ClO2 Treatment Research Articles

Evaluation of chlorine dioxide as a supplementary pretreatment reagent for lignocellulosic biomass

Chlorine dioxide (ClO2) is a bleaching reagent used in paper industry. Two different types of pretreatment methods were investigated incorporating ClO2 as a secondary reagent: (a) alkaline followed by ClO2 treatment; (b) dilute-sulfuric acid followed ClO2 treatment. In these methods, ClO2 treatment has shown little effect on delignification. Scheme-a has shown a significant improvement in enzymatic digestibility of glucan far above that treated by ammonia alone. On the contrary, dilute-acid followed by ClO2 treatment has shown negative effect on the enzymatic hydrolysis. The main factors affecting the enzymatic hydrolysis are the changes of the chemical structure of lignin and its distribution on the biomass surface. ClO2 treatment significantly increases the carboxylic acid content and reduces phenolic groups of lignin, affecting hydrophobicity of lignin and the H-bond induced association between the enzyme and lignin. This collectively led to reduction of unproductive binding of enzyme with lignin, consequently increasing the digestibility.

Aqueous chlorine dioxide treatment of horticultural produce: Effects on microbial safety and produce quality–A review

ABSTRACTMicrobial load on fresh fruit and vegetables causes decay and losses after harvest and may lead to foodborne illness in case of contamination with human pathogens on raw consumed produces. Washing with tap water only marginally reduces microorganisms attached to produce surfaces. Chlorine is widely used for decontamination on fresh horticultural produces. However, due to harmful by-products and the questionable efficacy it has become increasingly challenged. During the last 20 years, the interest to study ClO2 treatments as an alternative sanitation agent for industrially prepared fresh produce has largely increased. For a wide range of commodities, the application of gaseous ClO2 has meanwhile been investigated. In addition, since several years, the interest in aqueous ClO2 treatments has further risen because of the better manageability in postharvest processing lines compared to gaseous application. This article critically evaluated the effects of postharvest application of aqueous ClO2, either alone or in combination with other treatments, on microbial loads for various horticultural produces. In laboratory investigations, application of aqueous ClO2 at concentrations between 3 and 100 ppm effectively reduced counts of natural or inoculated microorganisms (bacteria, yeasts, and mold) in the range of 1 and 5 log. However, various effects of ClO2 treatments on produce quality have been described. These mainly comprise implication on sensory and visual attributes. In this context, there is increasing focus on the potential impacts of aqueous ClO2 on relevant nutritional components of produces such as organic acids or phenolic substances.

Effects of chlorine dioxide fumigation on redox balancing potential of antioxidative ascorbate-glutathione cycle in ‘Daw’ longan fruit during storage

Redox status in ascorbate-glutathione (ASA-GSH) cycle plays a pivotal role in plant responses to physiological and environmental changes. The change of ASA-GSH redox potential is associate with oxidative stress leading to plant senescence. The present study was aimed to investigate the effects of gaseous ClO2 on the redox status involved in delaying fruit senescence during storage of harvested longan fruit (Dimocarpus longan Lour. cv. Daw). Fresh longan fruit were fumigated with 10mg/L ClO2 for 10min, packed into cardboard boxes and stored at room temperature for 7 d. The results show that redox status of the fruit determined by ASA/DHA, GSH/GSSG and NADPH/NADP ratios decreased steadily in ClO2 untreated control group during storage. On the contrary, those ratios increased immediately after ClO2 treatment before declining steadily afterwards. The activities of NADPH-generating dehydrogenases including glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase, and ASA-GSH cycle enzymes including ascorbate peroxidase, monodehydroascorbate reductase, dehydroascorbate reductase and glutathione reductase were upregulated upon the ClO2 treatment and remained stable for a few days. ClO2 treatment decreased hydrogen peroxide content and fruit senescence index, including browning and disease symptoms in pericarp during storage. It was concluded that the imbalance of redox status of ASA-GSH cascade involved senescence in ‘Daw’ longan, and ClO2 could maintain the redox balance, leading to the alleviation and delay fruit senescence.

