Inactivation kinetics of Bacillus cereus spores by Plasma activated water (PAW)

Cold Plasma-A Sustainable Energy-Efficient Low-Carbon Food Processing Technology: Physicochemical Characteristics, Microbial Inactivation, and Industrial Applications

Nonthermal technologies, mostly utilized for microbial inactivation and quality preservation in food, are attracting increased interest, particularly in nonthermal plasma. Cold plasma (CP) demonstrates favorable results, such as increased germination, enhanced functional and rheological characteristics, and the eradication of microorganisms. Consequently, CP is a novel technology in food processing that has significantly contributed to the prevention of food spoilage. This study highlights contemporary research on CP technology in food processing. This includes its use in microbial decontamination, shelf life extension, mycotoxin degradation, enzyme inactivation, and surface modification of food products. The CP generation techniques under low pressure, including glow discharge, radio frequency and microwave techniques, and atmospheric pressure, including dielectric barrier discharge (DBD), plasma jet, and corona discharge, are discussed. Additionally, the source for the generation of plasma-activated water (PAW) with its significant role in food processing is critically discussed. The CP is an effective method for the decontamination of several food materials like fruits, vegetables, meat, and low-moisture food products. Also, the review addressed the effects of CP on the physicochemical properties of foods and CP for pretreatment in various aspects of food processing, including drying of food, extraction of bioactive compounds, and oil hydrogenation. CP improved the drying kinetics of food, resulting in reduced processing time and improved product quality. Similarly, CP is effective in maintaining food safety and quality, removing the formation of biofilm, and also in reducing protein allergenicity. The review also underscored the importance of CP as a sterilizing agent for food packaging materials, emphasizing its role in enhancing the barrier characteristics of biopolymer-based food packaging materials. Therefore, it is concluded that CP is effective in the reduction of pathogenic microorganisms from food products. Moreover, it is effective in maintaining the nutritional and sensory properties of food products. Overall, it is effective for application in all aspects of food processing. There is a critical need for ongoing research on upscaling for commercial purposes.

Process Technologies for Disinfection of Food-Contact Surfaces in the Dry Food Industry: A Review

The survival characteristics of bacterial pathogens, including Salmonella spp., Listeria monocytogenes, Staphylococcus aureus, and Escherichia coli, in foods with a low water activity (aw) have been extensively examined and reported. Microbial attachment on the food-contact surfaces can result in cross-contamination and compromise the safety of low-aw foods. The bactericidal potential of various conventional and novel disinfection technologies has been explored in the dry food industry. However, the attachment behavior of bacterial pathogens to food-contact surfaces in low-aw conditions and their subsequent response to the cleaning and disinfection practices requires further elucidation. The review summarizes the elements that influence disinfection, such as the presence of organic residues, persistent strains, and the possibility of microbial biotransfer. This review explores in detail the selected dry disinfection technologies, including superheated steam, fumigation, alcohol-based disinfectants, UV radiation, and cold plasma, that can be used in the dry food industry. The review also highlights the use of several wet disinfection technologies employing chemical antimicrobial agents against surface-dried microorganisms on food-contact surfaces. In addition, the disinfection efficacy of conventional and novel technologies against surface-dried microorganisms on food-contact surfaces, as well as their advantages and disadvantages and underlying mechanisms, are discussed. Dry food processing facilities should implement stringent disinfection procedures to ensure food safety. Environmental monitoring procedures and management techniques are essential to prevent adhesion and allow the subsequent inactivation of microorganisms.

Distribution characteristics and seasonal variation of microbial communities in powdered infant formula processing environment

The powdered infant formula (PIF) processing environment, as an industrial production site, provides a habitat conducive to microbial aggregation and colonization. However, the distribution and dynamics of microbial communities within this environment remain inadequately characterized. In this study, microbial community analysis was conducted using high-throughput sequencing on samples collected from the full production chain of 8 PIF factories. The sampling encompassed various types (raw milk, staff, air, equipment, wall and ground, and others) during two different seasons (summer and winter). The microbial diversity, composition, and dominant species varied across different groups. Potential source tracking analysis revealed close interactions between staff, air, and surface samples, indicating a potential risk of microbial transfer between staff and the processing environment. The β-nearest taxon index based null model showed that stochastic processes predominantly governed microbial community assembly across all groups. Positive interspecies interactions within the network structure, observed across different seasons and sample types, played a vital role in stabilizing and assembling microbial communities. Notably, the microbiota association networks of summer were more complex but demonstrated higher susceptibility to external disturbances. Conversely, the network structure of surface samples was more robust than that of other types of samples. These findings have improved our understanding of the microbial community distribution patterns in PIF processing environments, facilitating the prospective prediction and assessment of potential microbial sources and contamination risks in the processing chain, which in turn guides the implementation of refined control measures.

Characterization of the Bacillus cereus spore killed by plasma-activated water (PAW)

Bacillus cereus (B. cereus) spore is one of the most easily contaminated bacterial spores. Plasma-activated water (PAW) has emerged as a potential method for microbial inactivation. The exterior pyridine-2,6-dicarboxylic acid (DPA) of spores was released after PAW oxidative stresses. The broken inner membrane and partially hydrolyzed cortex were represented. Some spores' architecture changed from a full and plump surface to these with wrinkles and indentations and even the shape shifted from oval to partly elongated irregular contraction. The detached exosporium, the devoid content, and the distinctly ruptured multilayer structure were exhibited. Young's modulus indicated that PAW may cause a body with reduced elasticity. The multiple resistances toward NaClO, NaCl, heat, UV, H2O2, and lysozyme uncovered that the compromise in the spore coat, the loss of the integrity of inner membrane permeability, the denatured proteins, the unsaturated DNA, the degradation of α/β-type small acid-soluble proteins (SASPs) and part inactivation of cortex lytic enzymes occurred. The changes in fatty acid compositions, lipid peroxidation, protein loss, and the inhibited activity of ATPase as well as the degraded and collapsed representative DNA/DPA/proteins Raman spectrum peaks also further confirmed the potential sites for spore death by PAW.

