Efficacy of chlorine dioxide gas in reducing Escherichia coli O157:H7 on apple surfaces

Viral Disinfection of Porous Fomites Utilizing a Bacteriophage Model and Chlorine Dioxide Gas

The pursuit of disinfecting porous materials or fomites to inactivate viral agents has special challenges. To address these challenges, a highly portable chlorine dioxide (ClO2) gas generation system was used to ascertain the ability of a gaseous preparation to inactivate a viral agent, the MS2 bacteriophage, when associated with potentially porous fomites of cloth, paper towel, and wood. The MS2 bacteriophage is increasingly used as a model to identify means of inactivating infectious viral agents of significance to humans. Studies showed that MS2 bacteriophage can be applied to and subsequently recovered from potential porous fomites such as cloth, paper towel, and wood. Paired with viral plaque assays, this provided a means for assessing the ability of gaseous ClO2 to inactivate bacteriophage associated with the porous materials. Notable results include 100% inactivation of 6 log bacteriophage after overnight exposure to 20 parts per million(ppm) ClO2. Reducing exposure time to 90 minutes and gas ppm to lower concentrations proved to remain effective in bacteriophage elimination in association with porous materials. Stepwise reduction in gas concentration from 76 ppm to 5 ppm consistently resulted in greater than 99.99% to 100% reduction of recoverable bacteriophage. This model suggests the potential of ClO2 gas deployment systems for use in the inactivation of viral agents associated with porous potential fomites. The ClO2 gas could prove especially helpful in disinfecting enclosed areas containing viral contaminated surfaces, rather than manually spraying and wiping them.

Development of chlorine dioxide sustained-release device using carboxymethyl cellulose-polyvinyl alcohol-β-cyclodextrin ternary hydrogel and a new sustained-release kinetic model

Owing to unique physiochemical and biological properties as well as the ability to be combined with a wide variety of materials for both biocompatibility and hydrophilia, carboxymethyl cellulose (CMC) is an excellent choice as a carrier. Loading Chlorine dioxide (ClO₂) into biodegradable carrier for its good disinfection performance and high safety factors has attracted significantattention. Therefore, in this study, we used ClO₂ as a model drug, and a sustained-ClO₂-gas-release gel was developed from degradable materials, such as carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA), and β-cyclodextrin (βCD), through a simple and benign crosslinking strategy. Notably, the gel had sustained-release property in a wide temperature range of 4-35 ℃ and released ClO₂ gas effectively for more than 30 days. Furthermore, a loss factor was proposed based on the incomplete release of the drug in the sustained release process to a chieve a good fit with the gas diffusion process. A new diffusion model was designed based on the Korsmeyer-Peppas model, and an excellent fit was obtained. This sustained-ClO₂-gas-release gel provides theoretical and technical guidance for the development of sustained-disinfectant-release agents for use in space and offers new insights into the sustained release model of skeleton-soluble hydrogels.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s10570-023-05070-6.

Conventional and non-conventional disinfection methods to prevent microbial contamination in minimally processed fruits and vegetables

Pandemic COVID-19 warned the importance of preparing the immune system to prevent diseases. Therefore, consuming fresh fruits and vegetables is essential for a healthy and balanced diet due to their diverse compositions of vitamins, minerals, fiber, and bioactive compounds. However, these fresh products grew close to manure and irrigation water and are harvested with equipment or by hand, representing a high risk of microbial, physical, and chemical contamination. The handling of fruits and vegetables exposed them to various wet surfaces of equipment and utensils, an ideal environment for biofilm formation and a potential risk for microbial contamination and foodborne illnesses. In this sense, this review presents an overview of the main problems associated with microbial contamination and the several chemicals, physical, and biological disinfection methods concerning their ability to avoid food contamination. This work has discussed using chemical products such as chlorine compounds, peroxyacetic acid, and quaternary ammonium compounds. Moreover, newer techniques including ozone, electrolyzed water, ultraviolet light, ultrasound, high hydrostatic pressure, cold plasma technology, and microbial surfactants have also been illustrated here. Finally, future trends in disinfection with a sustainable approach such as combined methods were also described. Therefore, the fruit and vegetable industries can be informed about their main microbial risks to establish optimal and efficient procedures to ensure food safety.

