ClO2 Gas Treatment Research Articles

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.

Inactivation of Salmonella Newport on blueberries by treatment with chlorine dioxide gas and its effect on blueberry qualities

The purpose of this study was to use chlorine dioxide (ClO2) gas to inactivate Salmonella Newport on blueberries and observe quality changes of blueberries as affected by the treatment. Blueberries inoculated with S. Newport were treated with ClO2 gas for 10 h ClO2 gas was generated from either 1 or 2 mL of ClO2 solution dropped in a sealed container and the container was hold at 12 °C or 25 °C. Within 30 min, Salmonella populations on blueberries treated with ClO2 gas, regardless of treatment temperature and amount of ClO2 solution, reduced below the detection limit (1.7 log CFU/sample) and the organism was eliminated within 30 min when 1 mL of ClO2 solution was used to generate gas at 25 °C. After the ClO2 gas treatment, blueberries were analyzed with an electronic eye. Color of untreated and ClO2-gas treated blueberries are composed of 12 and 11 color codes, respectively. Out of the color codes, 7 codes of both blueberries in control and treatment groups are the same. ClO2 gas treatment did not cause significant changes in Hunter's L, a, and b-value of blueberries. Hardness (g) of blueberries treated with ClO2 gas for 30 min significantly increased; however final values were not significantly different from the values of untreated ones. As a result of this study, the ClO2 gas successfully reduced S. Newport on blueberries without significant changes in their color and hardness.

Effects of chlorine dioxide gas fumigation on the storage quality of astringent persimmon (Diospyros kaki T.) Cheongdobansi

Because of their short harvest season, large quantities of persimmons must often be processed within a limited time. Therefore, new methods to extend their storage life are required. This study examined the effects of chlorine dioxide (ClO2) gas fumigation for various treatment periods on the storage quality of astringent persimmons Cheongdobansi under low-temperature conditions. The conditions consisted of continuous treatment with ClO2, treatment for 2 weeks with ClO2, and no treatment, all of which are stored at low temperatures. Control samples (storage 0 days) without any treatment were prepared and all experiments were conducted for 10 weeks at two-week intervals. The ClO2 gas treatment maintained the moisture content, color value, hardness, soluble tannin content, and sensory characteristics. However, ClO2 gas treatment did not affect the soluble solids, pH, and total sugar content. In particular, continuous treatment with ClO2 maintained the storage quality after 6-8 weeks of storage, particularly the hardness and weakness (sensory evaluation). The results suggest the potential of continuous treatment with ClO2 as a highly effective method for maintaining the freshness of Cheongdobansi.

Novel gaseous chlorine dioxide treatment system for improving the safety and quality of table grapes during cold storage

This study focused on the development of a gaseous ClO2 treatment system that contained dry ice that was used to form carbon dioxide (CO2) and an absorbent pad with sodium chlorite (NaClO2) solution for ClO2 gas generation. Furthermore, the effects of ClO2 gas on the populations of Listeria monocytogenes and the quality properties of table grapes during cold storage were evaluated. The system continuously released the sufficient concentrations of ClO2 gas to treat berries during 30 d of cold storage. After 20 h of ClO2 gas treatment, the populations of Listeria monocytogenes decreased from 5.88 log CFU/g to a non-detectable (ND) level. There were no significant (p > 0.05) changes in the color parameters (L*, a*, and b*) of table grapes treated with ClO2 gas. The firmness, weight, total soluble solids (TSS), and titratable acid (TA) losses of table grapes were significantly (p < 0.05) reduced by ClO2 gas, while Vitamin C was unaffected. Additionally, the residual ClO2 of table grapes were <0.5 mg/kg, which is considered a safe level. Overall, the novel gaseous ClO2 treatment system may be used as an effective intervention technology to improve the safety and quality of table grapes during cold storage.

