Effect of Chlorine Dioxide Gas onSalmonella entericaInoculated on Navel Orange Surfaces and Its Impact on the Quality Attributes of Treated Oranges

Generation, mechanisms, kinetics, and effects of gaseous chlorine dioxide in food preservation

Food preservation is a critical issue in ensuring food safety and quality. Growing concern around industrial pollution of food and demand for environmentally sustainable food has led to increased interest in developing effective and eco-friendly preservation techniques. Gaseous ClO2 has gained attention for its strong oxidizing properties, high efficacy in microorganism inactivation, and potential for preserving the attributes and nutritional quality of fresh food while avoiding the formation of toxic byproducts or unacceptable levels of residues. However, the widespread use of gaseous ClO2 in the food industry is limited by several challenges. These include large-scale generation, high cost and environmental considerations, a lack of understanding of its mechanism of action, and the need for mathematical models to predict inactivation kinetics. This review aims to provide an overview of the up-to-date research and application of gaseous ClO2 . It covers preparation methods, preservation mechanisms, and kinetic models that predict the sterilizing efficacy of gaseous ClO2 under different conditions. The impacts of gaseous ClO2 on the quality attributes of fresh produce and low-moisture foods, such as seeds, sprouts, and spices, are also summarized. Overall, gaseous ClO2 is a promising preservation approach, and future studies are needed to address the challenges in large-scale generation and environmental considerations and to develop standardized protocols and databases for safe and effective use in the food industry.

Inactivation of Foodborne Pathogen Biofilm Cells Using a Combination Treatment with Gaseous Chlorine Dioxide and Aerosolized Sanitizers

A biofilm is a three-dimensional microbial community, which is difficult to completely control with a typical sanitizer owing to its complex structure. The aim of this study was to establish a system for the combined treatment of biofilms with 10 ppmv gaseous chlorine dioxide (ClO2) and antimicrobial agents (2% citric acid, 2% hydrogen peroxide [H2O2], and 100 ppm peracetic acid [PAA]), and to investigate the synergistic microbicidal efficacy of the combination treatments to inactivate Listeria monocytogenes, Salmonella Typhimurium, and Escherichia coli O157:H7 in biofilms. The antimicrobial agents were aerosolized using a humidifier on top of a chamber to achieve a relative humidity of 90% (within a range of ±2%). While biofilm treatment with the aerosolized antimicrobial agents for 20 min inactivated approximately 1 log CFU/cm2 (0.72-1.26 log CFU/cm2) of the pathogens and the gaseous ClO2 gas treatment for 20 min inactivated <3 log CFU/cm2 (2.19-2.77 log CFU/cm2), combination treatment with citric acid, H2O2, and PAA for 20 min achieved microbial reductions of 2.71-3.79, 4.56-5.12, and 4.45-4.67 log CFU/cm2, respectively. Our study demonstrates that foodborne pathogens in biofilms can be inactivated by combining gaseous ClO2 treatment with aerosolized antimicrobial agents. The results of this study provide baseline data for the food industry to help control foodborne pathogens in biofilms on inaccessible surfaces.

Chlorine dioxide gas mediated inactivation of the biofilm cells of

This study evaluated the chlorine dioxide (ClO2) gas mediated inactivation of the biofilm cells of foodborne pathogens on food contact surfaces. Biofilm cells of Escherichia coli O157:H7, Salmonella Typhimurium, and Listeria monocytogenes were developed on stainless steel (SS) and high density polyethylene (HDPE) coupon surfaces, and 5-day-old biofilms were treated with ClO2 gas at 60 and 90% relative humidity (RH) for up to 20 min. With an increase in gas concentration and treatment time, significant differences (p < 0.05) were observed between reduction levels under different RH conditions. Treatment with 50 ppmv of ClO2 gas (60% RH) for 20 min resulted in log reductions from 2.08 to 4.62 and 2.08 to 4.41 of the biofilm cells of three pathogens on SS and HDPE surfaces, respectively. The levels of biofilm cells of E. coli O157:H7, S. Typhimurium, and L. monocytogenes on SS and HDPE surfaces were reduced to below the detection limit (0.48 log CFU/cm2) within 15, 20, and 20 min, respectively, when exposure to 50 ppmv of ClO2 gas at 90% RH.