Effect of ultraviolet light treatment on microbiological safety and quality of fresh produce: An overview

Fresh and fresh-cut fruits and vegetables have been associated in several foodborne illness outbreaks. Although investigations from those outbreaks reported that the contamination with pathogenic microorganisms may occur at any point in the farm to fork continuum, effective control strategies are still being widely investigated. In that direction, the concept of hurdle technology involving a sequence of different interventions have been widely explored. Among those interventions, ultraviolet (UV) light alone or in combination with other treatments such as use of organic acids or sanitizer solutions, has found to be a promising approach to maintain the microbiological safety and quality of fresh and fresh-cut produce. Recent advances in using UV as a part of hurdle technology on the safety of fresh produce at different stages are presented here. Furthermore, this review discusses the mechanism of UV induced antimicrobial activity, factors that influence antimicrobial efficacy and its effect on produce. In addition, the challenges, and prospects of using UV irradiation as an intervention treatment were also discussed.

Integrated Analysis of Transcriptome and Metabolome Reveals the Mechanism of Chlorine Dioxide Repressed Potato (Solanum tuberosum L.) Tuber Sprouting

Sprouting is an irreversible deterioration of potato quality, which not only causes loss in their commercial value but also produces harmful toxins. As a popular disinfectant, ClO2 can inhibit the sprouting of potato tubers. Using transcriptomic and metabolomic approaches to understand the repressive mechanism of ClO2 in potato sprouting is yet to be reported. Sequencing the transcriptome and metabolome of potatoes treated with ClO2 in this study revealed a total of 3,119 differentially expressed genes, with 1,247 and 1,872 genes showing down- and upregulated expression, respectively. The majority of the downregulated genes were associated with plant hormone signal transduction, whereas upregulated differential genes were associated primarily with biological processes, such as phenylpropanoid biosynthesis and the mitogen-activated protein kinase (MAPK) signaling pathway. Metabonomic assays identified a total of 932 metabolites, with 33 and 52 metabolites being down- and upregulated, respectively. Downregulated metabolites were mostly alkaloids, amino acids, and their derivatives, whereas upregulated metabolites were composed mainly of flavonoids and coumarins. Integrated transcriptomic and metabolomic analyses showed that many different metabolites were regulated by several different genes, forming a complex regulatory network. These results provide new insights for understanding the mechanism of ClO2-mediated repression of potato sprouting.

A Review: Gaseous Interventions for Listeria monocytogenes Control in Fresh Apple Cold Storage

Listeria monocytogenes (L. monocytogenes) causes an estimated 1600 foodborne illnesses and 260 deaths annually in the U.S. These outbreaks are a major concern for the apple industry since fresh produce cannot be treated with thermal technologies for pathogen control before human consumption. Recent caramel apple outbreaks indicate that the current non-thermal sanitizing protocol may not be sufficient for pathogen decontamination. Federal regulations provide guidance to apple processors on sanitizer residue limits, organic production, and good manufacturing practices (GMPs). However, optimal methods to control L. monocytogenes on fresh apples still need to be determined. This review discusses L. monocytogenes outbreaks associated with caramel apples and the pathogen’s persistence in the environment. In addition, this review identifies and analyzes possible sources of contaminant for apples during cold storage and packing. Gaseous interventions are evaluated for their feasibility for L. monocytogenes decontamination on apples. For example, apple cold storage, which requires waterless interventions, may benefit from gaseous antimicrobials like chlorine dioxide (ClO₂) and ozone (O₃). In order to reduce the contamination risk during cold storage, significant research is still needed to develop effective methods to reduce microbial loads on fresh apples. This requires commercial-scale validation of gaseous interventions and intervention integration to the current existing apple cold storage. Additionally, the impact of the interventions on final apple quality should be taken into consideration. Therefore, this review intends to provide the apple industry suggestions to minimize the contamination risk of L. monocytogenes during cold storage and hence prevent outbreaks and reduce economic losses.

Fresh Produce Safety and Quality: Chlorine Dioxide's Role

Maintaining microbial safety and quality of fresh fruits and vegetables are a global concern. Harmful microbes can contaminate fresh produce at any stage from farm to fork. Microbial contamination can affect the quality and shelf-life of fresh produce, and the consumption of contaminated food can cause foodborne illnesses. Additionally, there has been an increased emphasis on the freshness and appearance of fresh produce by modern consumers. Hence, disinfection methods that not only reduce microbial load but also preserve the quality of fresh produce are required. Chlorine dioxide (ClO₂) has emerged as a better alternative to chlorine-based disinfectants. In this review, we discuss the efficacy of gaseous and aqueous ClO₂ in inhibiting microbial growth immediately after treatment (short-term effect) versus regulating microbial growth during storage of fresh produce (long-term effect). We further elaborate upon the effects of ClO₂ application on retaining or enhancing the quality of fresh produce and discuss the current understanding of the mode of action of ClO₂ against microbes affecting fresh produce.

