ClO2 Gas Research Articles

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.

Low-cost, Small-scale Decontamination of Laboratory Equipment by Using Chlorine Dioxide Gas

A significant concern in laboratory animal medicine is contamination due to pathogen outbreaks and how to adequately decontaminate small equipment. Many factors play a role in the selection of the decontamination method including cost, efficacy, personnel time and safety. Chlorine dioxide (ClO₂) gas is an effective method, but decontamination often requires a ClO₂ gas generator with a specialized air-tight exposure chamber. Although this method works well for large-scale decon- tamination, the use of a gas generator may be impractical and too costly for smaller-scale decontamination. The goal of this study was to create and validate an effective, small-scale decontamination method that uses ClO₂ gas and which is an affordable, efficient, safe, and reproducible. First, we identified a product that generates ClO₂ gas after the combination of 2 dry reagents. To find an affordable exposure chamber, we evaluated the ability of 4 household totes with gasket-seal lid systems to retain ClO₂ gas and relative humidity (RH). The efficacy of decontamination was validated by concurrently using 2 different biologic indicators (BI), Bacillus atrophaeus (B.a.) and Geobacillus stearothermophilus (G.s.). All household totes evaluated held sufficient gas and RH for a 15-h cycle, providing adequate contact time to inactivate both BI evaluated. Our results suggest that a total exposure dose of 71 ± 42 ppm-h of ClO₂ gas over 15 h at 90% or greater RH is adequate to inactivate both B.a. and G.s. There was no statistical significance between the 2 BI as indicators for decontamination; 65 of 230 (28.3%) B.a. and 75 of 230 (32.6%) G.s spore strips were positive for growth (P = 0.36). In conclusion, we successfully combined a variety of low-cost materials to establish an effective, small-scale method to decontaminate laboratory equipment. Depending on the size of the tote and whether BI are used, the cost of our method is roughly 1% that of large-scale ClO₂ gas generators used with specialized air-tight exposure chambers.

Antimicrobial activity of gaseous chlorine dioxide against Aspergillus flavus on green coffee beans

The aim of this study was to use chlorine dioxide (ClO2) gas to inactivate Aspergillus flavus on green coffee beans. Green coffee beans inoculated with A. flavus were exposed to ClO2 gas generated from 0.75, 1, 1.25, or 1.5 mL of ClO2 solution in a sealed container at 25 or 50 °C (100% relative humidity [RH]) for up to 10 h. Numbers of A. flavus on beans treated at 25 °C decreased by 1.1–2.2 log cfu/bean within 1 h of exposure to ClO2 and decreased to below the detection limit (≤1.0 log cfu/bean) at all ClO2 concentrations after 10 h. At 50 °C, the microbial population reached the detection limit within 0.5 h regardless of the ClO2 solution concentration. Beans exposed to gas for 10 h at 25 °C were stored for 14 days under conditions of 43, 75, or 100% RH and 4, 12, or 25 °C. At 4 °C, visible mold growth was not established regardless of RH. After 12 days, mold was observed only at 25 °C. At 100% RH, beans stored under the same conditions without ClO2 gas treatment showed mold formation at 13 and 4 days at 12 and 25 °C, respectively.

Feasibility and efficacy of using gaseous chlorine dioxide generated by sodium chlorite-acid reaction for decontamination of foodborne pathogens on produce