Inactivation effects of plasma-activated saline prepared by the mixed gases of discharged air and different gases

Plasma-activated water can efficiently inactivate pathogenic microorganisms and is considered to be a potent disinfectant in the medical, food, and agricultural industries. In this study, the air discharged by the gliding arc was mixed with different gases including O2, ambient air, synthetic air, and N2 at different flow rates to produce the activated gases, which were then activated gases were inducted into saline to prepare plasma-activated saline (PAS). The gaseous reactive species in the activated gases were composed of NO, NO2, and N2O5 and the aqueous reactive species in the PAS included H2O2, NO2 −, NO3 –, ⋅ OH , and 1O2 with different intensities, while the inactivation effects of the PAS also varied with the type and the flow rates of the mixed gases in the activated gases. The inactivation effects of the PAS treated by the discharged air mixed with O2, ambient air, and synthetic air started to become weak after 3 h placement. Scavenger analysis demonstrated that the 1O2 played a critical role in the inactivation process. This study indicated that air discharged by the gliding arc mixed with different gases could regulate the reactive species and the biological effects of PAS, providing insight into the preparation of PAS applied for disinfection.

Effect of Plasma-Activated Water on the Cellulase-Producing Strain Aspergillus niger A32

To investigate the effect and mechanism of plasma-activated water (PAW) on Aspergillus niger, PAW was prepared using a needle array-plate dielectric barrier discharge plasma system. The concentrations of long-lived reactive oxygen and nitrogen species (RONS), namely, H2O2, NO2-, and NO3-, in the PAW were 48.76 mg/L, 0.046 mg/L, and 172.36 mg/L, respectively. Chemically activated water (CAW) with the same concentration of long-lived RONS was also prepared for comparison. A. niger A32 was treated with PAW and CAW. After treatment, the treated strains were observed and analyzed with scanning electron microscopy (SEM) and transmission electron microscopy (TEM) to screen probable mutants. The results indicated that the pH, conductivity, and ORP values of PAW were 2.42, 1935 μS/cm, and 517.07 mV, respectively. In contrast, the pH and ORP values of CAW were 6.15 and 301.73 mV, respectively, which differed significantly from those of PAW. In addition, the conductivity of CAW showed no change. SEM and TEM analyses revealed that A. niger A32 treated with CAW exhibited less damage compared with the control. In contrast, A. niger A32 treated with PAW showed significant shrinkage, deformation, and exudate attachment over time. Following PAW treatment, after four passages, a high cellulase-producing stable mutant strain A-WW5 was screened, exhibiting a filter paper enzyme activity of 29.66 U/mL, a cellulose endonuclease activity of 13.79 U/mL, and a β-glucosidase activity of 27.13 U/mL. These values were found to be 33%, 38%, and 2.1% higher than those of the original fungus sample, respectively. In total, 116 SNPs and 61 InDels were present in the genome of the mutant strain A-WW5. The above findings indicate that the impact of PAW on A. niger is not only attributed to long-lasting H2O2, NO2-, and NO3- particles but also to other short-lived active particles; PAW is expected to become a new microbial breeding mutagen.

The influence of pH on the efficacy of oxidation-reduction potential (ORP) to predict chlorine disinfection of surrogate bacteria, Escherichia coli O157:H7 and Listeria monocytogenes in oxidant demand free conditions and fresh produce wash water

Oxidation-reduction potential (ORP) is commonly used as a rapid measurement of the antimicrobial potential of free chlorine during industrial fresh produce washing. The current study tested the hypothesis that ORP can act as a "single variable" measurement of bacterial (vegetative and endospores) inactivation effectiveness with free chlorine irrespective of the water pH value. This situation has on occasion been assumed but never confirmed nor disproven. Chlorine-dosed pH 6.5 and 8.5 phosphate buffer solutions were inoculated with Escherichia coli (E. coli), Listeria innocua (L. innocua), or Bacillus subtilis (B. subtilis) endospores. ORP, free chlorine (FC), and log reduction were monitored after 5 s (for E. coli and L. innocua) and up to 30 min (for B. subtilis spores) of disinfection. Logistic and exponential models were developed to describe how bacteria reduction varied as a function of ORP at different pH levels. Validation tests were performed in phosphate buffered pH 6.5 and 8.5 cabbage wash water periodically dosed with FC, cabbage extract and a cocktail of Escherichia coli O157:H7 (E. coli O157:H7) and Listeria monocytogenes (L. monocytogenes). The built logistic and exponential models confirmed that at equal ORP values, the inactivation of the surrogate strains was not consistent across pH 6.5 and pH 8.5, with higher reductions at higher pH. This is the opposite of the well-known free chlorine-controlled bacterial inactivation, where the antibacterial effect is higher at lower pH. The validation test results indicated that in the cabbage wash water, the relationship between disinfection efficiency and ORP was consistent with the oxidant demand free systems. The study suggests that ORP cannot serve as a reliable single variable measurement to predict bacterial disinfection in buffered systems. When using ORP to monitor and control the antibacterial effectiveness of the chlorinated wash water, it is crucial to take into account (and control) the pH.

Inhibition and Mechanism of Citral on Bacillus cereus Vegetative Cells, Spores, and Biofilms

Bacillus cereus causes food poisoning by producing toxins that cause diarrhea and vomiting and, in severe cases, endocarditis, meningitis, and other diseases. It also tends to form biofilms and spores that lead to contamination of the food production environment. Citral is a potent natural antibacterial agent, but its antibacterial activity against B. cereus has not been extensively studied. In this study, we first determined the minimum inhibitory concentrations and minimum bactericidal concentrations, growth curves, killing effect in different media, membrane potential, intracellular adenosine triphosphate (ATP), reactive oxygen species levels, and morphology of vegetative cells, followed by germination rate, morphology, germination state of spores, and finally biofilm clearance effect. The results showed that the minimum inhibitory concentrations and minimum bactericidal concentrations of citral against bacteria ranged from 100 to 800 μg/mL. The lag phase of bacteria was effectively prolonged by citral, and the growth rate of bacteria was slowed down. Bacteria in Luria-Bertani broth were reduced to below the detection limit by citral at 800 μg/mL within 0.5 h. Bacteria in rice were reduced to 3 log CFU/g by citral at 4000 μg/mL within 0.5 h. After treatment with citral, intracellular ATP concentration was reduced, membrane potential was altered, intracellular reactive oxygen species concentration was increased, and normal cell morphology was altered. After treatment with citral at 400 μg/mL, spore germination rate was reduced to 16.71%, spore morphology was affected, and spore germination state was altered. It also had a good effect on biofilm removal. The present study showed that citral had good bacteriostatic activity against B. cereus vegetative cells and its spores and also had a good clearance effect on its biofilm. Citral has the potential to be used as a bacteriostatic substance for the control of B. cereus in food industry production.