Robustness of fermented carrot juice against Listeria monocytogenes, Salmonella Typhimurium and Escherichia coli O157:H7

Artisanal vegetable fermentations are regaining popularity in industrialized countries, but they could be prone to contamination with foodborne pathogens. By simulating home or small-scale restaurant fermentations, we evaluated the microbiological safety of spontaneous carrot juice fermentations. Raw carrot juice was spiked with Listeria monocytogenes, Salmonella enterica subsp. enterica Typhimurium and Escherichia coli O157:H7, and the microbial dynamics were followed throughout the entire fermentation process by cultivation and amplicon sequencing. In addition, the behavior of these pathogens was also monitored after addition of raw cucumber juice and storage under refrigerated conditions to mimic post-contamination issues. Although the numbers of the pathogens increased during the first phase of the fermentation, the pathogens were not able to persist throughout the fermentation. Their numbers fell below the detection limit after 8 days of fermentation at 20 °C. Further investigation using amplicon sequencing also showed that there was no major impact on the general microbial dynamics of the spontaneous carrot juice fermentation. This indicates that the artisanal carrot juice fermentation is a robust process which resists the persistence of pathogens. More caution is needed however when mixing the final fermented product with a raw juice. When simulating pathogen post-contamination, both Salmonella enterica and Escherichia coli were able to survive in the refrigerated fermented juice up to 10 days after the fermentation. Listeria monocytogenes was detected up to 8 days in the refrigerated juice. Pasteurization of the raw juice before adding it to the fermented product is thus recommended.

Chlorine Dioxide Controls Green Mold Caused by Penicillium digitatum in Citrus Fruits and the Mechanism Involved

Green mold caused by Penicillium digitatum is the main postharvest disease in citrus fruits. The goal of this study is to evaluate the antifungal activity of chlorine dioxide (ClO₂) against P. digitatum both in vivo and in vitro and to elucidate the underlying mechanism using flow cytometry and scanning electron microscopy. The results showed that 200-1800 mg/L of ClO₂ significantly inhibited the incidence of green mold on kumquats, mandarins, Peru's oranges, and grapefruits caused by P. digitatum. Additionally, 200 mg/L of ClO₂ significantly induced cell apoptosis of P. digitatum by increasing the fluorescence intensity of the mitochondrial membrane potential from 118 to 1225 and decreased the living cell rate from 96.8 to 6.1%. Further study demonstrated that the content of malondialdehyde and nucleic acid leakage (OD₂₆₀) of P. digitatum markedly increased, and the mycelial morphology was seriously damaged with increased ClO₂ concentration. These results indicated that ClO₂ could inhibit fungal growth by destroying the membrane integrity of P. digitatum, and the use of ClO₂ may be an alternative strategy to control green mold in postharvest citrus fruits.

Application of chlorine dioxide microcapsule sustained-release antibacterial films for preservation of mangos

In this study, fresh mangos were packed using a custom-made antimicrobial film coated with sustained-release chlorine dioxide microcapsules. We then compared physical and chemical indexes, such as weight loss rate, firmness, chromatic aberrations, soluble solids, vitamin C, titratable acid, and other nutritional indicators, to examine changes in the mango and film during storage. Our findings revealed that control mango showed loss of edible value and commercial value after 21 days of storage, and the chlorine dioxide microcapsule antibacterial film group still retains food value and commercial value. Cross-sectional scanning electron microscopy images of the used film showed that the polylactic acid film was smooth and flat, whereas cross-sections of the antimicrobial film showed that the film was covered with voids due to deliberate release of chlorine dioxide gas during the packaging process. Thus, the antibacterial film exhibited erosion and degradation. These findings provided important insights into the use of antimicrobial films for the packaging of fruits during storage, which is essential for promoting the application of solid chlorine dioxide antimicrobial film in packaging preservation.