CHLORINE DIOXIDE GAS TREATMENT ON POSTHARVEST QUALITY OF RASPBERRY

The study investigated the effects of chlorine dioxide (ClO2) gas on the postharvest quality of raspberries (cv Grandeur) during storage. Weight loss, color, total soluble solids content (TSSC), titratable acidity (TA), pH, vitamin C, total phenols, anthocyanins and antioxidant capacity were evaluated. The ClO2 positively influenced weight loss, color, TA, TSSC and antioxidant capacity. Moreover, ClO2 treatment decreased the total yeast and mold count. In contrast, the vitamin C, anthocyanins and total phenolics were not influenced by the ClO2 treatment.

Controlled-release of Chlorine Dioxide in a Perforated Packaging System to Extend the Storage Life and Improve the Safety of Grape Tomatoes.

A controlled-release chlorine dioxide (ClO2) pouch was developed by sealing a slurry form of ClO2 into semipermeable polymer film; the release properties of the pouch were monitored in containers with or without fruit. The pouch was affixed to the inside of a perforated clamshell containing grape tomatoes, and the effect on microbial population, firmness, and weight loss was evaluated during a 14 day storage period at 20 °C. Within 3 days, the ClO2 concentration in the clamshells reached 3.5 ppm and remained constant until day 10. Thereafter, it decreased to 2 ppm by day 14. The ClO2 pouch exhibited strong antimicrobial activity, reducing Escherichia coli populations by 3.08 log CFU/g and Alternaria alternata populations by 2.85 log CFU/g after 14 days of storage. The ClO2 treatment also reduced softening and weight loss and extended the overall shelf life of the tomatoes. Our results suggest that ClO2 treatment is useful for extending the shelf life and improving the microbial safety of tomatoes during storage without impairing their quality.

Survival of Salmonella Typhimurium on soybean sprouts following treatments with gaseous chlorine dioxide and biocontrol Pseudomonas bacteria.

Control of Salmonella Typhimurium on sprouts is crucial for food and consumer safety. In this study, natural microflora on soybean seed was assessed and effects of gaseous chlorine dioxide (ClO2) and biocontrol Pseudomonas on the survival of S. Typhimurium on soybean sprouts were evaluated. Sprouts were dip-inoculated with S. Typhimurium prior to the application of the biocontrol (P. chlororaphis and P. fluorescens). After inoculation with S. Typhimurium, the sprouts were treated with ClO2 at 0.4 mg/L for 1 h (90% R.H., 13°C). Pseudomonas strains and Salmonella were recovered on Pseudomonas Agar F (PAF) and xylose lysine tergitol-4 (XLT-4) media, respectively. Pseudomonas strains reduced Salmonella by <1 log colony forming units (CFU)/g of sprouts, whereas S. Typhimurium on soybean sprouts was reduced from 2.55 to 5.35 logs CFU/g by ClO2. Gaseous ClO2 treatment reduced S. Typhimurium by 3.90 (0 h), 4.47 (24 h), and 3.61 log CFU/g (168 h). It was concluded that ClO2 and biocontrol treatment can enhance sprout safety.

Chlorine dioxide as an alternative antifouling biocide for cooling water systems: Toxicity to larval barnacle Amphibalanus reticulatus (Utinomi)

Chlorine dioxide (ClO2) is seen as an effective alternative to chlorine, which is widely used as an antifouling biocide. However, data on its efficacy against marine macrofoulants is scanty. In this study, acute toxicity of ClO2 to larval forms of the fouling barnacle Amphibalanus reticulatus was investigated. ClO2 treatment at 0.1mg/L for 20min elicited 45–63% reduction in naupliar metamorphosis, 70% inhibition of cyprid settlement and 80% inhibition of metamorphosis to juveniles. Increase in concentration to 0.2mg/L did not result in any significant difference in the settlement inhibition or metamorphosis. Treatment with 0.2mg/L of ClO2 elicited substantial reduction in the settlement of barnacle larvae compared to control. The study indicates the possibility of using ClO2 as an alternative antifouling biocide in power plant cooling water systems. However, more work needs to be done on the environmental effects of such switchover, which we are currently undertaking.