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.

Modelling inactivation kinetics of free and encapsulated probiotic cells in millet biscuit under different baking conditions

The rising popularity of probiotic food in the diet for improved health benefits leads to the development of new probiotic functional foods. In general, biscuit is a long-shelf-life snack product that can be consumed straight from the pack without further processing. Although the development of probiotic bakery products is an innovative approach to market expansion, the infusion of probiotics in biscuits to produce probiotic biscuits has not been explored because of the complexity of the baking process. Therefore, this study aimed to evaluate the impact of baking conditions (160, 180, 200, and 220 °C) on the viability of free and encapsulated probiotic Lactobacillus acidophilus NCDC 016 cells by adding them into biscuit dough separately and baking for up to 600 sec. The cells were encapsulated using 20 % maltodextrin and 8.51 % gum arabic as a wall material and spray drying at an inlet and outlet air temperature of 150 and 55 ± 2 °C, respectively. At different baking temperatures (160, 180, 200, and 220 °C), the viability of probiotic (free and encapsulated) cells, the physicochemical properties of biscuits, and the inactivation kinetics of cells were examined by withdrawing samples every 120 sec. The survivability of encapsulated cells was observed to be higher than free cells at 160 and 180 °C for 600 sec. The moisture content and water activity were found to be higher and lower, respectively for encapsulated probiotic biscuits than for the biscuit containing free cells. The observed results of higher cell viability at 200 °C, 360 sec (5.38 log CFU/g) than at 180 °C, 600 sec (5.02 log CFU/g) can be explained by the time-temperature combination. Thus, producing the probiotic biscuit at baking conditions of 200 °C and 360 min is possible, providing the cell viability of 5 log CFU/g of probiotic biscuit. Further, the inactivation kinetics of cells were predicted by log-linear, Weibull, log-logistic, Gompertz, and Buchanan models. Under all baking conditions, the log-linear model was the best model for describing the data of encapsulated and free cells.

Effect of novel and conventional food processing technologies on Bacillus cereus spores

This chapter provides a summary of the effect of thermal and non-thermal processing technologies on Bacillus cereus spores, a well-known pathogenic bacterium associated with foodborne illnesses. B. cereus has been frequently detected in rice, milk products, infant food, liquid eggs products and meat products all over the world. This Gram positive, rod-shaped, facultative anaerobe can produce endospores that can withstand pasteurization, UV radiation, and chemical reagents commonly used for sanitization. B. cereus spores can germinate into vegetative cells that can produce toxins. The conventional regime for eliminating spores from food is retorting which uses the application of high temperature (121 °C). However, at this temperature, there could be a significant amount of loss in the organoleptic and functional qualities of the food components, especially proteins. This leads to the research on the preventive measures against germination and if possible, to reduce the resistance before using a non-thermal technology (temperatures less than retorting-121 °C) for inactivation. This chapter reviews the development and success of several food processing technologies in their ability to inactivate B. cereus spores in food.

Bactericidal efficacy difference between air and nitrogen cold atmospheric plasma on Bacillus cereus: Inactivation mechanism of Gram-positive bacteria at the cellular and molecular level

As an emerging food processing technology, cold atmospheric plasma (CAP) has attracted great attention in the field of microbial inactivation. Although CAP has been proven to effectively inactivate a variety of foodborne pathogens, there is less research on the inactivation of Bacillus cereus, and the exact inactivation mechanism is still unclear. Elucidating the inactivation mechanism will help to develop and optimize this sterilization method, with the prospective application in industrialized food production. This study aims to explore the bactericidal efficacy difference between air and nitrogen CAP on B. cereus, a typical Gram-positive bacterium, and reveals the inactivation mechanism of CAP at the cellular and molecular level, by observing the change of the cell membrane, cell morphological damage, intracellular antioxidant enzyme activity and cellular biomacromolecules changes. The results showed that both air CAP and nitrogen CAP could effectively inactivate B. cereus, which was due to the reactive oxygen and nitrogen species (RONS) generated by the plasma causing bacterial death. The damage pathways of CAP on Gram-positive bacteria could be explained by disrupting the bacterial cell membrane and cell morphology, disturbing the intracellular redox homeostasis, and destroying biomacromolecules in the cells. The differences in active species generated by the plasma were the main reason for the different bactericidal efficiencies of air CAP and nitrogen CAP, where air CAP producing RONS with stronger oxidative capacity in a shorter time. This study indicates that air CAP is an effective, inexpensive and green technology for B. cereus inactivation, providing a basis for industrial application in food processing.

A review on plasma-activated water and its application in the meat industry

Meat is a nutritious food with a short shelf life, making it challenging to ensure safety, quality, and nutritional value. Foodborne pathogens and oxidation are the main concerns that lead to health risks and economic losses. Conventional approaches like hot water, steam pasteurization, and chemical washes for meat decontamination improve safety but cause nutritional and quality issues. Plasma-activated water (PAW) is a potential alternative to thermal treatment that can reduce oxidation and microbial growth, an essential factor in ensuring safety, quality, and nutritional value. This review explores the different types of PAW and their physiochemical properties. It also outlines the reaction pathways involved in the generation of short-lived and long-lived reactive nitrogen and oxygen species (RONS) in PAW, which contribute to its antimicrobial abilities. The review also highlights current studies on PAW inactivation against various planktonic bacteria, as well as critical processing parameters that can improve PAW inactivation efficacy. Promising applications of PAW for meat curing, thawing, and decontamination are discussed, with emphasis on the need to understand how RONS in PAW affect meat quality. Recent reports on combining PAW with ultrasound, mild heating, and non-thermal plasma to improve inactivation efficacy are also presented. Finally, the need to develop energy-efficient systems for the production and scalability of PAW is discussed for its use as a potential meat disinfectant without compromising meat quality.