Microbiology of Fresh-cut Mangoes Prepared from Fruit Sanitised in Hot Chlorinated Water

Whole mangoes ( Mangifera indica, cv. Chok Anun) were washed in water with or without chlorine (100 mg total chlorine/L) at 11.7 ºC and 50 ºC before slicing and packaging. Microbiological analysis of the whole fruit showed that the stem scar contained larger populations of microorganisms than the skin. Washing reduced populations at both sites and the effect was enhanced by the addition of chlorine and heating of the wash water. None of the treatments prevented transfer of contaminants to the flesh during slicing, and evidence of spoilage in the form of discrete fungal colonies was observed in samples stored for 1 week at 5 ºC. Several species of bacteria, yeast and mould were recovered from packaged slices, but yeast and moulds accounted for the bulk of the spoilage of microflora. Barriers to the growth of these microorganisms may be necessary to reduce the risk of microbial spoilage of mango slices manufactured under commercial conditions.

Inactivation of Salmonella on Eggshells by Chlorine Dioxide Gas

Microbiological contamination of eggs should be prevented in the poultry industry, as poultry is one of the major reservoirs of human Salmonella. ClO2 gas has been reported to be an effective disinfectant in various industry fields, particularly the food industry. The aims of this study were to evaluate the antimicrobial effect of chlorine dioxide gas on two strains of Salmonella inoculated onto eggshells under various experimental conditions including concentrations, contact time, humidity, and percentage organic matter. As a result, it was shown that chlorine dioxide gas under wet conditions was more effective in inactivating Salmonella Enteritidis and Salmonella Gallinarum compared to that under dry conditions independently of the presence of organic matter (yeast extract). Under wet conditions, a greater than 4 log reduction in bacterial populations was achieved after 30 min of exposure to ClO2 each at 20 ppm, 40 ppm, and 80 ppm against S. Enteritidis; 40 ppm and 80 ppm against S. Gallinarum. These results suggest that chlorine dioxide gas is an effective agent for controlling Salmonella, the most prevalent contaminant in the egg industry.

Current topics in active and intelligent food packaging for preservation of fresh foods

The purpose of this review is to provide an overview of current packaging systems, e.g. active packaging and intelligent packaging, for various foods. Active packaging, such as modified atmosphere packaging (MAP), extends the shelf life of fresh produce, provides a high-quality product, reduces economic losses, including those caused by delay of ripening, and improves appearance. However, in active packaging, several variables must be considered, such as temperature control and different gas formulations with different product types and microorganisms. Active packaging refers to the incorporation of additive agents into packaging materials with the purpose of maintaining or extending food product quality and shelf life. Intelligent packaging is emerging as a potential advantage in food processing and is an especially useful tool for tracking product information and monitoring product conditions. Moreover, intelligent packaging facilitates data access and information exchange by altering conditions inside or outside the packaging and product. In spite of these advantages, few of these packaging systems are commercialized because of high cost, strict safety and hygiene regulations or limited consumer acceptance. Therefore more research is needed to develop cheaper, more easily applicable and effective packaging systems for various foods.

Effectiveness of Active Packaging on Control of Escherichia Coli O157:H7 and Total Aerobic Bacteria on Iceberg Lettuce

Contaminated leafy green vegetables have been linked to several outbreaks of human gastrointestinal infections. Antimicrobial interventions that are adoptable by the fresh produce industry for control of pathogen contamination are in great demand. This study was undertaken to evaluate the efficacy of sustained active packaging on control of Escherichia coli O157:H7 and total aerobic bacteria on lettuce. Commercial Iceberg lettuce was inoculated with a 3-strain mixture of E. coli O157:H7 at 10(2) or 10(4) CFU/g. The contaminated lettuce and un-inoculated controls were placed respectively in 5 different active packaging structures. Traditional, nonactive packaging structure was included as controls. Packaged lettuce was stored at 4, 10, or 22 °C for 3 wk and sampled weekly for the population of E. coli O157:H7 and total aerobic bacteria. Results showed that packaging structures with ClO2 generator, CO2 generator, or one of the O2 scavengers effectively controlled the growth of E. coli O157:H7 and total aerobic bacteria under all storage conditions. Packaging structure with the ClO2 generator was most effective and no E. coli O157:H7 was detected in samples packaged in this structure except for those that were inoculated with 4 log CFU/g of E. coli O157:H7 and stored at 22 °C. Packaging structures with an oxygen scavenger and the allyl isothiocyanate generator were mostly ineffective in control of the growth of the bacteria on Iceberg lettuce. The research suggests that some of the packaging structures evaluated in the study can be used to control the presence of foodborne pathogens on leafy green vegetables.