Gaseous chlorine dioxide technology for improving microbial safety of spices

In this study, black peppercorns and cumin seeds were inoculated with a five-serotype cocktail of Salmonella or its surrogate Enterococcus faecium NRRL B-2354. The inoculated samples (ca. 107 CFU/g) were treated by ClO2 gas at different gas concentrations (5, 10, and 15 mg/L) and relative humidities (60, 70, and 80%) at room temperature (25 °C) at five gas exposure times (60, 120, 180, 240, 300 min). More than 5-log reduction of Salmonella was achieved in both spices with 300 min of ClO2 gas treatment at 15 mg/L and 80% RH. The corresponding values for E. faecium were 4.36 and 4.17 log CFU/g in black peppercorns and cumin seeds, respectively, which were significant lower than Salmonella (p < 0.05). Gas concentration, RH, and exposure time showed significantly positive linear associations with Salmonella inactivation. E. faecium appears a suitable surrogate for Salmonella and can be used for future process validations using comparable conditions.

Antimicrobial activity of ClO2 gas against Salmonella Enteritidis on almonds

Nuts, including almonds, are occasionally contaminated with Salmonella spp. In this study, we used chlorine dioxide (ClO2) gas to inactivate S. enterica subsp. Enterica serovar Enteritidis on almonds. Almonds inoculated with a single strain of S. Enteritidis (8.95 log cfu/mL) were exposed to ClO2 gas generated from 1.0 or 1.5 mL ClO2 solution in a sealed container at 50 or 60 °C (43% relative humidity) for up to 10 h. The concentration of ClO2 gas peaked at 354–510 and 750–786 ppm within 0.5 h upon deposition of 1.0 and 1.5 mL of aqueous ClO2, respectively, and gradually decreased thereafter. Population of S. Enteritidis on almonds treated at 50 °C decreased to 1.70–2.32 log cfu/sample within 1 h of exposure to ClO2 gas and decreased to below the detection limit (1.7 log cfu/sample) at all ClO2 concentrations after 8 h. At 60 °C, the microbial population fell below the detection limit within 1 h, regardless of the volume of ClO2 solution supplied. Microbial survival on almonds treated with ClO2 gas and stored at 12 or 25 °C was observed for up to 8 weeks and the organism was not recovered from the almonds treated for 10 h and stored at 12 °C for 2–8 weeks. The lightness (L value) and redness (a value) of almonds treated for 10 h were not changed by ClO2 gas treatment, but yellowness (b value) increased. Results showed that Salmonella on almonds was successfully inactivated by ClO2 gas treatment and the microbial survival did not occur during storage.

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.

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.

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.

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 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.

Bactericidal effects of chlorine dioxide gas against E. coli and S. Typhimurium in vitro

Chlorine dioxide gas is a relatively new sanitizer in the food industry that has more accessibility than its aqueous form. Depending on the method by which ClO2 gas is generated, there can be byproducts like chlorite and chlorate ions, which can decrease its disinfectant effect and purity. Recently, new technology that generates chlorine dioxide without using chlorine gas has been developed to remove those defects. This new electrochemical method generates gaseous chlorine dioxide from aqueous sodium chlorite (NaClO2). The present study was conducted to evaluate the effects of ClO2 gas generated by an electrochemical method against foodborne microorganisms. To accomplish this, ClO2 gas at different concentrations (1, 5, 10 and 20 ppm) was applied to E. coli and S. Typhimurium for different exposure times (1, 5, 10, 15 and 20 min) under room temperature conditions at <40% relative humidity. The results revealed ClO2 gas was highly effective for the inactivation of E. coli and S. Typhimurium and showed a reduction in populations of over 5 log CFU/ml under ambient conditions with low relative humidity (30-40%). In conclusion, ClO2 gas treatment is highly applicable to control of foodborne pathogens.