Modeling of the inactivation kinetics of aerobic mesophiles and yeasts and molds natural microbiota in nonthermal plasma-treated pineapple (Ananas comosus) juice

The nonthermal plasma (NTP) technology is a promising nonthermal technology that can be employed for pasteurization of fruit juice. The effect of NTP on the natural microbiota, namely, aerobic mesophiles (AM), and yeasts and molds (YM) in pineapple juice were examined in the experimental range of 25-45 kV up to 10 min treatment time. At an applied voltage of 45 kV, the AM and YM count reductions of 4.7 and 4.1 log cfu/mL were obtained at the end of the 14-min treatment. The inactivation kinetics of microbes were attempted to be explained using nonlinear models, including Weibull + tail, Geeraerd, log-logistic, Coroller, and Cerf. The residual population (Nres ) model parameter in the Geeraerd model explained the tailing behavior of microbes. Furthermore, the estimated values for the scale parameter and destruction rate constants were used to describe the sensitive and resistant percentages of the microbial population. According to statistical parameters (R2 : 0.978-0.999, RMSE: 0.034-0.277) and validation indicators (accuracy factor: 1.013-1.152, bias factor: 0.985-1.12), all models performed well. Akaike's theory was used to select the best-fit model, and the Coroller model was shown to be the most accurate one for AM and YM, exhibiting the lowest Akaike increment (Δi  = 0). PRACTICAL APPLICATION: Nonthermal plasma may be used as an alternate nonthermal process for this product in order to meet customer appeal for safe and nutritious juice with minimal processing. The goal of this work was to produce a nutritious and safe pineapple juice by using nonthermal processing.

A Case Report of Enteric Fever Caused by Consumption of Lettuce

When Salmonella enterica serotype Typhi (S. Typhi) is present in the water, food supply, or both, it leads to the rapid development of typhoid fever. Because lettuce is an ideal host for S. Typhi's survival, lettuce grown in animal manure can be the probable source of typhoid fever. Prompt identification and proper antibiotic treatment can lessen the burden of typhoid fever on the public health system. A male farmer, age 29, was admitted to our hospital with a serious major complaint of abdominal pain, lack of appetite, and runny diarrhea. The newly hospitalized patient had a 2-week history of high-grade fever, abdominal pain, loss of appetite, watery diarrhea, back pain, and generalized body aches. Blood culture is the most accurate test for the diagnosis of typhoid fever. Blood culture was positive and showed sensitivity to ciprofloxacin and other drugs. To cure the typhoid, 500 mg of ciprofloxacin was administered twice daily for 7 days. Pathogenic components, species that are infected, and host immunity all play a role in typhoid fever pathogenesis. Typhoid fever is common in underdeveloped countries due to tainted food or hazardous water sources. This report's main goals are to draw attention to the significance of food safety procedures and to the potential dangers of consuming raw vegetables.

Mechanisms of bacterial inhibition and tolerance around cold atmospheric plasma

The grim situation of bacterial infection has undoubtedly become a major threat to human health. In the context of frequent use of antibiotics, a new bactericidal method is urgently needed to fight against drug-resistant bacteria caused by non-standard use of antibiotics. Cold atmospheric plasma (CAP) is composed of a variety of bactericidal species, which has excellent bactericidal effect on microbes. However, the mechanism of interaction between CAP and bacteria is not completely clear. In this paper, we summarize the mechanisms of bacterial killing by CAP in a systematic manner, discuss the responses of bacteria to CAP treatment that are considered to be related to tolerance and their underlying mechanisms, review the recent advances in bactericidal applications of CAP finally. This review indicates that CAP inhibition and tolerance of survival bacteria are a set of closely related mechanisms and suggests that there might be other mechanisms of tolerance to survival bacteria that had not been discovered yet. In conclusion, this review shows that CAP has complex and diverse bactericidal mechanisms, and has excellent bactericidal effect on bacteria at appropriate doses. KEY POINTS: • The bactericidal mechanism of CAP is complex and diverse. • There are few resistant bacteria but tolerant bacteria during CAP treatment. • There is excellent germicidal effect when CAP in combination with other disinfectants.

Inactivation mechanisms of atmospheric pressure plasma jet on Bacillus cereus spores and its application on low-water activity foods

Bacillus cereus spore is one of the most easily contaminated bacterial spores in low-water activity foods such as black pepper. Atmospheric-pressure plasma jet (APPJ) has emerged as an emerging and promising method for microbial inactivation in food processing. This study aimed to investigate the efficacy of APPJ in inactivating spores under various treatment parameters and to examine the resulting alterations in spore structures and internal membrane properties. Meanwhile, the practical application of APPJ for spore inactivation in black pepper was also evaluated. The results indicated that air-APPJ had superior spore inactivation capability compared to N₂ and O₂-APPJ. After 20 min of APPJ treatment (50 L/min, 800 W, and 10 cm), the reduction in spore count (>2 log CFU/g) was significantly greater than that achieved by heat treatment (80℃). The damage of inner membranes was considered as the major reason of the dried spore inactivation by APPJ treatment. Moreover, it achieved a reduction in spore count of > 1 log CFU/g on inoculated black pepper without significantly affecting its color and flavor. Although the antioxidant activity of black pepper was slightly reduced, the overall quality of the product was not considerably affected by plasma treatment. This study concluded that APPJ is an effective technique for spore inactivation, offering promising potential for application in the decontamination of low-water activity foods.