Potential biodefense model applications for portable chlorine dioxide gas production

Development of decontamination methods and strategies to address potential infectious disease outbreaks and bioterrorism events are pertinent to this nation's biodefense strategies and general biosecurity. Chlorine dioxide (ClO2) gas has a history of use as a decontamination agent in response to an act of bioterrorism. However, the more widespread use of ClO2 gas to meet current and unforeseen decontamination needs has been hampered because the gas is too unstable for shipment and must be prepared at the application site. Newer technology allows for easy, onsite gas generation without the need for dedicated equipment, electricity, water, or personnel with advanced training. In a laboratory model system, 2 unique applications (personal protective equipment [PPE] and animal skin) were investigated in the context of potential development of decontamination protocols. Such protocols could serve to reduce human exposure to bacteria in a decontamination response effort. Chlorine dioxide gas was capable of reducing (2-7 logs of vegetative and spore-forming bacteria), and in some instances eliminating, culturable bacteria from difficult to clean areas on PPE facepieces. The gas was effective in eliminating naturally occurring bacteria on animal skin and also on skin inoculated with Bacillus spores. The culturable bacteria, including Bacillus spores, were eliminated in a time- and dose-dependent manner. Results of these studies suggested portable, easily used ClO2 gas generation systems have excellent potential for protocol development to contribute to biodefense strategies and decontamination responses to infectious disease outbreaks or other biothreat events.

Antimicrobial activity of controlled-release chlorine dioxide gas on fresh blueberries

The effect of chlorine dioxide (ClO2) gas on the safety and quality of blueberries was studied. In vitro studies revealed that both ClO2 gas fumigation and ClO2 direct contact in water killed food pathogen bacterium Escherichia coli and fruit decay pathogen fungus Colletotrichum acutatum. In vivo studies were conducted using noninoculated berries and berries inoculated with postharvest decay and foodborne pathogens. Berries were inoculated with either E. coli (5.2 log CFU/g) or C. acutatum (3.9 log CFU/g). Inoculated fruit were dried for 2 h at room temperature in a climate-controlled laboratory and packed in perforated commercial clamshells, with or without ClO2 pads, and stored at 10°C for up to 9 days. The effects of ClO2 on microbial populations and fruit firmness were monitored during storage. In the inoculation experiment, treatment with ClO2 reduced populations of E. coli and C. acutatum by 2.2 to 3.3 and 1.3 to 2.0 log CFU/g, respectively. For the noninoculated blueberries, the initial total aerobic bacteria count and the yeast and mold count were 4.2 and 4.1 log CFU/g, respectively. ClO2 treatment reduced total aerobic bacteria count and yeast and mold count by 1.5 to 1.8 and 1.3 to 1.7 log CFU/g, respectively. The firmness of both inoculated and noninoculated blueberries was maintained by ClO2 treatment. Thus, controlled-release ClO2 gas fumigation technology shows promise as an effective and practical antimicrobial agent in commercial clamshell packaging of blueberry and other fruits.

Development of chlorine dioxide releasing film and its application in decontaminating fresh produce

A feasibility study was conducted to develop chlorine dioxide (ClO(2) )-releasing packaging films for decontaminating fresh produce. Sodium chlorite and citric acid powder were incorporated into polylactic acid (PLA) polymer. Films made with different amounts of PLA (100 and 300 mg), percentages of reactant (5% to 60%), and ratios of sodium chlorite to citric acid (1:2 or 2:1) were prepared using a solvent casting method. The release of ClO(2) from the resultant films was activated by moisture. Increase of reactants in the films produced more ClO(2) while higher PLA content in the films resulted in less release of ClO(2) . The ratio of sodium chlorite to citric acid and activation temperature (22 °C compared with 10 °C) did not affect the ClO(2) release from the films. Antimicrobial efficacy of ClO(2) released from the films was evaluated using grape tomato as a model food. The results indicate that the films were activated by moisture from tomatoes in the package and the released ClO(2) reduced Salmonella spp. and Escherichia coli O157:H7 inoculated on the tomatoes to undetectable levels (<5 colony forming units (CFU)/tomato), achieving more than 3 log reduction. The film-treated tomatoes did not show significant changes in color and texture as compared to controls during storage at 10 °C for 21 d. This study demonstrated the technical feasibility for development of gaseous ClO(2) -releasing packaging system to enhance microbial safety and extend shelf life of fresh produce.