Validation of process technologies for enhancing the safety of low-moisture foods: A review

The outbreaks linked to foodborne illnesses in low-moisture foods are frequently reported due to the occurrence of pathogenic microorganisms such as Salmonella Spp. Bacillus cereus, Clostridium spp., Cronobacter sakazakii, Escherichia coli, and Staphylococcus aureus. The ability of the pathogens to withstand the dry conditions and to develop resistance to heat is regarded as the major concern for the food industry dealing with low-moisture foods. In this regard, the present review is aimed to discuss the importance and the use of novel thermal and nonthermal technologies such as radiofrequency, steam pasteurization, plasma, and gaseous technologies for decontamination of foodborne pathogens in low-moisture foods and their microbial inactivation mechanisms. The review also summarizes the various sources of contamination and the factors influencing the survival and thermal resistance of pathogenic microorganisms in low-moisture foods. The literature survey indicated that the nonthermal techniques such as CO₂ , high-pressure processing, and so on, may not offer effective microbial inactivation in low-moisture foods due to their insufficient moisture content. On the other hand, gases can penetrate deep inside the commodities and pores due to their higher diffusion properties and are regarded to have an advantage over thermal and other nonthermal processes. Further research is required to evaluate newer intervention strategies and combination treatments to enhance the microbial inactivation in low-moisture foods without significantly altering their organoleptic and nutritional quality.

Practical in-storage interventions to control foodborne pathogens on fresh produce

Although tremendous efforts have been made to ensure fresh produce safety, various foodborne outbreaks and recalls occur annually. Most of the current intervention strategies are evaluated within a short timeframe (less than 1 h), leaving the behavior of the remaining pathogens unknown during subsequent storages. This review summarized outbreak and recall surveillance data from 2009 to 2018 obtained from government agencies in the United States to identify major safety concerns associated with fresh produce, discussed the postharvest handling of fresh produce and the limitations of current antimicrobial interventions, and reviewed the intervention strategies that have the potential to be applied in each storage stage at the commercial scale. One long-term (up to 12 months) prepacking storage (apples, pears, citrus among others) and three short-term (up to 3 months) postpacking storages were identified. During the prepacking storage, continuous application of gaseous ozone at low doses (≤1 ppm) is a feasible option. Proper concentration, adequate circulation, as well as excess gas destruction and ventilation systems are essential to commercial application. At the postpacking storage stages, continuous inhibition can be achieved through controlled release of gaseous chlorine dioxide in packaging, antimicrobial edible coatings, and biocontrol agents. During commercialization, factors that need to be taken into consideration include physicochemical properties of antimicrobials, impacts on fresh produce quality and sensory attributes, recontamination and cross-contamination, cost, and feasibility of large-scale production. To improve fresh produce safety and quality during storage, the collaboration between researchers and the fresh produce industry needs to be improved.

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.

In Vitro and In Vivo Inhibitory Effects of Gaseous Chlorine Dioxide against Fusarium oxysporum f. sp. batatas Isolated from Stored Sweetpotato: Study II

Chlorine dioxide (ClO₂) has been widely used as an effective disinfectant to control fungal contamination during postharvest crop storage. In this study, Fusarium oxysporum f. sp. batatas SP-f6 from the black rot symptom of sweetpotato was isolated and identified using phylogenetic analysis of elongation factor 1-α gene; we further examined the in vitro and in vivo inhibitory activities of ClO₂ gas against the fungus. In the in vitro medium tests, fungal population was significantly inhibited upon increasing the concentration and exposure time. In in vivo tests, spore suspensions were drop-inoculated onto sweetpotato slices, followed by treatment using various ClO₂ concentrations and treatment times to assess fungus-induced disease development in the slices. Lesion diameters decreased at the tested ClO₂ concentrations over time. When sweetpotato roots were dip-inoculated in spore suspensions prior to treatment with 20 and 40 ppm of ClO₂ for 0-60 min, fungal populations significantly decreased at the tested concentrations for 30-60 min. Taken together, these results showed that ClO₂ gas can effectively inhibit fungal growth and disease development caused by F. oxysporum f. sp. batatas on sweetpotato. Therefore, ClO₂ gas may be used as a sanitizer to control this fungus during postharvest storage of sweetpotato.