Influence of temperature and organic matter load on chlorine dioxide efficacy on Escherichia coli inactivation

Postharvest losses of fresh vegetables are mostly caused by microbial infections. Furthermore, contamination of raw-consumed fruits and vegetables with human pathogens may lead to serious foodborne illness. Washing with tap water reduces the total number of produce surface attached microorganisms by only 1–2 log. Addition of sanitizers to washing waters can help to effectively reduce the microbial load. However, some sanitizers are less successful than initially assumed and/or may negatively affect produce quality. During recent years, efficiency of chlorine dioxide (ClO2) applications was tested as an alternative sanitation agent for fresh produce. Most published studies, however, were planned and performed under laboratory conditions, i.e. in tap water with a low chemical oxygen demand (COD). Thus, they do not necessarily reflect the practical conditions in processing lines, where effluent produce sap may largely increase COD. Factors such as pH, temperature and load of organic matter may influence the actual biocidal efficiency of ClO2. Successful technical implementations, thus, require information about the relationship between efficiency of ClO2 and influencing factors. Here, a comprehensive evaluation of the influence of temperature on the effectiveness of ClO2 treatment (ClO2 concentrations = 0, 2, 4, 6, 8 and 10 mg L−1) on Escherichia coli (starting load: 5 105 cfu mL−1) and the influence of organic matter load on the effective ClO2 concentration in lettuce washing water is provided. Decreasing the temperature of the processing water (from 15 °C to 2 °C) resulted in a reduced and delayed reduction of E. coli counts. At 15 °C, not at 2 °C, a significant reduction of E. coli was found after 2 min. At a ClO2 concentration of 3 mg L−1, microbes were significantly and completely inactivated at 15 °C after 0.5 min. In contrast, E. coli loads were significantly, but only incompletely reduced at 2 °C after 1 min. The increase in COD from 250 mg L−1 to 1000 mg L−1 by the addition of respective amounts of organic matter resulted in a pronounced increase in the ClO2 demand.

Correlation of Conformational Changes and Protein Degradation with Loss of Lysozyme Activity Due to Chlorine Dioxide Treatment.

Chlorine dioxide (ClO2) is a potent oxidizing agent used for the treatment of drinking water and decontamination of facilities and equipment. The purpose of this research is to elucidate the manner in which ClO2 destroys proteins by studying the effects of ClO2 on lysozyme. The degree of enzyme activity lost can be correlated to the treatment time and levels of the ClO2 used. Lysozyme activity was drastically reduced to 45.3% of original enzyme activity when exposed to 4.3mM ClO2 in the sample after 3h. Almost all activities were lost in 3h after exposure to higher ClO2 concentrations of up to 16.8 and 21.9mM. Changes in protein conformation and amount as a result of ClO2 treatment were determined using the Raman spectroscopy and gel electrophoresis. Raman shifts and the alteration of spectral features observed in the ClO2-treated lysozyme samples are associated with loss of the α-helix secondary structure, tertiary structure, and disulfide bond. Progressive degradation of the denatured lysozyme by increasing levels of chlorine dioxide was also observed in gel electrophoresis. Hence, ClO2 can effectively cause protein denaturation and degradation resulting in loss of enzyme activity.

Decontamination of alfalfa and mung bean sprouts by ultrasound and aqueous chlorine dioxide

The antimicrobial effect of ultrasound, aqueous chlorine dioxide (ClO2) and the combination of both treatments was assessed on Escherchia coli and Salmonella enteritidis inoculated on alfalfa and mung bean sprouts were performed for 5 min. This work presents the first approach regarding the using of the previously mentioned technologies on the decontamination of inoculated sprouts. Ultrasound (26 kHz, 90 μm, 200 W) process was able to reduce by 1.40 ± 0.40 and 1.89 ± 0.51 log CFU/g Salmonella and by 1.06 ± 0.32 and 1.23 ± 0.40 log CFU/g of E. coli on alfalfa and mung bean sprouts, respectively. ClO2 (3 ppm) reduced the population of the studied bacteria in similar levels (≈1.5 log CFU/g) both in alfalfa and mung bean sprouts. However, ClO2 treatment was more effective than the ultrasound process in terms of E. coli and Salmonella total inactivation (i.e., water and sprouts) both in alfalfa and mung bean sprouts. Additionally, an additive effect was observed in the reduction of both E. coli and Salmonella and the total inactivation when ultrasound was combined with ClO2 in all tested food products.