Inactivation of Escherichia coli O157:H7 on the intact and damaged portions of lettuce and spinach leaves by using allyl isothiocyanate, carvacrol, and cinnamaldehyde in vapor phase

Antimicrobials in the vapor phase might be more effective in inactivating Escherichia coli O157:H7 cells attached to leafy greens than aqueous antimicrobials. We determined the activity of allyl isothiocyanate (AIT), cinnamaldehyde, and carvacrol against E. coli O157:H7 on intact and damaged lettuce and spinach tissue. Samples were treated with various concentrations of antimicrobial in the vapor phase at 0, 4, and 10 degrees C in an enclosed container. On intact lettuce surface, the vapor of the lowest concentration of these antimicrobials inactivated >4 log of E. coli O157:H7 at 0 and 4 degrees C in 4 days and at 10 degrees C in 2 days. However, at the tissue damaged by cutting, the highest concentration reduced the population by 4 log at 0 degrees C and 2 to 4 log at 4 degrees C in 4 days. These concentrations also reduced the population of the pathogen by 1 to 3 log at 10 degrees C in 2 days. The pathogen population on spinach surface was reduced by 1 log less than on lettuce surface. However, reduction of the pathogen within spinach tissue was 2 and 3 log less than within lettuce tissue at 0 and 4 degrees C, respectively. Overall, greater inactivation occurred on lettuce than spinach leaves and on the leaf surfaces than at the damaged area. Using antimicrobials in the vapor phase may improve the safety of refrigerated leafy greens marketed in sealed packages.

Chlorine dioxide gas from an aqueous solution: reduction of Salmonella in wounds on tomato fruit and movement to sinks in a treatment chamber

Chlorine dioxide (ClO2) off-gassed from an aqueous solution and reacted incrementally with potassium iodide solutions (sinks). After 30 min, 45% of the initial dose was detected as chlorite ion in the sink, whereas 35% of the initial dose was still in the source. Aqueous solutions of ClO2 can be used as a source of ClO2 gas in various laboratory experiments involving treatment of fruits or vegetables. Movement from source to sink is continuous, which precludes the development of large headspace concentrations and the need for a tight chamber seal. When the source solution has dissipated, the chamber can be opened safely as there is little free ClO2 remaining in the headspace. In tests with whole, wound-inoculated tomato fruit, at both green and pink stages of ripeness, the control of Salmonella enterica serotype Typhimurium in wounds varied with the weight of gas used. The number of viable cells of Typhimurium recovered was reduced by > 5 log units when > or = 0.5 mg of ClO2 was applied to three pieces of fruit during a 2-h treatment.

Inactivation of Salmonella and Escherichia coli O157:H7 on sliced and whole tomatoes by allyl isothiocyanate, carvacrol, and cinnamaldehyde in vapor phase

Little is known about the effectiveness of antimicrobials in the vapor phase for control of pathogens on the surface of fresh produce. We determined the activity of allyl isothiocyanate (AIT), cinnamaldehyde, and carvacrol against Salmonella and Escherichia coli O157:H7 on sliced and whole tomatoes. Samples were treated with various concentrations of antimicrobial in the vapor phase at 4, 10, and 25 degrees C in a closed container. AIT exhibited the highest antimicrobial activity followed by cinnamaldehyde. The lowest level of AIT (8.3 microl/liter of air) inactivated Salmonella on sliced tomatoes by 1.0 and 3.5 log at 4 and 10 degrees C, respectively, in 10 days and by 2.8 log at 25 degrees C in 10 h. This level of AIT inactivated Salmonella on whole tomatoes to the detection limit of <2 log CFU per tomato at 4 and 10 degrees C in 10 days and by 1.3 log CFU per tomato at 25 degrees C in 10 h. AIT also inactivated E. coli O157:H7 on sliced tomatoes by 3.0 log at 4 and 10 degrees C in 10 days, but there was no inactivation at 25 degrees C in 10 h. AIT reduced E. coli O157:H7 on whole tomatoes surface by 3.0 and 1.0 log CFU per tomato at 4 and 10 degrees C, respectively, in 10 days and by 2.0 log CFU per tomato at 25 degrees C in 10 h. Overall, greater inactivation occurred at 10 than at 4 degrees C and on the tomato surface than between slices. Antimicrobials in vapor phase may be useful for controlling pathogens on fresh tomatoes marketed in packages containing enclosed headspace.