Effect of temperature on chlorine dioxide inactivation of Escherichia coli O157:H7, Salmonella typhimurium, and Listeria monocytogenes on spinach, tomatoes, stainless steel, and glass surfaces

The objective of this study was to evaluate how treatment temperature influences the solubility of ClO₂ gas and the antimicrobial effect of ClO₂ gas against Escherichia coli O157:H7, Salmonella Typhimurium, and Listeria monocytogenes on produce and food contact surfaces. Produce and food contact surfaces inoculated with a combined culture cocktail of three strains each of the three foodborne pathogens were processed in a treatment chamber with 20 ppmv ClO₂ gas at 15 or 25 °C under the same conditions of absolute humidity (11.2-12.3 g/m³) for up to 30 min. As treatment time increased, ClO₂ gas treatment at 15 °C caused significantly more (p < 0.05) inactivation of the three pathogens than treatment at 25 °C. ClO₂ gas treatment at 25 °C for 30 min resulted in 1.15 to 1.54, 1.53 to 1.88, and 1.00 to 1.78 log reductions of the three pathogens on spinach leaves, tomatoes, and stainless steel No.4, respectively. ClO₂ gas treatment at 15 °C for 30 min caused 2.53 to 2.88, 2.82 to 3.23, and 2.37 to 3.03 log reductions of the three pathogens on spinach leaves, tomatoes, and stainless steel No.4, respectively. Treatment with ClO₂ gas at 25 °C for 20 min resulted in 1.88 to 2.31 log reductions of the three pathogens on glass while >5.91 to 6.82 log reductions of these pathogens occurred after 20 min when treated at 15 °C. Residual ClO₂ levels after gas treatment at 15 °C were significantly (p < 0.05) higher than those at 25 °C. The results of this study can help the food processing industry establish optimum ClO₂ gas treatment conditions for maximizing the antimicrobial efficacy of ClO₂ gas.

Effect of relative humidity on inactivation of foodborne pathogens using chlorine dioxide gas and its residues on tomatoes

The effect of relative humidity (RH) on the antimicrobial efficacy of chlorine dioxide (ClO₂ ) gas against foodborne pathogens on tomatoes was evaluated. Also, levels of ClO₂ residues on tomatoes after exposure to ClO₂ gas under different RH conditions were measured to determine the quantity of solubilized ClO₂ gas on tomato surfaces. Escherichia coli O157:H7, Salmonella Typhimurium and Listeria monocytogenes were inoculated on tomatoes and exposed to ClO₂ gas (5, 10, 20 and 30 ppmv) under different RH conditions (50, 70 and 90%). As ClO₂ gas concentration and treatment time increased, significant differences (P < 0·05) were observed between inactivation levels under different RH conditions. Exposure to 30 ppmv of ClO₂ gas (50% RH) for 20 min resulted in 1·22-1·52 log reductions of the three foodborne pathogens. Levels of the three foodborne pathogens were reduced to below the detection limit (0·48 log CFU per cm² ) within 15 min when exposed to 30 ppmv of ClO₂ gas at 70% RH and within 10 min at 90% RH. At a given ClO₂ gas concentration, ClO₂ residues on tomatoes significantly (P < 0·05) increased with increasing RH, and there were close correlations between log reductions of pathogens and ClO₂ residues on tomatoes.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study reported on the correlation between the amount of ClO₂ residues on produce surfaces and the level of inactivation of pathogens after ClO₂ gas treatment. Variations in RH have great effect on the solubilization of ClO₂ gas on tomato surfaces considering that ClO₂ residues on tomatoes increased with increasing RH. Also, the amount of ClO₂ residues on tomatoes is positively correlated with the level of inactivation of pathogens. The results of this study provide insights for predicting inactivation patterns of foodborne pathogens by ClO₂ gas for practical application by the fresh produce industry.