Bactericidal Effect of Underwater Plasma Treatment on Waste Brine from Kimchi Production Process and the Evaluation of Reusability of Plasma-Treated Waste Brine in Salting Kimchi Cabbage

Recycling waste brine from the Kimchi production process is an important environmental and industry issue. We applied an underwater plasma to reduce food-borne pathogens in the waste brine. The capillary electrodes supplied by alternating current (AC) bi-polar pulsed power were applied to treat 100 L of waste brine. The inactivation efficacy was analyzed using four different agars (Tryptic Soy Agar (TSA), Marine agar (MA), de Man Rogosa Sharpe Agar (MRS), and Yeast Extract-Peptone-Dextrose (YPD), respectively. The microbial population was reduced linearly with treatment time, irrespective of culturing medium. The inactivation followed the log-linear model (R²: 0.96-0.99). The reusability of plasma-treated waste brine (PTWB) was determined by five parameters (salinity, pH, acidity, reducing sugar, and the population of microorganisms) of salted Kimchi cabbage, and they were compared with newly made brine (NMB) and waste brine (WB), respectively. The results showed that the quality of salted Kimchi cabbage prepared by PTWB was not significantly different from that of NMB, indicating that the underwater plasma treatment is feasible to reuse waste brine in the salting process of Kimchi production.

Optimization of Plasma-activated Water and Validation of a Potential Surrogate for Salmonella for Future Egg Washing Processes

Plasma-activated water (PAW) is considered a novel sanitizer for the food industry due to the antimicrobial mechanisms exhibited by reactive oxygen and nitrogen species. The plasma operation parameters can affect the chemistry of PAW and can therefore influence its microbial inactivation efficacy. This study statistically optimized the operating conditions of PAW (activation time, distance from nozzle, and volume of water) using response surface methodology. Two optimized conditions of PAW were identified for the inactivation of planktonic cells of the avirulent strain of Salmonella Typhimurium MHM112 providing a minimum reduction of 6.3 log. All three operating parameters significantly affected the physicochemical characteristics (pH, ORP, EC, nitrite, and nitrate) and microbial inactivation efficacy of PAW. Mixing of small batches using the two optimized conditions to obtain larger volumes did not significantly change the microbial inactivation. However, there were significant reductions in nitrite and nitrate concentrations in PAW due to the mixing of batches while the pH and ORP values remained unaffected. The storage of large volumes of PAW for 25 min at 40-46°C, which is the commercial egg washing temperature in the United States, did not significantly impact S. Typhimurium MHM112 inactivation or the physicochemical characteristics of PAW. A validation study using a cocktail of six pathogenic strains of Salmonella revealed no significant differences in inactivation between the avirulent S. Typhimurium MHM112 and the pathogenic strains, suggesting that the avirulent S. Typhimurium MHM112 may serve as a surrogate for sanitation of S. enterica at the optimized conditions of PAW. The results obtained from this study are useful for our long-term goal of evaluating PAW efficacy in surface egg washing to inactivate Salmonella.

Efficacy of plasma activated saline in a co-culture infection control model

Plasma activated liquids have demonstrated antimicrobial effects and receive increasing attention due to the potential to strengthen the armoury of novel approaches against antibiotic resistant bacteria. However, the antibacterial activity and cytotoxic effects of these solutions need to be understood and balanced before exposure to humans. In this study, the antibacterial effects of plasma activated saline (PAS) were tested against Gram negative and positive bacteria, and HaCaT keratinocytes were used for cytotoxicity studies. For the first time, a co-culture model between these bacteria and eukaryotic cells under the influence of PAS has been described. Exposure of saline to plasma resulted in high concentrations of nitrate, hydrogen peroxide and a reduction of pH. PAS caused high antibacterial effects in the co-culture model, accompanied by high cytotoxic effects to the monolayer of mammalian cells. We present evidence and provide a deeper understanding for the hypothesis that upon treatment with PAS, chemical species generated in the liquid mediate high antimicrobial effects in the co-culture setup as well as mitochondrial depolarization and glutathione depletion in HaCaT cells and cell lysis due to acidic pH. In conclusion, PAS retains strong antibacterial effects in a co-culture model, which may have unintended negative biological effects on mammalian cells.

Effect of the pH on the Antibacterial Potential and Cytotoxicity of Different Plasma-Activated Liquids

In this study, different plasma-activated liquids were evaluated for their antimicrobial effects against Escherichia coli, as well as for their cytotoxicity on mammalian cells. The PALs were prepared from distilled (DIS), deionized (DI), filtered (FIL), and tap (TAP) water. Additionally, 0.9% NaCl saline solution (SAL) was plasma-activated. These PALs were prepared using 5 L/min air gliding arc plasma jet for up to 60.0 min of exposure. Subsequently, the physicochemical properties, such as, the oxidation-reduction potential (ORP), the pH, the conductivity, and the total dissolved solids (TDS) were characterized by a water multiparameter. The PALs obtained showed a drastic decrease in the pH with increasing plasma exposure time, in contrast, the conductivity and TDS increased. In a general trend, the UV-vis analyses identified a higher production of the following reactive species of nitrogen and oxygen (RONS), HNO₂, H₂O₂, NO₃^-, and NO₂^-. Except for the plasma-activated filtered water (PAW-FIL), where there was a change in the position of NO₂^- and NO₃^- at some pHs, The higher production of HNO₂ and H₂O₂-reactive species was observed at a low pH. Finally, the standardized suspensions of Escherichia coli were exposed to PAL for up to 60.0 min. The plasma-activated deionized water (PAW-DI pH 2.5), plasma-activated distilled water (PAW-DIS pH 2.5 and 3), and plasma-activated tap water (PAW-TAP 3.5) showed the best antimicrobial effects at exposure times of 3.0, 10.0, and 30.0 min, respectively. The MTT analysis demonstrated low toxicity of all of the PAL samples. Our results indicate that the plasma activation of different liquids using the gliding arc system can generate specific physicochemical conditions that produce excellent antibacterial effects for E. coli with a safe application, thus bringing future contributions to creating new antimicrobial protocols.

Application of Pinhole Plasma Jet Activated Water against Escherichia coli, Colletotrichum gloeosporioides, and Decontamination of Pesticide Residues on Chili (Capsicum annuum L.)