Inactivation of foodborne pathogens on alfalfa and radish seeds by sequential treatment with chlorine dioxide gas and dry heat

This study was conducted to evaluate the antimicrobial effect of sequential treatment with chlorine dioxide (ClO2) gas and dry heat against Escherichia coli O157:H7 and Salmonella Typhimurium on alfalfa and radish seeds. Inoculated alfalfa and radish seeds were treated with 150 ppmv of ClO2 gas for 1 h followed by 70 or 80 °C dry heat for 0, 1, 3 or 5 h. Dry heat treatment alone at 80 °C for 5 h resulted in 3.08 and 3.23 log reductions of E. coli O157:H7 and S. Typhimurium on alfalfa seeds, respectively. ClO2 gas treatment alone for 1 h resulted in 1.22–1.58 and 1.45 to 1.61 log reductions of E. coli O157:H7 and S. Typhimurium, respectively. Subsequent dry heat treatment (80 °C) for 5 h caused more than 5.32 and 5.29 log reduction of E. coli O157:H7 and S. Typhimurium, respectively. On radish seeds, dry heat treatment at 80 °C for 5 h resulted in 2.49 and 2.27 log reductions of E. coli O157:H7 and S. Typhimurium, respectively, and sequential treatment with ClO2 gas and dry heat (80 °C) for 5 h caused 4.38 and 4.11 log reduction of E. coli O157:H7 and S. Typhimurium, respectively. The germination rate of seeds did not significantly decrease after sequential treatment except for radish seeds sequentially treated with ClO2 gas and dry heat at 80 °C for 5 h.

Antimicrobial efficacy of gaseous chlorine dioxide against Salmonella enterica Typhimurium on grape tomato (Lycopersicon esculentum)

SummaryThe aim of this study was to investigate the effects of gas level and treatment condition on antimicrobial efficacy of ClO2 gas against Salmonella enterica Typhimurium on grape tomato (Lycopersicon esculentum). Grape tomatoes were dip‐inoculated with inoculum of S. enterica Typhimurium TISTR 292 (ATCC 13311) (9.79 ± 0.39 log CFU mL−1) and allowed to dry before treatments. The pre‐inoculated samples were exposed to 0.15–0.85 mg of ClO2 gas, for up to 58 min. The treatments at 4 and 25 °C resulted in population reductions of S. enterica Typhimurium of up to 3.95 ± 0.22 and 7.37 ± 0.39 log CFU per fruit, respectively. The population reduction results were used to construct statistical models to predict efficacy of ClO2 gas. The second‐order equations for treatments at 4 and 25 °C had R2 of 0.87 and 0.95, respectively, and indicated that efficacy of ClO2 gas was significantly influenced by ClO2 gas level, exposure time and treatment temperature.

Evaluation of chlorine dioxide as an antimicrobial against Botrytis cinerea in California strawberries

Abstract Strawberries are highly sensitive to deterioration by microbial decay after harvest and Botrytis cinerea is one of the most common diseases that infect them. Previous work has reported successful extension of strawberry shelf life through the use of chlorine dioxide (ClO2) gas treatments. In this study, California strawberries purchased at retail stores were treated with continuously generated ClO2 gas over concentrations ranging from 0.01 to 5.0 mg/L for durations ranging from 7 to 1000 min to determine how ClO2 gas impacts fungal mortality and fruit quality as a function of treatment concentration, treatment duration, and ClO2 absorption by the fruit. Repeated measures and Gompertz models were used to infer on the efficacy of the ClO2 gas, and a novel method was used to quantify the ClO2 absorption by fresh produce. It was found that ClO2 gas treatments have minimal effect at delaying the onset or growth rate of Botrytis cinerea for treatments followed by incubation at 4 or 22 °C even when corrected for natural variability of Botrytis cinerea presence among batches of strawberries, indicating that treatments are not sufficient for shelf-life extension.

Kinetics of Inactivation of Bacillus subtilis subsp. niger Spores and Staphylococcus albus on Paper by Chlorine Dioxide Gas in an Enclosed Space.