The objective of this study was to evaluate the feasibility and efficacy of using chlorine dioxide (ClO2) gas generated by dry media (sodium chlorite and ferric chloride) and sodium chlorite-hydrogen chloride dosing methods for decontamination of foodborne pathogens on produce. Tomatoes, blueberries, and baby-cut carrots inoculated with Shiga toxin-producing Escherichia coli, Salmonella, and Listeria monocytogenes were treated with ClO2 gas in a pilot-scale decontamination process. The effects of cumulative ClO2 exposure, i.e., ClO2 concentration (ppm) × treatment time (h) (ppm-h), on the reductions of inoculated pathogens were determined. Results showed that the increase of cumulative ClO2 exposure between 300 and 1900 ppm-h increased the log reductions of pathogens on produce, whereas no significant increase in log reductions was observed after 1900 ppm-h. The cumulative ClO2 exposures of 300, 1300, and 1600 ppm-h caused >4.0-log CFU/g reductions of the pathogens on baby-cut carrots, tomatoes, and blueberries, respectively. The treatment was most effective against the pathogens on baby-cut carrots, likely due to the moisture on the surface of the peeled carrots. This study showed that the two ClO2 generation methods are suitable and effective for decontamination of produce. The correlation between the cumulative ppm-h and pathogen reduction was independent of the quantity of products and other factors that may affect the consumption rate of ClO2. Therefore, the treatment parameters obtained from this study can be used for decontamination applications of similar scale or as references for evaluating using ClO2 gas for decontamination of tomatoes, blueberries, and baby-cut carrots in commercial-scale trials.

CFD simulation for designing a chlorine gaseous sanitizer treatment system

A 3D numerical model using COMSOL software was developed to simulate the profile of ClO2 gas concentration and bacterial inactivation in treatment chambers with different gas inlets and outlets. The multiphysics simulation based on a finite element method (FEM) included compressible flow, convection and diffusion, and especially, pathogen inactivation codes using Java language were embedded into the program. Finally, each component of the model was coupled and simulated in a transient state. The main fluid stream reached a steady state in a short time because the input speed of ClO2 gas was fast compared to the size of the chamber. Though the chamber was a closed system, compressible air was not observed inside the chamber. Various scenarios with different gas inlet and outlet locations can influence the uniformity profile of increasing ClO2 gas concentration and bacterial inactivation. The optimal configuration was finally found by means of the simulation, and there was a good correspondence in pathogen inactivation profiles between CFD simulation and experiment. This study revealed the computational fluid dynamics (CFD) codes which can help the food processing industry in constructing a scaled-up system and establishing optimum sanitizing treatment conditions.

Chlorine Dioxide Generation Method and Its Action Mechanism for Removing Harmful Substances and Maintaining Quality Attributes of Agricultural Products

Agricultural products are perishable and easily contaminated by spoilage microorganisms or foodborne pathogens, causing decay of food and illness in consumers. Chlorine dioxide (ClO2) has many advantages as a fungicide in comparison to chlorine, NaClO, and ozone, and it can be used for sterilization and preservation due to its strong oxidizing properties. ClO2 gas is more widely used in food safety and food preservation than its aqueous solutions. However, the ClO2 gas produced on a large scale from a chemical reactor cannot be applied to food in small packages. Several recent reports have discussed the use of ClO2 self-releasing packaging. This article highlights the systematic evaluation of the performance of ClO2 alone and in combination with other treatments, such as 1-MCP, chitosan, and UV irradiation, in maintaining food safety and freshness of agricultural products. This article also focuses on the biological functions and mechanisms of ClO2-mediated preservation of plant or animal food, including damage to the cell wall and the membrane of pathogens, inhibition of ethylene biosynthesis, restoration of redox balance, and change of the compound structure of toxins, such as pesticides, insecticides, and mycotoxins.

In Vitro and In Vivo Inhibitory Effects of Gaseous Chlorine Dioxide Against Diaporthe batatas Isolated from Stored Sweetpotato.