Effect of the use of a neutralizing step after antimicrobial application on microbial counts during challenge studies for orange disinfection

The effects of using a neutralizer after applying antimicrobial treatments and the effect of time lapse between treatment application and subsequent recovery and enumeration of Escherichia coli O157:H7 and Salmonella were investigated in Valencia oranges. Inoculated oranges surfaces were washed with distilled water for 15 s and then sprayed with a solution containing 200 mg/liter sodium hypochlorite (pH 6.5) for 15 s; they were then dipped in L-lactic acid (2.0% at 55°C) for 1 min or in distilled water at 80°C for 1 min. Posttreatment, oranges were divided into two groups. In the first group, oranges were dipped in neutralization treatment: 270 ml of buffered peptone water for 2 min for lactic acid-treated oranges, 270 ml of Dey-Engley broth for 2 min for chlorine-treated oranges, or 3.7 liters of tap water (25°C) for 10 s for hot water-treated oranges. The second group of treated oranges was not subjected to any neutralizer. All oranges then were kept at room temperature (average 26.2°C) and sampled at 0, 7.5, and 15 min for enumeration of surviving Salmonella and E. coli O157:H7. The orange surface (30 cm(2)) was excised for pathogen enumeration. The presence of free chlorine and changes in pH and temperature on the orange surface were determined in uninoculated, treated oranges. Free chlorine was detected on oranges after treatment; the change in temperature of orange surfaces was greater during treatment with hot water than with lactic acid. Nevertheless, pathogen enumeration did not show any impact of neutralizer use on the residual activity of antimicrobials or any impact of the time elapsed between antimicrobial treatment and recovery of bacterial pathogens from inoculated oranges (P ≥ 0.05). The results of this study indicate that the lack of a neutralizing step before enumeration of pathogens is not likely to affect the accuracy of results during challenge studies to test pathogen reduction strategies on oranges.

Comparison of different washing treatments for reducing pathogens on orange surfaces and for preventing the transfer of bacterial pathogens to fresh-squeezed orange juice

The objectives of this study were to compare the effectiveness of various washing treatments for reducing Escherichia coli O157:H7, Salmonella sp., and Listeria monocytogenes populations on orange surfaces and to measure the effect of some of these treatments in preventing the transfer of pathogens during juice extraction. Orange surfaces inoculated with L. monocytogenes or a mixture of E. coli O157:H7 and Salmonella Typhimurium were washed by water spray and then sprayed with or dipped in water at 80°C for 1 min, 70% ethanol for 15, 30, or 45 s or 1, 2, or 4 min, 2 or 4% lactic acid solution at 55°C for 15, 30, or 45 s or 1, 2, or 4 min, or 200 mg/liter hypochlorite at pH 6.5 or 10 for 15 s. The surviving populations of these pathogens on the oranges were enumerated after each treatment. In a further stage, the ability of these pathogens to be transferred to the juice during extraction was tested. Juice was obtained from inoculated oranges that were subjected to selected treatments using chlorine, lactic acid, ethanol, and hot water as described above, and then bacterial counts in orange juice were determined. The application of these treatments reduced the populations of pathogens on orange surfaces by 1.9 to >4.9 log, 1.9 to >4.6 log, and 1.4 to 3.1 log cycles for E. coli O157:H7, Salmonella Typhimurium, and L. monocytogenes, respectively. The treatments using hot water or lactic acid showed greater reductions than other treatments. The time, antimicrobial concentration, and form of application affected the bacterial reduction. All treatments resulted in undetectable counts in the juice. Nevertheless, pathogens were recovered by the enrichment-plating method. Treatment of oranges before juice extraction may reduce the risk associated with consuming orange juice.