Inactivation of Salmonella Typhimurium and quality preservation of cherry tomatoes by in-package aerosolization of antimicrobials

The purpose of the present study was to investigate the efficacy of in-package aerosolized aqueous sanitizers in reducing populations of Salmonella enterica serovar Typhimurium on tomato fruit and in maintaining fruit quality. Cherry tomatoes were inoculated with a cocktail of attenuated S. Typhimurium ATCC 53647 and 53648 strains on the smooth skin surface and stem scar area. Next, 200 ppm free chlorine, and peroxyacetic acid (PAA) and aqueous ClO2 at different concentrations, 2% lactic acid + 2% acetic acid + 2% levulinic acid, and 3% acetic acid + 3% lactic acid were aerosolized into a clamshell container containing cherry tomatoes. Results showed that S. Typhimurium populations on smooth tomato surfaces were reduced by more than 5 log CFU/fruit with 400 ppm PAA, 2% lactic acid + 2% acetic acid + 2% levulinic acid, 3% acetic acid + 3% lactic acid, and aqueous ClO2 (100 and 400 ppm). On the stem scar area, 400 ppm aqueous ClO2 was more effective in reducing S. Typhimurium populations than other treatments, achieving 4.89 log CFU/fruit reduction, followed by 400 ppm PAA (2.62 log CFU/fruit). The efficacy of ClO2 and acid combination treatments increased during 3-week storage at 10 °C, achieving >3 log CFU/fruit inactivation with the acid combination and ca. 6 log with for 400 ppm with ClO2. None of the treatments significantly (p > 0.05) affected color, appearance, firmness, vitamin C, lycopene or antioxidant values of tomatoes during 3 weeks of storage; although, an acidic odor was detected for samples treated with the organic acids in the earlier period of the storage. These results suggest that in-package aerosolized sanitizers can be used as a novel method for the inactivation of Salmonella on tomato fruit.

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.

Cultural, Chemical, and Alternative Control Strategies for Rhizopus Soft Rot of Sweetpotato.

Rhizopus soft rot, caused primarily by Rhizopus stolonifer, is one of the most common postharvest diseases of sweetpotato and is often considered the most devastating. Traditionally, Rhizopus soft rot has been effectively controlled using postharvest dips in dicloran fungicides; however, due to changes in market preferences, use of these fungicides is now limited. This, along with the lack of labeled and effective fungicides for control of Rhizopus soft rot in sweetpotato, creates the need for integrated strategies to control the disease. The effects of storage temperature (13, 23, and 29°C), relative humidity (80, 90, and 100%), and initial inoculum levels (3-, 5-, and 7-mm-diameter mycelial plugs) on progression of Rhizopus soft rot in 'Covington' sweetpotato were examined. Percent decay due to Rhizopus soft rot infection was significantly reduced (P < 0.0001) at a low temperature (13°C) but was not significantly affected by changes in relative humidity or initial inoculum level (P >0.05). Sporulation of R. stolonifer was also significantly reduced at the lowest temperature of 13°C. High relative humidity (>95%) significantly increased sporulation of R. stolonifer and sporulation also increased as initial inoculum level increased. Efficacy of chlorine dioxide (ClO2) fumigation, UV-C irradiation, and postharvest dips in alternative control products were also investigated for control of Rhizopus soft rot. Static ClO2 treatments were effective in reducing sporulation on treated roots but had no significant impact on incidence of Rhizopus soft rot. UV irradiation at 3.24 KJ/m2 1 h after inoculation as well as dips in aqueous ClO2 and StorOx 2.0 significantly (P < 0.05) reduced disease incidence. Understanding the epidemiological factors favoring Rhizopus soft rot and identifying alternative control strategies allow for improved recommendations to limit postharvest losses in sweetpotato.