Chlorine dioxide (ClO2) can be used as an alternative disinfectant for controlling fungal contamination during postharvest storage. In this study, we tested the in vitro and in vivo inhibitory effects of gaseous ClO2 against Diaporthe batatas SP-d1, the causal agent of sweetpotato dry rot. In in vitro tests, spore suspensions of SP-d1 spread on acidified potato dextrose agar were treated with various ClO2 concentrations (1–20 ppm) for 0–60 min. Fungal growth was significantly inhibited at 1 ppm of ClO2 treatment for 30 min, and completely inhibited at 20 ppm. In in vivo tests, spore suspensions were drop-inoculated onto sweetpotato slices, followed by ClO2 treatment with different concentrations and durations. Lesion diameters were not significantly different between the tested ClO2 concentrations; however, lesion diameters significantly decreased upon increasing the exposure time. Similarly, fungal populations decreased at the tested ClO2 concentrations over time. However, the sliced tissue itself hardened after 60-min ClO2 treatments, especially at 20 ppm of ClO2. When sweetpotato roots were dip-inoculated in spore suspensions for 10 min prior to treatment with 20 and 40 ppm of ClO2 for 0–60 min, fungal populations decreased with increasing ClO2 concentrations. Taken together, these results showed that gaseous ClO2 could significantly inhibit D. batatas growth and dry rot development in sweetpotato. Overall, gaseous ClO2 could be used to control this fungal disease during the postharvest storage of sweetpotato.

Slow-release chlorine dioxide gas treatment as a means to reduce Salmonella contamination on spices

Abstract Salmonella enterica is a major food safety issue for the spice industry. Slow-releasing chlorine dioxide (ClO2) gas from self-contained sachets, which can be employed in a small-scale operation, was evaluated for its effectiveness in reducing Salmonella contamination on black pepper, cumin, and sesame seed. Three levels of chlorine dioxide gas (100, 200, or 500 mg ClO2/kg spice) were applied to Salmonella-inoculated spices. Spices were sampled immediately after treatment, and at 1, 10, and 30-days post-treatment. The combined effect of ClO2 gas treatment and storage time on Salmonella numbers on spices was evaluated. Salmonella reductions on black pepper, cumin, and sesame seed samples ranged from 0.81 to 2.74 log CFU/g after ClO2 treatment. Storage time also had a significant impact on Salmonella numbers, as numbers decreased by up to 2.50 log CFU/g over 30 days of storage. Self-contained ClO2 releasing sachets could provide small food processors a post-lethality treatment alternative for spices.

Changes in Lipid Oxidation and Taste Compounds of Chicken Breast Meat by Slow-released ClO2 Gas Gel-pack during Storage

Changes in Lipid Oxidation and Taste Compounds of Chicken Breast Meat by Slow-released ClO2 Gas Gel-pack during Storage

Polymeric Films Containing Sodium Chlorite That Release Disinfectant Gas upon Activation with UV Light

AbstractPolymeric films that release disinfectant gas on demand have the potential to be useful for management of microbial burden (e.g., sterilization). Past attempts to create such films, however, have suffered from the need for stringent control over moisture or exposure to visible light prior to use. It is reported that polyvinyl alcohol (PVA) or polyolefin (POD) films that contain NaClO2 crystals can release ClO2 gas upon UV‐activation and exposure to moisture. In addition to showing that the concentration of gaseous ClO2 released from the polymeric films is sufficiently high for antimicrobial activity, fundamental insights into factors controlling ClO2 release are provided by using atomic force microscopy, optical microscopy, Raman microscopy, and time‐of‐flight secondary ion mass spectrometry. Specifically, by determining the sizes of the polymer‐dispersed NaClO2 particles, support for the hypothesis that UV light activates an interfacial layer of the NaClO2 crystals to generate ClO2 is obtained. Additionally, it is found that the half‐life of the UV‐activated state of NaClO2 depends on the reactivity of the polymer matrix. Because both PVA and POD possess properties analogous to polymers used in packaging films, it is concluded that the approach described in this study may enable introduction of deodorizing or antimicrobial functional properties into polymeric packaging.

Response of storage insect species to ClO2 fumigation conditions

Insects damage grain during post-harvest storage. Grain loss during storage is a serious problem, especially in less-developed countries. In this study, a gaseous ClO2 treatment was applied to four different insect species known to damage stored grains: Sitophilus zeamais (Motschulsky), Trogoderma granarium (Everts), Callosobruchus chinensis (Linnaeus), and Tribolium castaneum (Herbst). Different insect species showed different sensitivities to the same ClO2 fumigation conditions. The 100 ppm treatment level with 24 h exposure is effective to controlling S. zeamais, T. granarium, and C. chinensis. However, to control T. castaneum, a higher concentration of the ClO2 gas or increased exposure time is needed. The 200 ppm treatment level with 48 h exposure is effective to controlling T. castaneum.