Bacillus subtilis subsp. niger spore and Staphylococcus albus are typical biological indicators for the inactivation of airborne pathogens. The present study characterized and compared the behaviors of B. subtilis subsp. niger spores and S. albus in regard to inactivation by chlorine dioxide (ClO2) gas under different gas concentrations and relative humidity (RH) conditions. The inactivation kinetics under different ClO2 gas concentrations (1 to 5 mg/liter) were determined by first-order and Weibull models. A new model (the Weibull-H model) was established to reveal the inactivation tendency and kinetics for ClO2 gas under different RH conditions (30 to 90%). The results showed that both the gas concentration and RH were significantly (P < 0.05) and positively correlated with the inactivation of the two chosen indicators. There was a rapid improvement in the inactivation efficiency under high RH (>70%). Compared with the first-order model, the Weibull and Weibull-H models demonstrated a better fit for the experimental data, indicating nonlinear inactivation behaviors of the vegetative bacteria and spores following exposure to ClO2 gas. The times to achieve a six-log reduction of B. subtilis subsp. niger spore and S. albus were calculated based on the established models. Clarifying the kinetics of inactivation of B. subtilis subsp. niger spores and S. albus by ClO2 gas will allow the development of ClO2 gas treatments that provide an effective disinfection method. Chlorine dioxide (ClO2) gas is a novel and effective fumigation agent with strong oxidization ability and a broad biocidal spectrum. The antimicrobial efficacy of ClO2 gas has been evaluated in many previous studies. However, there are presently no published models that can be used to describe the kinetics of inactivation of airborne pathogens by ClO2 gas under different gas concentrations and RH conditions. The first-order and Weibull (Weibull-H) models established in this study can characterize and compare the behaviors of Bacillus subtilis subsp. niger spores and Staphylococcus albus in regard to inactivation by ClO2 gas, determine the kinetics of inactivation of two chosen strains under different conditions of gas concentration and RH, and provide the calculated time to achieve a six-log reduction. These results will be useful to determine effective conditions for ClO2 gas to inactivate airborne pathogens in contaminated air and other environments and thus prevent outbreaks of airborne illness.

Response surface modeling for the inactivation of Bacillus subtilis subsp. niger spores by chlorine dioxide gas in an enclosed space

ABSTRACTBacillus subtilis subsp. niger spores are a commonly used biological indicator to evaluate the disinfection of an enclosed space. In the present study, chlorine dioxide (ClO2) gas was applied to inactivate B. subtilis subsp. niger spores in an enclosed space. The effects of the ClO2 gas concentration (1-3 mg/l), relative humidity (RH, 30-70%) and exposure time (30-90 min) were investigated using a response surface methodology (RSM). A three-factor Box-Behnken experimental design was used. The obtained data were adequately fitted to a second-order polynomial model with an R2adj of 0.992. The ClO2 gas concentration, RH and exposure time all significantly (P<0.05) and positively correlated with the inactivation of B. subtilis subsp. niger spores. The interaction between the ClO2 gas concentration and RH as well as that between the exposure time and RH indicated significant and synergistic effects (P<0.05). The predictive model was validated by additional eight experiments and proven to be with good accuracy. Overall, this model established by the RSM could show the trend of the inactivation of spores, indicate the interactions between important factors, and provide a reference to determine effective conditions for the disinfection in different enclosed spaces by ClO2 gas.Implications: The inactivation of indoor biological contaminants plays an important role in preventing the transmission of pathogens and ensuring human safety. The predictive model using response surface methodology indicates the influence and interaction of the main factors on the inactivation of Bacillus subtilis subsp. niger spores by ClO2 gas, and can predict a ClO2 gas treatment condition to achieve an effective sterilization of enclosed spaces. The results in this paper will provide a reference for the application of ClO2 gas treatments for indoor disinfection.

Insecticidal activity of chlorine dioxide gas by inducing an oxidative stress to the red flour beetle, Tribolium castaneum

