times (P < 0.01). Twenty minutes of HVACP treatment for AFB1 significantly reduced AFB1 cytotoxicity and oxidative damage and showed potential as a safe aflatoxin decontamination technology.

Effect of high voltage atmospheric cold plasma on extraction of fenugreek galactomannan and its physicochemical properties

Fenugreek is a good source of galactomannan, however, conventional methods for its extraction are generally time-consuming and have relatively low recovery rates. In this study, we applied high voltage atmospheric cold plasma (HVACP) as a pretreatment and investigated its effects on galactomannan extraction from dry fenugreek seeds and soaked seeds in NaCl solution, as well as its physicochemical properties. Results showed that HVACP treatment with air at 80 kV for 30 min caused apparent structural disruption on fenugreek seed surface and decreased the pH of extracting solution, resulting in increased galactomannan extraction yields, by 122% from soaked seeds and 67% from dry seeds. Galactomannan treated with HVACP had higher water-binding capacity, swelling index and viscosity, as well as lower melting enthalpy. HVACP treatment also altered the surface morphology of galactomannan due to plasma etching, but no significant changes in its molecular and crystalline structures were observed. The findings of this study prove that HVACP can be a green approach, in terms of reduced chemical use, to effectively enhance the extraction efficiency of fenugreek galactomannan and modify its functional properties, hence facilitate more diverse applications in both food and polymer industries.

Penetration and Microbial Inactivation by High Voltage Atmospheric Cold Plasma in Semi-Solid Material

Multiple studies have demonstrated atmospheric cold plasma as an effective non-thermal technology for inactivating bacteria, spores, and other microbial contaminants in foods and on non-food surfaces. However, few studies have applied this technique to semi-solid food within a package. This study evaluates the efficacy and the interaction mechanism of high voltage atmospheric cold plasma (HVACP) on Salmonella enterica serovar Typhi (S. enterica) inactivation in agar gels with different compositions. HVACP was generated by a dielectric barrier discharge in air and a modified atmosphere (MA65: 65% O2) in sealed bags. Agar gels of various densities with a pH indicator were inoculated with S. enterica (> 107 cfu) and exposed directly (between the electrode) or indirectly (adjacent to electrode) to 90 kV at 60 Hz for up to 1.5 h. HVACP treatment induced greater than 6 log10 (cfu) reduction in viable bacteria (both with air and MA65) in the plasma penetrated zone exhibiting a pH change. Inactivation of bioluminescent E. coli K12-lux cells in the plasma penetrated zone confirmed that the plasma, and its generated reactive species, inactivates microbes as it penetrates into the gel. A two-minute HVACP treatment resulted in greater than 5 log10 (cfu) S. enterica reduction in applesauce. In summary, these results demonstrate that HVACP can be an effective non-thermal technology to control or even eliminate bacteria populations in semi-solid foods.

Strategy to achieve a 5-log Salmonella inactivation in tender coconut water using high voltage atmospheric cold plasma (HVACP)

This study examined high voltage atmospheric cold plasma (HVACP) technology as a non-thermal intervention for inactivating Salmonella enterica serovar Typhimurium LT2 (ST2) in tender coconut water (TCW). Treatment with HVACP in air at 90 kV for 120 s inactivated 1.30 log10 of ST2. Development of a TCW stimulant suggested an interfering role of magnesium and phosphate salts with HVACP inactivation. Generation of reactive gas species, viz. ozone and hydrogen peroxides were found to be responsible for microbial inactivation. The addition of 400 ppm citric acid to the TCW effectively reduced ST2 by 5 log10 during HVACP treatment. Under these conditions, higher cellular leakage and morphological damage were observed in ST2. Minimal physico-chemical changes in TCW were observed with HVACP treatment, except for an 84.35% ascorbic acid loss (added externally). These results demonstrate a potential pathway for developing highly effective cold plasma treatments to preserve fruit and vegetable juices.

Effect of high voltage atmospheric cold plasma on inactivation of Listeria innocua on Queso Fresco cheese, cheese model and tryptic soy agar

High voltage atmospheric cold plasma (HVACP) is a novel technology which has shown promising results on microbial inactivation under low temperature, and thus offers opportunities on decontamination of biological materials. In this study, Listeria innocua spot inoculated tryptic soy agar (TSA), Queso Fresco cheese (QFC) and cheese model (CM) samples were treated with HVACP under direct and indirect mode of exposure in dry air gas environment for 5 min. After direct HVACP treatment, a reduction of 5.0, 3.5 and 1.6 log10 CFU/g was observed for TSA, CM and QFC, respectively. Direct plasma treatment was more effective in Listeria innocua inactivation on CM and QFC compared to indirect treatment. Surface analysis has shown that the differences in surface roughness and micro-structure of the substrate hugely impact the efficacy of the HVACP treatment by affecting the attachment of the bacteria cells on the surface and providing protective locations for the microbes within the surface.

Structures of Degradation Products and Degradation Pathways of Aflatoxin B1 by High-Voltage Atmospheric Cold Plasma (HVACP) Treatment.

High-voltage atmospheric cold plasma (HVACP) is a novel nonthermal decontamination technology that has potential for use in the food industry. In this study, HVACP was applied to treat pure aflatoxin B1 (AFB1) powder on a glass slide. AFB1 was degraded by 76% using a 5 min HVACP treatment in air having 40% relative humidity. The degradation products of AFB1 were separated, and their molecular formulas were elucidated using liquid-chromatography time-of-flight mass spectrometry (HPLC-TOF-MS). Six main degradation products were observed. The structures of the degradation products were further clarified via orbitrap mass spectrometry by means of fragmentation of the parental ions. Two degradation pathways were proposed on the basis of the structure of the degradation products. Among the six degradation products, two were ozonolysis products of AFB1. The appearance of the other four degradation products indicates that AFB1 was degraded by other reactive species besides ozone that were generated during HVACP treatment. Reactive oxygen gas species are suggested as the major agents for aflatoxin degradation during HVACP treatment. Two degradation pathways of AFB1 by HVACP treatment were proposed. One pathway involves reactions in which H•, OH•, CHO• radicals are added. The other involves epoxidation by HO2• radicals and oxidation of AFB1by the combined effects of the oxidative species OH•, H2O2, and O3. According to the structure-bioactivity relationship of AFB1, the bioactivity of the AFB1 samples subjected to HVACP treatment is significantly reduced because of the disappearance of the C8═C9 double bond in the furofuran ring in all of the major degradation products as well as the modification of the lactone ring, cyclopentanone, and the methoxyl group.