Growth Inhibitory Effects of Chlorine Dioxide on Bacteria

Chlorine dioxide (ClO2) gas is a neutral chlorine compound. ClO2 gas was proven to effectively decontaminate different environments, such as hospital rooms, ambulances, biosafety level 3 laboratories, and cafeterias. In this study, to evaluate the effects of ClO2 gas, bacteria of clinical importance were applied. Staphylococci, Streptococci and Bacillus strains were applied and Klebsiella, and others e.g., Escherichia coli, Shigella, Salmonella, Serratia were also done for the inhibitory analysis. Bacteria plates were applied with a hygiene stick, namely, “FarmeTok (Medistick/Puristic)” to produce ClO2. ClO2-releasing hygiene stick showed the very strong inhibition of bacterial growth but had different inhibitions to the bacteria above 96.7% except for MRSA of 90% inhibition. It is difficult to explain why the MRSA were not inhibited less than others at this point. It can be only suggested that more releasing ClO2 should be essential to kill or inhibit the MRSA. B. subtilis, S. agalactiae, S. pyogenes, E. coli O157:H7, S. typhi (S. enterica serotype typhi) and S. marcesence were inhibited over 99%. This study will provide fundamental data to research growth inhibition by ClO2 gas with bacteria of clinical importance value.

Gas-Phase Chemistry of the NO–SO2–ClO2 System Applied to Flue Gas Cleaning

The chemical interactions that occur between NO, SO2, and ClO2 are investigated. In focus is the oxidation of NO with gaseous ClO2 for simultaneous removal of NOx and SOx from combustion-derived flue gases. Laboratory-scale experiments were conducted to examine the conversion of NO to NO2, under the following conditions: temperature range of 100–180 °C; H2O concentrations in the range of 0%–25%; ClO2–NO molar ratios in the range of 0.2–0.6; and NO and SO2 flue gas concentrations in the ranges of 0–250 ppm and 0–1000 ppm, respectively. The results show that NO is oxidized efficiently by ClO2, whereas the ClO2–SO2 reactions are insignificant. The water concentration had no effect on oxidation, and the temperature had a limited effect, within the investigated ranges. The outcomes favor the process economics of the studied application, since ClO2 consumption is negligible with respect to SO2 oxidation.

Gaseous chlorine dioxide maintained the sensory and nutritional quality of grape tomatoes and reduced populations of Salmonella enterica serovar Typhimurium

There have been numerous reports on the effectiveness of gaseous chlorine dioxide (gClO2) in inactivating various human pathogens associated with fresh produce. However, studies dealing with both microbial reduction and impact on quality and nutrients of tomatoes are scarce. In the present study, gaseous chlorine dioxide was evaluated for its effectiveness on populations of Salmonella and native microorganisms on grape tomatoes, and impacts on sensory and nutritional quality. Grape tomatoes, dip inoculated with a cocktail of Salmonella enterica serovar Typhimurium, were treated with three different levels of gClO2 generated by sachets containing sodium chlorite and reducing acids for up to 5 h in 20-L chambers. For the quality study, non-inoculated fruits were treated similarly with the gClO2, and stored for 21 d at 10 °C. Sensory and nutritional quality, and native microflora were measured at 1, 7, 14 and 21 d of storage. Headspace gClO2 concentrations and humidity in the chambers were measured during the treatments. Concentrations of gClO2 in the chamber were relatively stable during the 2.5 and 5 h treatment times. Gaseous ClO2 at 1.9 mg/L for 5 h and 4.3 mg/L for 2.5 and 5 h reduced Salmonella populations from 5.4 log CFU/fruit to a non-detectable level (detection limit 1.70 log CFU/fruit). However, populations of native microflora were not consistently affected by the gClO2 treatments. Furthermore, the treatments did not have any significant effect on appearance, off-odor, firmness, color, or lycopene, and vitamin C contents of grape tomatoes during the 21-d storage. Overall, gClO2 treatments that achieved more than 4 log reductions of Salmonella did not significantly (P > 0.05) affect sensory or nutritional quality of grape tomatoes.