Efficacy of chlorine dioxide disinfection to non-fermentative Gram-negative bacilli and non-tuberculous mycobacteria in a hospital water system

Chlorinated tap water in hospitals often contains low levels of non-fermentative Gram-negative bacilli (NFGNB) and non-tuberculous mycobacteria (NTM). Measures are needed to ensure a safe water supply in hospitals to prevent nosocomial infections from these waterborne pathogens. To evaluate the efficacy of ClO2 treatment of a hospital water system on the levels of NFGNB and NTM in the water. Our institution is a 1000-bed medical centre with two main buildings (B1 and B2). B1 has three intensive care units (ICUs) and transplant wards and polyethylene water pipes. B2 (control) has no ICUs and galvanized water pipes. A ClO2 generating unit was installed in the water system of B1 in April 2012 and water samples were collected in B1 and B2 before and eight times after installation. All samples were cultured for NFGNB and NTM. The ClO2 concentration was significantly lower in the hot water than in the cold water (P<0.001). After 40 weeks of ClO2 use, the overall NFGNB colonies decreased significantly (hot water: 160±143 vs 2±4cfu/mL, P<0.001; cold water: 108±138 vs 3±7cfu/mL, P<0.001). Highly prevalent nosocomial NFGNB, such as Pseudomonas spp. and Stenotrophomonas spp., were undetected three months after ClO2 disinfection; Sphingomonas spp. persisted but had lower colony counts. NTM was present in 25% (three out of 12) of sampling locations initially, but was not detected at two weeks after ClO2 disinfection. The ICUs had no overall change in the number of NFGNB nosocomial infections after the intervention. Addition of a ClO2 disinfection unit to our hospital water system reduced the numbers of NTM and NFGNB in the hot and cold water systems.

Effect of Chlorine Dioxide on Freshness of ‘Maehyang’ Strawberries during Export

The objective of this study was to assess the effect of precooling and application of gaseous ClO2 on the retention of freshness and quality of ‘Maehyang’ strawberry fruits intended for export. ‘Maehyang’ strawberry fruits (Fragaria × ananassa Duch.) were grown in commercia greenhouses and then harvested. Fruits of uniform and medium size at 60% ripeness were selected and assigned to one of four treatment groups: non-treatment (control), precooling only (PO), gaseous ClO2 only (GCO) or precooling combined with gaseous ClO2 (P + C). Weight loss was lowest in the PO treatment and greatest in the GCO treatment after export. Compared to the control and PO treatment groups, strawberry fruits in the GCO treatment group maintained high brightness and high chroma. Six days after shipping, fruits in the P + C treatment group had the highest soluble solids content, even as high as 10.05 °Brix; the lowest value was observed in the PO treatment. The incidence rate of gray mold in strawberry fruits was 20% and 17% in the control and the PO treatment, respectively; in the GCO treatment, the incidence rate of gray mold amounted to 10%. No gray mold was observed in the P + C treatment group. These results indicate that gaseous ClO2 treatment combined with precooling (P + C) was effective in maintaining the freshness of ‘Maehyang’ strawberry fruits intended for export from South Korea to Hong Kong.

Viability of sprout seeds as affected by treatment with aqueous chlorine dioxide and dry heat, and reduction of Escherichia coli O157:H7 and Salmonella enterica on pak choi seeds by sequential treatment with chlorine dioxide, drying, and dry heat

Germination rates of 11 types of sprout seeds (alfalfa, broccoli, kohlrabi, kyona, mustard, pak choi, red kohlrabi, red radish, red young radish, tatsoi, and violet radish) treated with ClO2 (200 μg/ml, 5 min) or dry-heat (80 °C/23% relative humidity [RH], 24 h) were determined. Pak choi, red radish, and tatsoi seeds showed highest tolerance to both ClO2 and dry-heat treatments. Next, pak choi seeds were inoculated with Escherichia coli O157:H7 (5.4 log CFU/g) or Salmonella enterica (4.8 log CFU/g) and sequentially treated with ClO2 (200 μg/ml, 5 min), drying (45 °C/23% RH, 24 h), and dry heat (80 °C/23% RH, 48 h). E. coli O157:H7 was inactivated, but S. enterica was not eliminated (>3.8 log CFU/g reduction). Pak choi seeds inoculated with the pathogens were treated with ClO2, drying, and dry heat and subsequently sprouted for 5 days. When seeds were not completely decontaminated, initial populations of E. coli O157:H7 and S. enterica on seeds (<1.0 log CFU/g) increased to >5.3 and > 8.4 log CFU/g of sprouts, respectively. This study shows that sequential treatments of pak choi seeds with ClO2, drying, and dry heat are effective in reducing large numbers of E. coli O157:H7 and S. enterica without loss of seed viability.