Plasma activated water (PAW) generated from pinhole plasma jet using gas mixtures of argon (Ar) and 2% oxygen (O2) was evaluated for pesticide degradation and microorganism decontamination (i.e., Escherichia coli and Colletotrichum gloeosporioides) in chili (Capsicum annuum L.). A flow rate of 10 L/min produced the highest concentration of hydrogen peroxide (H2O2) at 369 mg/L. Results showed that PAW treatment for 30 min and 60 min effectively degrades carbendazim and chlorpyrifos by about 57% and 54% in solution, respectively. In chili, carbendazim and chlorpyrifos were also decreased, to a major extent, by 80% and 65% after PAW treatment for 30 min and 60 min, respectively. E. coli populations were reduced by 1.18 Log CFU/mL and 2.8 Log CFU/g with PAW treatment for 60 min in suspension and chili, respectively. Moreover, 100% of inhibition of fungal spore germination was achieved with PAW treatment. Additionally, PAW treatment demonstrated significantly higher efficiency (p < 0.05) in controlling Anthracnose in chili by about 83% compared to other treatments.

Modelling of inactivation kinetics of Escherichia coli and Listeria monocytogenes on grass carp treated by combining ultrasound with plasma functionalized buffer

Linear (first-order) and non-linear (Weibull, biphasic, and log-logistic) models were evaluated for predicting the inactivation kinetics of Escherichia coli and Listeria monocytogenes on grass carp treated by a novel technique (UPFB) combining ultrasound (US) with plasma functionalized buffer (PFB). Results showed that UPFB was more effective for inactivating bacteria when compared with individual applications of US or PFB with reductions of 3.92 and 3.70 log CFU/g for Escherichia coli and Listeria monocytogenes, respectively. Compared with the linear model, the three non-linear models presented comparable performances and were more suitable for describing the inactivation kinetics with superior adj-R² (0.962-0.999), accuracies (0.970-1.006) and bias factors (0.995-1.031), and by assessing the strengths of evidence, weights of evidence and evidence ratios for the models, the biphasic model was identified as the best fit model. The current study provided new insights into the effective evaluation of decontamination methods.

Functional and bioactive properties of Larimichthys polyactis protein hydrolysates as influenced by plasma functionalized water-ultrasound hybrid treatments and enzyme types

The effects of plasma functionalized water (PFW) and its combination with ultrasound (UPFW) on the functional and bioactive properties of small yellow croaker protein hydrolysates (SYPHs) produced from three enzymes were investigated. Fluorescence and UV-Vis spectroscopy indicated that SYPHs tended to unfold with increasing intensity and shift in wavelengths to more flexible conformations under PFW and UPFW treatments. Particle size distribution and microstructure analysis revealed that treatments could disrupt aggregation of protein molecules to increase the roughness, specific surface area, and decrease the particle size of peptides during hydrolysis. The partially denatured structure of SYPHs induced by treatments increased the susceptibility of the fish proteins to exogenous enzymes, thereby accelerating the hydrolytic process to yield peptides with improved solubility, decreased emulsifying and foaming properties, and improved enzyme-specific antioxidant properties. The results revealed that the functionality of SYPHs was influenced by the treatment method and the enzyme type employed.

Effects of combined treatment of plasma activated liquid and ultrasound for degradation of chlorothalonil fungicide residues in tomato

The effects of combined treatment (PAL-U) of plasma-activated liquid (PAL) including plasma-activated water (PAW) and plasma-activated buffer solution (PABS) and ultrasound (U) for the degradation of chlorothalonil fungicide on tomato fruit was investigated. Distilled water and buffer solution were activated by radiofrequency plasma jet for durations of 1, 3, 5, and 10 min to obtain PAL₁ to PAL₁₀. Fruits were immersed in PAL for 15 min and also in distilled water with sonication for 15 min for individual treatments, and in PAL with sonication for 15 min for combined treatments. The maximum chlorothalonil fungicide residues were reduced by 89.28 and 80.23% for PAW₁₀-U and PABS₁₀-U, respectively. HPLC-MS characterization revealed chlorothalonil degradation pathway and formation of 2,4,5-trichloroisophthalonitrile, 2,4-dichloroisophthalonitrile, 4-chloroisophthalonitrile, isophthalonitrile and phenylacetonitrile as degradation products. Treatments also showed no negative effects on tomato quality. Therefore, PAL and PAL-U treatments could serve as effective methods for degrading pesticides on tomatoes.

Microbiological Food Safety of Seaweeds

The use of seaweeds in the human diet has a long history in Asia and has now been increasing also in the western world. Concurrent with this trend, there is a corresponding increase in cultivation and harvesting for commercial production. Edible seaweed is a heterogenous product category including species within the green, red, and brown macroalgae. Moreover, the species are utilized on their own or in combinatorial food products, eaten fresh or processed by a variety of technologies. The present review summarizes available literature with respect to microbiological food safety and quality of seaweed food products, including processing and other factors controlling these parameters, and emerging trends to improve on the safety, utilization, quality, and storability of seaweeds. The over- or misuse of antimicrobials and the concurrent development of antimicrobial resistance (AMR) in bacteria is a current worldwide health concern. The role of seaweeds in the development of AMR and the spread of antimicrobial resistance genes is an underexplored field of research and is discussed in that context. Legislation and guidelines relevant to edible seaweed are also discussed.

Optimisation of treatment conditions for reducing Shewanella putrefaciens and Salmonella Typhimurium on grass carp treated by thermoultrasound-assisted plasma functionalized buffer

A novel method of thermoultrasound-assisted plasma functionalized buffer (PFB) for decontaminating grass carp was evaluated using the Box-Behnken design (BBD) with processing variables including PFB generating voltage (PV), ultrasound treatment time (UT) and temperature (TP). The predicted models were found to be significant (p < 0.05) and displayed sufficient fitness with experimental data as indicated by non-significant (p > 0.05) lack of fit and high coefficient of determination (R2≥0.97) values. The optimum decontamination conditions for the responses of S. putrefaciens and S. Typhimurium were PV of 66 V, UT of 14.90 min and TP of 60 ℃, achieving reductions of 4.40 and 3.97 log CFU/g, respectively, with a desirability of 0.998. Among the variables, temperature presented higher significance for inactivating bacteria and the production of volatile basic nitrogen and lipid peroxidation under the optimized conditions were within the limits of freshness for grass carp. Additionally, the effects of PFB and the optimized thermoultrasound-assisted PFB decontamination were mild on the microstructure of grass carp with slight ruptures and loose myofibril structures, indicating the potential of thermoultrasound-assisted PFB for seafood products decontamination with reduced processing time.