Efficacy of gaseous chlorine dioxide as a sanitizer against Cryptosporidium parvum, Cyclospora cayetanensis, and Encephalitozoon intestinalis on produce

The efficacy of gaseous chlorine dioxide to reduce parasite and bacterial burden in produce was studied. Basil and lettuce leaves were inoculated with Cryptosporidium parvum and Cyclospora cayetanensis oocysts, Encephalitozoon intestinalis spores, and a cocktail of two isolates of nalidixic acid-resistant Escherichia coli O157:H7. The inoculated samples were then treated for 20 min with gaseous chlorine dioxide at 4.1 mg/liter. Cryptosporidium had a 2.6 and 3.31 most-probable-number log reduction in basil and lettuce, respectively. Reduction of Encephalitozoon in basil and lettuce was 3.58 and 4.58 CFU/g respectively. E. coli loads were significantly reduced (2.45 to 3.97 log), whereas Cyclospora sporulation was not affected by this treatment.

Novel Chemical Processes: Ozone, Supercritical CO2, Electrolyzed Oxidizing Water, and Chlorine Dioxide Gas

The current need for minimally-processed foods with fresh-like, natural, and unadulterated qualities has increased the technological search for processes that ensure food safety while maintaining the food in a very wholesome taste-unaltered state. To that end, ozone, supercritical CO2, electrolyzed oxidizing water, and chlorine dioxide were chosen as emerging chemical technologies that hold much potential for ensuring food quality and safety standards. Some of these emerging antimicrobial technologies are briefly described.

Inactivation kinetics of inoculated Escherichia coli O157:H7, Listeria monocytogenes and Salmonella Poona on whole cantaloupe by chlorine dioxide gas

The objectives of this study were to examine inactivation kinetics of inoculated Escherichia coli O157:H7, Listeria monocytogenes and Salmonella Poona inoculated onto whole cantaloupe and treated with ClO(2) gas at different concentrations (0.5, 1.0, 1.5, 3.0 and 5.0 mg l(-1)) for different times (0, 2.0, 4.0, 6.0, 8.0 and 10.0 min). The effect of ClO(2) gas on the quality and shelf life of whole cantaloupe was also evaluated during storage at 22 degrees C for 12 days. A 100 microl inoculation of each targeted organism was spotted onto the surface (5 cm(2)) of cantaloupe rind (approximately 8-9 log CFU 5 cm(-2)) separately, air dried (60 min), and then treated with ClO(2) gas at 22 degrees C and 90-95% relative humidity for 10 min. Surviving bacterial populations on cantaloupe surfaces were determined using a membrane transferring method with a non-selective medium followed by a selective medium. The inactivation kinetics of E. coli O157:H7, L. monocytogenes and S. Poona were determined using nonlinear kinetics (Weibull model). A 3 log CFU reduction of E. coli O157:H7, L. monocytogenes and S. Poona were achieved with 5.0 mg l(-1) ClO(2) gas for 5.5, 4.2 and 1.5 min, respectively. A 5l og CFU reduction of S. Poona was achieved with 5.0 and 3.0 mg l(-1) ClO(2) gas for 6 and 8 min, respectively. A 4.6 and 4.3 log reduction was achieved after treatment with 5.0 mg l(-1) ClO(2) gas at 10 min for E. coli O157:H7 and L. monocytogenes, respectively. Treatment with 5.0 mg l(-1) ClO(2) gas significantly (p<0.05) reduced the initial microflora (mesophilic bacteria, psychrotrophic bacteria, and yeasts and molds) on cantaloupe by more than 2 log CFU cm(-2) and kept them significantly (p<0.05) lower than the untreated control during storage at 22 degrees C for 12 days. Treatment with ClO(2) gas did not significantly (p>0.05) affect the color of whole cantaloupe and extended the shelf life to 9 days compared to 3 days for the untreated control, when stored at ambient temperature (22 degrees C).

Identification of a non-pathogenic surrogate organism for chlorine dioxide (ClO2) gas treatment