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.

DEVELOPMENT OF A PRESERVATION TECHNIQUE FOR STRAWBERRY FRUIT (FRAGARIA × ANANASSA DUCH.) BY USING AQUEOUS CHLORINE DIOXIDE

Effects of aqueous chlorine dioxide (ClO2) treatment on preserving strawberry fruit (Fragaria × ananassa Duch.) were investigated. A stabilized ClO2 powder was dissolved in water to prepare the ClO2 solution. Strawberry fruit were then rinsed with ClO2 solutions at different concentrations (20, 40, 60, and 80 mg/L) for different times (5, 10, and 15 min) at 22±2℃ and 70±5% RH. Following ClO2 treatments, strawberries were stored at 4℃ for 9 days. ClO2 could markedly delay changes in firmness, slow down weight loss, and decay, and maintain sensory quality of strawberry fruit. ClO2 was also effective in retention of ascorbic acid, reducing sugar, and titratable acid. ClO2 concentration and treatment time were two significant factors (P

The efficacy of the combined use of chlorine dioxide and passive modified atmosphere packaging on sweet cherry quality

The efficacy of the combined use of passive modified atmosphere and aqueous chlorine dioxide at various concentrations of 4, 8, 12, 16, 20 and 25mg/L on physical and chemical quality attributes of sweet cherry was evaluated during a five weeks storage period at 4°C. The results showed that ClO2 treatments at concentrations of 16 and 20mg/L maintained pH, total soluble solid contents and firmness better than other samples at the end of the storage. Untreated samples and samples treated with 25mg/L ClO2, had higher weight loss and respiration rate than other treated fruit during storage. Steady-state equilibrium was achieved in the passive modified atmosphere packages of ClO2 treated cherries between the second and the fifth weeks of storage. No significant differences were found between untreated and treated samples except for 25mg ClO2 treated fruit regarding electrolyte leakage. The L* values of ClO2 treated samples ascended with increasing concentrations of ClO2 at each sampling day. ClO2 treatments significantly affected the redness (a*) values of fruit during storage. ClO2 treatment at the concentration of 25mg/L had a deleterious effect on cherry color and anthocyanins. The cherries treated with 16 and 20mg/L ClO2 tended to have higher scores than other treated and untreated samples in all sensory attributes. No mold growth was visually observed during the first two weeks of storage in treated cherries except 4 and 8mg/L ClO2 treated samples. In summary, our work has led us to conclude that combined use of passive modified atmosphere and ClO2 treatments at a concentrations of 16 and 20mg/L has potential to maintain the quality of sweet cherry.

Reduction of Salmonella enterica on the surface of eggshells by sequential treatment with aqueous chlorine dioxide and drying

The synergistic effects of sequential treatments with chlorine dioxide (ClO2) and drying in killing Salmonella enterica on the surface of chicken eggshells were investigated. Initial experiments were focused on comparing lethalities of sodium hypochlorite (NaOCl) and ClO2. Eggs surface-inoculated with S. enterica in chicken feces as a carrier were immersed in water, NaOCl (50 or 200μg/mL), or ClO2 (50 or 200μg/mL) for 1 or 5min. For 1-min treatments, lethal activities of sanitizers were not significantly different (P>0.05). However, after treatment with ClO2 for 5min, reductions of S. enterica were significantly greater (P≤0.05) than reductions after treatment with water or NaOCl. The effect of treatment of eggs with ClO2 or NaOCl, followed by drying at 43% relative humidity and 25°C for 24 and 48h, were determined. Populations of S. enterica decreased during drying, regardless of the type of sanitizer treatment. ClO2 treatment, compared to water or NaOCl treatments, resulted in additional reductions of ca. >1.3logCFU/egg during drying. This indicates that sequential treatments with ClO2 and drying induced synergistic lethal effects against S. enterica on the surface of eggshells. These observations will be useful when selecting a sanitizer to control S. enterica on the surface of eggshells and designing an effective egg sanitization system exploiting the synergistic lethal effects of sanitizer and drying.