Multivariate Optimization of the FLC-dc-APGD-Based Reaction-Discharge System for Continuous Production of a Plasma-Activated Liquid of Defined Physicochemical and Anti-Phytopathogenic Properties

To the present day, no efficient plant protection method against economically important bacterial phytopathogens from the Pectobacteriaceae family has been implemented into agricultural practice. In this view, we have performed a multivariate optimization of the operating parameters of the reaction-discharge system, employing direct current atmospheric pressure glow discharge, generated in contact with a flowing liquid cathode (FLC-dc-APGD), for the production of a plasma-activated liquid (PAL) of defined physicochemical and anti-phytopathogenic properties. As a result, the effect of the operating parameters on the conductivity of PAL acquired under these conditions was assessed. The revealed optimal operating conditions, under which the PAL of the highest conductivity was obtained, were as follows: flow rate of the solution equaled 2.0 mL min^-1, the discharge current was 30 mA, and the inorganic salt concentration (ammonium nitrate, NH₄NO₃) in the solution turned out to be 0.50% (m/w). The developed PAL exhibited bacteriostatic and bactericidal properties toward Dickeya solani IFB0099 and Pectobacterium atrosepticum IFB5103 strains, with minimal inhibitory and minimal bactericidal concentrations equaling 25%. After 24 h exposure to 25% PAL, 100% (1-2 × 10⁶) of D. solani and P. atrosepticum cells lost viability. We attributed the antibacterial properties of PAL to the presence of deeply penetrating, reactive oxygen and nitrogen species (RONS), which were, in this case, OH, O, O₃, H₂O₂, HO₂, NH, N₂, N₂⁺, NO₂^-, NO₃^-, and NH₄⁺. Putatively, the generated low-cost, eco-friendly, easy-to-store, and transport PAL, exhibiting the required antibacterial and physicochemical properties, may find numerous applications in the plant protection sector.

Assessment of the production of Bacillus cereus protease and its effect on the quality of ultra-high temperature-sterilized whole milk

Bacillus cereus is one of the most important spoilage microorganisms in milk. The heat-resistant protease produced is the main factor that causes rotten, bitter off-flavors and age gelation during the shelf-life of milk. In this study, 55 strains of B. cereus were evaluated, of which 25 strains with protease production ability were used to investigate proteolytic activity and protease heat resistance. The results showed that B. cereus C58 had strong protease activity, and its protease also had the highest thermal stability after heat treatment of 70°C (30 min) and 100°C (10 min). The protease was identified as protease HhoA, with a molecular mass of 43.907 kDa. The protease activity of B. cereus C58 in UHT-sterilized whole milk (UHT milk) showed an increase with the growth of bacteria, especially during the logarithmic growth phase. In addition, the UHT milk incubated with protease from B. cereus C58 at 28°C (24 h) and 10°C (6 d) were used to evaluate the effects of protease on the quality of UHT milk, including protein hydrolysis and physical stability. The results showed that the hydrolysis of casein was κ-CN, β-CN, and α_S-CN successively, whereas whey protein was not hydrolyzed. The degree of protein hydrolysis, viscosity, and particle size of the UHT milk increased. The changes in protein and fat contents indicated that fat globules floated at 28°C and settled at 10°C, respectively. Meanwhile, confocal laser scanning microscopy images revealed that the protease caused the stability of UHT milk to decrease, thus forming age gelation.

Inactivation effects and mechanisms of plasma-activated water combined with sodium laureth sulfate (SLES) against Saccharomyces cerevisiae

The present study aimed to elucidate the antifungal effect and underlying mechanism of plasma-activated water (PAW) combined with sodium laureth sulfate (SLES) against Saccharomyces cerevisiae. S. cerevisiae, initially at 6.95 log₁₀ colony-forming unit (CFU)/mL, decreased to an undetectable level following the synergistic treatment of PAW and SLES (0.50 mg/mL) for 20 min. After PAW treatment combined with SLES (2.5 mg/mL) for 30 min, the S. cerevisiae cells on polyethylene films also reduced to an undetectable level from the initial load of 5.84 log₁₀ CFU/cm². PAW + SLES treatment caused severe disruption of membrane integrity and increased lipid oxidation within the cell membrane and the intracellular reactive oxygen species levels in S. cerevisiae cells. Besides, the disruption of the mitochondrial membrane potential (∆ψm) was also observed in S. cerevisiae cells after treatment of PAW and SLES at 0.01 mg/mL for 5 min. These data suggest that the combined treatment of PAW and SLES causes oxidation injury to cell membranes and abnormal ∆ψm in S. cerevisiae, which may be eventually responsible for cell death. This study demonstrates the potential application of PAW combined with SLES as an alternative disinfection method. Key Points • PAW + SLES exhibited synergistic antifungal activity against S. cerevisiae. • PAW + SLES resulted in severe disruption of membrane integrity and permeability. • PAW + SLES induced accumulation of reactive oxygen species in S. cerevisiae cells.