Chlorine dioxide (ClO2) is a commercial bleaching and disinfection agent. Its fumigant formulation at 200 ppm for 24 h exposure gave a complete lethality to both larvae and adults of the red flour beetle, Tribolium castaneum. This study set up a hypothesis that oxidative stress induced by ClO2 treatment is a main factor to kill the beetles. To test this hypothesis, two antioxidant enzymes (superoxide dismutase (SOD) and thioredoxin-peroxidase (Tpx)) were annotated from the insect genome and analyzed in their functional links to oxidative stress. An oxidative stress to T. castaneum was simulated by an immune challenge. Gene expressions of both SOD and Tpx were upregulated in the larvae challenged by bacteria. Similarly, an exposure to ClO2 gas significantly induced the larvae to up-regulate the gene expressions of both SOD and Tpx. Either RNA interference of SOD or Tpx using specific double-stranded RNAs significantly enhanced the lethal activity of the ClO2 gas treatment. Reactive oxygen species (ROS) amounts were significantly enhanced by the bacterial challenge or ClO2 treatment. These results suggest that ClO2 gas induces an oxidative stress by generating ROS, which can be detoxified by the antioxidant activities of SOD and Tpx of T. castaneum. Thus, the excessive oxidative stress derived from a lethal concentration of ClO2 is an insecticidal factor against T. castaneum.

Oxidative stress induced by chlorine dioxide as an insecticidal factor to the Indian meal moth, Plodia interpunctella

A novel fumigant, chlorine dioxide (ClO2) is a commercial bleaching and disinfection agent. Recent study indicates its insecticidal activity. However, its mode of action to kill insects is yet to be understood. This study set up a hypothesis that an oxidative stress induced by ClO2 is a main factor to kill insects. The Indian meal moth, Plodia interpunctella, is a lepidopteran insect pest infesting various stored grains. Larvae of P. interpunctella were highly susceptible to ClO2 gas, which exhibited an acute toxicity. Physiological damages by ClO2 were observed in hemocytes. At high doses, the larvae of P. interpunctella suffered significant reduction of total hemocytes. At low doses, ClO2 impaired hemocyte behaviors. The cytotoxicity of ClO2 was further analyzed using two insect cell lines, where Sf9 cells were more susceptible to ClO2 than High Five cells. The cells treated with ClO2 produced reactive oxygen species (ROS). The produced ROS amounts increased with an increase of the treated ClO2 amount. However, the addition of an antioxidant, vitamin E, significantly attenuated the cytotoxicity of ClO2 in a dose-dependent manner. To support the oxidative stress induced by ClO2, two antioxidant genes (superoxide dismutase (SOD) and thioredoxin-peroxidase (Tpx)) were identified from P. interpunctella EST library using ortholog sequences of Bombyx mori. Both SOD and Tpx were expressed in larvae of P. interpunctella especially under oxidative stress induced by bacterial challenge. Exposure to ClO2 gas significantly induced the gene expression of both SOD and Tpx. RNA interference of SOD or Tpx using specific double stranded RNAs significantly enhanced the lethality of P. interpunctella to ClO2 gas treatment as well as to the bacterial challenge. These results suggest that ClO2 induces the production of insecticidal ROS, which results in a fatal oxidative stress in P. interpunctella.

Antimicrobial effect of chlorine dioxide gas against foodborne pathogens under differing conditions of relative humidity

The objective of this study was to determine the influence of relative humidity (RH) on the antimicrobial effect of chlorine dioxide (ClO2) gas against Escherichia coli O157:H7, Salmonella Typhimurium, and Listeria monocytogenes on spinach leaves. Spinach leaves were inoculated with three foodborne pathogens and treated with ClO2 gas at different concentrations (1, 5, 10, 30, and 50 ppmv) for 0, 5, 10, 15, and 20 min under differing conditions of RH (50, 70, and 90%). Inoculated spinach leaves subjected to ClO2 gas treatments experienced significant reductions, with pathogen populations reduced more under conditions of 90% than under 50 and 70% RH. Generally, there were no significant differences (p > 0.05) in reduction levels of the three foodborne pathogens between 50 and 70% RH. Exposure to 50 ppmv of ClO2 gas for 20 min resulted in 1.25–1.78 (50% RH) and 2.02 to 2.54 (70% RH) log reductions of the three foodborne pathogens. The levels of the three foodborne pathogens was reduced to below the detection limit (1 log CFU/g) within 15 min when treated with 50 ppmv of ClO2 gas under 90% RH. The results may help the fresh produce industry to establish effective conditions for ClO2 gas treatment.