Effect of Chlorine Dioxide Gas Application to Egg Surface: Microbial Reduction Effect, Quality of Eggs, and Hatchability.

Controlling of microorganisms in the industrial process is important for production and distribution of hatching and table eggs. In the previous study, we reported that chlorine dioxide (ClO2) gas of a proper concentration and humidity can significantly reduce the load of Salmonella spp. on eggshells. In this study, we compared microbial reduction efficacy on egg’s surface using hatching eggs and table eggs, internal quality of table eggs, and hatchability after both the conventional method (washing and UV expose, fumigation with formalin) and ClO2 gas disinfection. Application of 40 ppm ClO2 gas to the table and hatching eggs, respectively, reduced the aerobic plate count (APC) with no statistical difference compared with the conventional methods. Additionally, we didn’t observed that any significant difference in albumin height, Haugh unit (HU), and yolk color, this result confirms that 40 ppm ClO2 had no effect on the internal quality of the table eggs, when comparing with the UV treatment method. The hatchability of hatching eggs was not statistical different between formaldehyde fumigation and 80 ppm ClO2 gas treatment, though the value was decreased at high concentration of 160 ppm ClO2 gas. From these results, we recommend that ClO2 gas can be used as a safe disinfectant to effectively control egg surface microorganisms without affecting egg quality.

Moisture-triggered release of self-produced ClO2 gas from microcapsule antibacterial film system

In this study, a novel chlorine dioxide (ClO2) microcapsule with a performance of moisture-triggered release was fabricated followed by the mixing with polylactic acid (PLA) for the preparation of an antibacterial packaging film. ClO2 microcapsules were first prepared by encapsulating stable ClO2 solution (NaClO2 as the main component) in a PLA shell, and the resulting microcapsules together with tartaric acid were applied as antibacterial components for antimicrobial PLA film using solvent casting method. The impact of ClO2 microcapsules on the antimicrobial effectiveness, oxygen and water vapor barrier properties, mechanical behavior, and thermal stability of PLA films was investigated. The results showed that the addition of ClO2 microcapsules at a concentration of 20% imparted PLA films excellent antimicrobial properties with a growth inhibition of Escherichia coli and Staphylococcus aureus by 4.95 log CFU/mL and the antibacterial rate was 99%. Furthermore, the tensile strength of the films with ClO2 microcapsules at a concentration of 20% was 21.20 MPa, which was 19% higher than that of the PLA film without microcapsules. The oxygen and water vapor transmission rates reached 2800 cm3 m−2 24 h−1 and 20.00 g m−2 24 h−1, respectively, and the barrier properties were improved by 20 and 36.14%. Thermogravimetric analysis showed that the generated film was stable before 193 °C. Scanning electron microscopy analysis confirmed a good compatibility between the ClO2 microcapsules and the PLA matrix, and the emerged voids indicated the generation of ClO2 and its release from the antimicrobial film. An obvious sustained release of ClO2 from the antimicrobial film completed until 240 h. The release behavior fitted the logistic model, and the release mechanism followed the S model. This study may provide a feasible approach for the development of food packaging materials with efficient antibacterial activity and sustained-release performance.