The identification of non-pathogenic surrogate microorganisms is beneficial for determining and validating the efficacy of antimicrobial treatments in food manufacturing environments. A surrogate organism was identified to aid in the decontamination process of fresh produce when treated with chlorine dioxide (ClO(2)) gas. Thirty-two known strains of pathogenic and non-pathogenic microorganisms and seven unknown microbial isolates from mushroom, tomatoes, and strawberries were evaluated. The primary goal was to find alternative non-pathogenic organisms that had an equal or higher resistance compared to Escherichia coli O157:H7, Salmonella spp., and Listeria monocytogenes. Among the strains tested, MR1 (mushroom isolate), E. coli O157:H7 C7927, E. coli O157:H7 204P, STB2 (strawberry isolate), and vegetative cells of Bacillus cereus 232 in wet inoculum were found to be the most resistant to gaseous ClO(2) treatment at 0.3 mg/l for 1 min and D-values at 0.3 mg/l ClO(2) were 3.53, 1.95, 1.72, 1.68, and 1.57 min, respectively. For identification, the MR1 and STB2 strains were identified using a Ribotyper with the EcoRI restriction enzyme of 16S rDNA sequence. MR1 was identified as Hafnia alvei with a similarity value of 94% using the ribotype pattern and with a 93.6% similarity using an API 20E strip, and with a 99% similarity using 16S rDNA analysis. The Ped-2E9-based cytotoxicity assay was conducted for the MRI strain extracellular toxin and whole cell toxicity and did not show cytotoxicity. Analysis, using multiplex PCR, was performed to verify absence of the eaeA gene. H. alvei is a suitable non-pathogenic surrogate, with higher resistance to ClO(2) gas compared to pathogens studied, that may be useful to establish optimum conditions of ClO(2) gas decontamination systems.

Food as a vehicle for transmission of Shiga toxin-producing Escherichia coli

Contaminated food continues to be the principal vehicle for transmission of Escherichia coli O157:H7 and other Shiga toxin-producing E. coli (STEC) to humans. A large number of foods, including those associated with outbreaks (alfalfa sprouts, fresh produce, beef, and unpasteurized juices), have been the focus of intensive research studies in the past few years (2003 to 2006) to assess the prevalence and identify effective intervention and inactivation treatments for these pathogens. Recent analyses of retail foods in the United States revealed E. coli O157:H7 was present in 1.5% of alfalfa sprouts and 0.17% of ground beef but not in some other foods examined. Differences in virulence patterns (presence of both stx1 and stx2 genes versus one stx gene) have been observed among isolates from beef samples obtained at the processing plant compared with retail outlets. Research has continued to examine survival and growth of STEC in foods, with several models being developed to predict the behavior of the pathogen under a wide range of environmental conditions. In an effort to develop effective strategies to minimize contamination, several influential factors are being addressed, including elucidating the underlying mechanism for attachment and penetration of STEC into foods and determining the role of handling practices and processing operations on cross-contamination between foods. Reports of some alternative nonthermal processing treatments (high pressure, pulsed-electric field, ionizing radiation, UV radiation, and ultrasound) indicate potential for inactivating STEC with minimal alteration to sensory and nutrient characteristics. Antimicrobials (e.g., organic acids, oxidizing agents, cetylpyridinium chloride, bacteriocins, acidified sodium chlorite, natural extracts) have varying degrees of efficacy as preservatives or sanitizing agents on produce, meat, and unpasteurized juices. Multiple-hurdle or sequential intervention treatments have the greatest potential to minimize transmission of STEC in foods.

Applications of Chlorine Dioxide Gas for Control of Bacterial Soft Rot in Tomatoes

Chlorine dioxide (ClO₂) gas was generated from a mixture of sodium chlorite and ferric chloride plus water (impregnated into zeolite) in a Tyvek sachet over a 2- or 24-h period. The gas was distributed by a fan over wound-inoculated tomato fruit (Lycopersicon esculentum) enclosed in a sealed aluminum pressure cooker. Within 24 h of inoculation with 6 log₁₀ CFU of Erwinia carotovora subsp. carotovora per wound and storage at 22 to 24°C, bacterial soft rot was observed on >80% of the nontreated wounds (10 wounds/fruit and 4 or 6 fruit/treatment). By contrast, wounds that had been exposed to an atmosphere containing up to 99 mg ClO₂ during a 2- or 24-h period remained firm and dry with no evidence of bacterial activity or soft rot. After 72 h of incubation, wounds exposed to 88 mg ClO₂ produced over 24 h or 99 mg ClO₂ produced over 2 h were free of decay, whereas bacterial soft rot was observed in ca. 12% and less than 5% of wounds treated with 0.75 mg or 7.5 mg, respectively, for either 2 or 24 h. Wounds that had not been inoculated remained free of bacterial soft rot throughout the entire storage period. Wounds exposed to the highest doses of ClO₂, 88 mg/24 h or 99 mg/2 h, became bleached and sunken. Additionally, the stem scars on these fruit became cracked, sunken, and bleached. The intact cuticle was not visibly affected, and there was no observed change in overall fruit color. ClO₂ gas may be effective for controlling postharvest decays of fruit that have been inoculated prior to or during harvest.