Effect of plasma activated water and buffer solution on fungicide degradation from tomato (Solanum lycopersicum) fruit

This study investigated the effect of plasma-activated liquid (PAL) including plasma-activated water (PAW) and plasma-activated buffer solution (PABS) for the reduction of chlorothalonil (CTL) and thiram (THM) pesticide residues on tomato fruit. Results revealed that the PAL obtained by using atmospheric air as the feed gas, CTL residues were decreased to 85.3% and 74.2% and THM residues decreased to 79.47 and 72.21% after treatments with PAW₁₀ and PABS₁₀, respectively, and increasing the activation time caused a significant reduction in fungicide residues. In addition, CTL and THM residues were also decreased while increasing the activation time of PAL using Ar/O₂ as the feed gas, the concentrations of the CTL residues were decreased to 75.07 and 69.89% for PAW₁₀ and PABS₁₀, respectively and THM residues decreased to 65.89 and 61.91% for PAW₁₀ and PABS₁₀, respectively. Oxidation-reduction potential (ORP) and electrical conductivity (EC) were increased significantly after plasma treatment, while pH values of both solutions were decreased significantly with activation time. NO₃^- and NO₂^- concentrations of PAW increased significantly, while for PABS, NO₃^- concentration decreased but NO₂^-, with increasing the plasma activation time. Additionally, washing with PAW and PABS caused no notable negative impact on tomato fruit. Results confirmed that PAL treatments showed a significant reduction of CTL and THM fungicide residues (p < 0.05) in tomato without affecting the quality.

Risk of Bacillus cereus in Relation to Rice and Derivatives

Rice is a very popular food throughout the world and the basis of the diet of the citizens of many countries. It is used as a raw material for the preparation of many complex dishes in which different ingredients are involved. Rice, as a consequence of their cultivation, harvesting, and handling, is often contaminated with spores of Bacillus cereus, a ubiquitous microorganism found mainly in the soil. B. cereus can multiply under temperature conditions as low as 4 °C in foods that contain rice and have been cooked or subjected to treatments that do not produce commercial sterility. B. cereus produces diarrhoeal or emetic foodborne toxin when the consumer eats food in which a sufficient number of cells have grown. These circumstances mean that every year many outbreaks of intoxication or intestinal problems related to this microorganism are reported. This work is a review from the perspective of risk assessment of the risk posed by B. cereus to the health of consumers and of some control measures that can be used to mitigate such a risk.

Plasma-Activated Water (PAW) as a Disinfection Technology for Bacterial Inactivation with a Focus on Fruit and Vegetables

Plasma-activated water (PAW) is generated by treating water with cold atmospheric plasma (CAP) using controllable parameters, such as plasma-forming voltage, carrier gas, temperature, pulses, or frequency as required. PAW is reported to have lower pH, higher conductivity, and higher oxygen reduction potential when compared with untreated water due to the presence of reactive species. PAW has received significant attention from researchers over the last decade due to its non-thermal and non-toxic mode of action especially for bacterial inactivation. The objective of the current review is to develop a summary of the effect of PAW on bacterial strains in foods as well as model systems such as buffers, with a specific focus on fruit and vegetables. The review elaborated the properties of PAW, the effect of various treatment parameters on its efficiency in bacterial inactivation along with its usage as a standalone technology as well as a hurdle approach with mild thermal treatments. A section highlighting different models that can be employed to generate PAW alongside a direct comparison of the PAW characteristics on the inactivation potential and the existing research gaps are also included. The mechanism of action of PAW on the bacterial cells and any reported effects on the sensory qualities and shelf life of food has been evaluated. Based on the literature, it can be concluded that PAW offers a significant potential as a non-chemical and non-thermal intervention for bacterial inactivation, especially on food. However, the applicability and usage of PAW depend on the effect of environmental and bacterial strain-based conditions and cost-effectiveness.

A review on recent advances in plasma-activated water for food safety: current applications and future trends

Plasma-activated water (PAW), the water or solutions treated with atmospheric cold plasma, is an eco-friendly technique with minimal changes in food products, making it a befitting alternative to traditional disinfection methods. Due to its potential microbicidal properties, PAW has been receiving increasing attention for applications in the food, agricultural, and biomedical fields. In this article, we aimed at presenting an overview of recent studies on the generation methods, physicochemical properties, and antimicrobial activity of PAW, as well as its application in the food industry. Specific areas were well discussed including microbial decontamination of food products, reduction of pesticide residues, meat curing, sprouts production, and disinfection of food contact materials. In addition, the factors influencing PAW efficiency were also well illustrated in detail, such as discharge parameters, types and amounts of microorganisms, characteristics of the liquid solution and food products, and treatment time. Moreover, the strategies to improve the efficacy of PAW were also presented in combination with other technologies. Furthermore, the salient drawbacks of this technology were discussed and the important areas for future research were also highlighted. Overall, the present review provides important insights for the application of PAW in the food industry.

The Antibacterial Efficacy and Mechanism of Plasma-Activated Water Against Salmonella Enteritidis (ATCC 13076) on Shell Eggs

Eggs are one of the most commonly consumed food items. Currently, chlorine washing is the most common method used to sanitize shell eggs. However, chlorine could react with organic matters to form a potential carcinogen, trihalomethanes, which can have a negative impact on human health. Plasma-activated water (PAW) has been demonstrated to inactivate microorganisms effectively without compromising the sensory qualities of shell eggs. For this study, various amounts (250, 500, 750, or 1000 mL) of PAW were generated by using one or two plasma jet(s) at 60 watts for 20 min with an air flow rate at 6 or 10 standard liters per minute (slm). After being inoculated with 7.0 log CFU Salmonella Enteritidis, one shell egg was placed into PAW for 30, 60, or 90 s with 1 or 2 acting plasma jet(s). When 2 plasma jets were used in a large amount of water (1000 mL), populations of S. Enteritidis were reduced from 7.92 log CFU/egg to 2.84 CFU/egg after 60 s of treatment. In addition, concentrations of ozone, hydrogen peroxide, nitrate, and nitrite in the PAW were correlated with the levels of antibacterial efficacy. The highest concentrations of ozone (1.22 ppm) and nitrate (55.5 ppm) were obtained with a larger water amount and lower air flow rate. High oxidation reduction potential (ORP) and low pH values were obtained with longer activation time, more plasma jet, and a lower air flow rate. Electron paramagnetic resonance (EPR) analyses demonstrated that reactive oxygen species (ROS) were generated in the PAW. The observation under the scanning electron microscope (SEM) revealed that bacterial cells were swollen, or even erupted after treatment with PAW. These results indicate that the bacterial cells lost control of cell permeability after the PAW treatment. This study shows that PAW is effective against S. Enteritidis on shell eggs in a large amount of water. Ozone, nitrate, and ROS could be the main causes for the inactivation of bacterial cells.