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

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 gaseous chlorine dioxide (ClO2 ) with different concentrations and numbers of treatments on controlling berry decay and rachis browning of table grape

Chlorine dioxide (ClO2) gas was used to control berry decay and rachis browning of table grape due to its antimicrobial and anti-browning properties. It was proposed that if ClO2 gas is fully absorbed by the fruit, the maximum total ClO2 dose can be calculated based on the maximum allowable residual concentration. To avoid possible bleaching effects on grape peel from high concentrations of ClO2, the total amount of ClO2 gas needs to be injected into the packages in many small doses at specific time intervals over the course of the 90-day storage period. Spoilage microorganism counts, decay rate, electrolyte leakage, rachis browning and residual ClO2 in berry were investigated. The results showed that ClO2 treatment could significantly reduce berry decay and rachis browning (p ≤ .05) compared to the control. Grape treated with 1.0 mg L−1 ClO2 6 times at 15-day intervals maintained better fruit quality without any risks from the residual ClO2. Practical applications The present research found that ClO2 treatment is useful for improving the microbial safety of grapes and reducing berry decay and rachis browning during storage, and low doses of ClO2 spread over many treatment can yield better results.

Novel generation systems of gaseous chlorine dioxide for Salmonella inactivation on fresh tomato

Chlorine dioxide (ClO2) is an antimicrobial agent used in fresh produce sanitation to inactivate a board range of pathogens. Compared to its aqueous form, gaseous ClO2 has a stronger penetrating ability and therefore a greater inactivation effect. A novel ClO2(g) generating method utilizes carbon dioxide and moisture naturally released from tomato during respiration to react with NaClO2 for ClO2(g) generation has been proposed in our previous study. This study further developed two novel generation systems (i.e., electrospun fiber and releasing film) for the method applications in reality. In this study, the physical properties (i.e., viscosity, conductivity, pH and surface tension) of different poly-ethylene oxide (PEO) polymer solutions (i.e., 2%, 3%, 4% PEO and 3% PEO with 0.15%, 0.3% NaClO2), the morphology and diameter distribution of electrospun fibers produced as well as the loading efficiency of NaClO2 onto the fibers were investigated. The successful generation of ClO2(g) from the two developed systems were observed. Four log CFU Salmonella/fruit inoculated on the surface were significantly reduced (p < 0.05) to undetectable level (<5 CFU/fruit) within 2 days under both systems and the surface color and firmness of the fruits were not impacted (p > 0.05) during the entire storage period (14 days for 10 °C and 7 days for 22 °C). The information can be utilized for Salmonella safety enhancement on fresh tomato during storage, transportation and retail stages. It also provides insights for the further applications of the generating method on many other fresh produce as well as on many other pathogens.

Inactivation of foodborne pathogens on fresh produce by combined treatment with UV-C radiation and chlorine dioxide gas, and mechanisms of synergistic inactivation

This study was conducted to evaluate the antimicrobial effect of the combined treatment of UV-C radiation (UVC) and chlorine dioxide (ClO2) gas against Escherichia coli O157:H7, Salmonella Typhimurium, and Listeria monocytogenes on spinach leaves and tomato surfaces and to clarify the mechanisms of the synergistic effect of this combined treatment. In the case of spinach leaves, as treatment time increased the combined treatments of UVC and ClO2 gas showed additive effects: the total microbial inactivation of the combined treatment was not significantly (p > 0.05) different from the sum of individual treatments. On tomatoes, synergistic effects in inactivating E. coli O157:H7 and S. Typhimurium were observed after combination treatment of UVC and ClO2 gas (10 ppmv) for 15 min or more. For both pathogens, inactivation achieved with the combination treatment was significantly (p < 0.05) higher than the sum of UVC and ClO2 gas (10 ppmv) inactivation. In the case of L. monocytogenes, the synergistic effect was observed after the combination treatment of UVC and ClO2 gas (10 ppmv) for 20 min. Measuring leakage of UV-absorbing substances and analyzing transmission electron microscopy images provide evidence that damage to the cell membrane and changes to membrane permeability are involved in the synergistic lethal effect of the combination treatment of UVC and ClO2 gas. Combined treatment of UVC and ClO2 gas (10 ppmv) did not significantly (p > 0.05) affect the color and texture of samples during 7 days of storage.