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

Maintenance of cell integrity during hydroxyl radical rapid inactivation of Pseudanabaena sp. and simultaneous mineralization of odor compound 2-methylisoborneol

Pseudanabaena sp. and the odor compound it produces, 2-methylisoborneol (2-MIB), has been reportedly responsible for off-flavor pollution worldwide, leading to substandard drinking water sensory indicators and serious water supply crises. In this paper, the hydroxyl radical (•OH) produced by the synergistic effect of strong ionization discharge and hydrodynamic cavitation rapidly inactivated Pseudanabaena sp. and simultaneously mineralized 2-MIB to a concentration of 2.57 ng/L, which is below the odor threshold of 10 ng/L for a total reactive oxidants (TRO) concentration of 1.2 mg/L within 12 s. Crucially, the intracellular 2-MIB level was maintained in approximately 155.26- 162.29 ng/L range, indicating that 2-MIB was not released from the cells. Based on the scanning electron microscopy (SEM) results, the integrity of Pseudanabaena sp. cells was maintained with intact membranes and no intracellular organic matters (IOM) released during •OH inactivation. In contrast, ClO2 caused severe membrane rupture and massive IOM release. Based on the gas chromatograph/mass spectrometer (GC/MS) analyses and mass spectral database, the chromatogram fitted the baseline with a TRO concentration of 4 mg/L and no peaks corresponding to intermediates were detected. Moreover, •OH could mineralize 2-MIB by opening the ring structures of 1,2,3,3-tetramethyl-4-cyclopentenone, neomenthol, and 2-methylcyclohexene-1-aldehyde to produce small-molecule compounds, finally leading to CO2 and H2O formation via three reaction pathways. Therefore, the •OH not only maintained the cell integrity of Pseudanabaena sp. during inactivation but also mineralized 2-MIB simultaneously.

Self-triggered carboxymethyl chitosan hydrogel for the convenient sustained release of ClO2 gas with environmental stability and long-term antimicrobial effect

Challenges associated with the storage and uncontrolled release of ClO2 gas present significant hurdles to its practical application. Herein, a clever strategy for self-triggering the sustained release of chlorine dioxide (ClO2) gas is proposed by crosslinking carboxymethyl chitosan (CMCS) with Zn2+ to construct a novel CMCS-Zn@NaClO2 gel with eco-friendly, environmental stability, and convenient, long term, and efficient antibacterial activity. The precursor (NaClO2) in the CMCS solution was alkaline and triggered by the acidic Zn(NO3)2·6H2O solution to achieve sustained self-triggering ClO2 release. The ClO2 gas self-release could be sustained on demand at different temperatures for at least 20 days due to the environmental structure stability of the gel. The hydrogels showed an increase in pore size after sustained release. Molecular dynamics simulations showed the spontaneous release of ClO2 gas at room temperature and the contraction of the CMCS agglomeration, which were consistent with the macroscopic behaviour. The gel displayed a long-acting and high antibacterial efficacy, resulting in a bacteria-killing rate of over 99.9% (inhibitory concentrations of 2.5 mg mL-1 against E. coli and 0.16 mg mL-1 against S. aureus). The hydrogels could effectively extend the shelf life of fruits and demonstrated an excellent wide range of antibacterial properties. This work provides a new approach to solving the storage difficulty of ClO2 gas and offers a fresh perspective on the design of materials with convenient self-triggering release by a precursor, as well as the relationship between the material microstructure and sustained-release behaviour.

A pilot study comparing the disinfecting effects of commercialized stable ClO2 solution (free of activation) with conventional H2O2 on dental unit waterlines in the dental practice setting

Disinfection of dental unit waterlines (DUWLs) plays a key role in control and prevention of nosocomial infection in a dental clinic. The most conventional disinfectant is hydrogen peroxide (H2O2), while chlorine dioxide (ClO2) has been considered however was limited by the "activation" procedures. With the availability of commercialized stable ClO2 solution (free of activation), direct application of ClO2 in the dental practice became possible. This study was designed to compare the disinfecting effects of stable 5 ppm of ClO2 solution with conventional 0.24% of H2O2 on DUWLs in dental practice. Studies of colony-forming units (CFUs), confocal laser scanning microscopy (CLSM) and scanning electron microscope (SEM) were employed for evaluation. In CFUs studies, we found that the efficiency of ClO2 was no less than those of H2O2. In the morphological studies, the stronger disinfecting effects of ClO2 was verified by both CLSM and SEM studies for removal and prevention of biofilm. Importantly, ClO2 solution achieved a better disinfecting efficiency not only at the surface of bacterial biofilm, but also, it has penetrating effects, presented disinfecting effects from the surface to the bottom of the biofilm. This pilot study provided evidence regarding the efficiency of stable ClO2 solution on disinfection of DUWLs in the dental practice setting. Application of stable ClO2 solution in dental practice is therefore become possible.

Innovative nonthermal technologies for inactivation of emerging foodborne viruses

Various foodborne viruses have been associated with human health during the last decade, causing gastroenteritis and a huge economic burden worldwide. Furthermore, the emergence of new variants of infectious viruses is growing continuously. Inactivation of foodborne viruses in the food industry is a formidable task because although viruses cannot grow in foods, they can survive in the food matrix during food processing and storage environments. Conventional inactivation methods pose various drawbacks, necessitating more effective and environmentally friendly techniques for controlling foodborne viruses during food production and processing. Various inactivation approaches for controlling foodborne viruses have been attempted in the food industry. However, some traditionally used techniques, such as disinfectant-based or heat treatment, are not always efficient. Nonthermal techniques are considered a new platform for effective and safe treatment to inactivate foodborne viruses. This review focuses on foodborne viruses commonly associated with human gastroenteritis, including newly emerged viruses, such as sapovirus and Aichi virus. It also investigates the use of chemical and nonthermal physical treatments as effective technologies to inactivate foodborne viruses.

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.

Preparation and evaluation of a novel chlorine dioxide preservative based on citric acid grafted carboxymethyl chitosan

Instrument-free chlorine dioxide (ClO₂) preservative for fruit and vegetable has gained great attention due to its convenience and safety. In this study, a series of carboxymethyl chitosan (CMC) with citric acid (CA) substituents were synthesized, characterized, and further used to prepare a novel ClO₂ slow-releasing preservative for longan. UV-Vis and FT-IR spectra revealed that CMC-CA#1-3 were successfully prepared. Further potentiometric titration showed that the mass ratios of CA grafted in CMC-CA#1-3 were 0.18:1, 0.42:1, and 0.42:1, respectively. The composition and concentration of ClO₂ slow-releasing preservative were optimized, and the best formulation was as follows: NaClO₂:CMC-CA#2:Na₂SO₄:starch = 3:2:1:1. The maximum ClO₂ release time of this preservative reached >240 h at 5-25 °C, and the maximum release rate always occurred at 12-36 h. Longan treated with 0.15-1.2 g ClO₂ preservative had significantly (p < 0.05) higher L* and a* values but lower respiration rate and total microbial colony counts than the CK group (0 g ClO₂ preservative). After 17 days of storage, longan treated with 0.3 g ClO₂ preservative had the highest L* value of 47.47 and lowest respiration rate of 34.42 mg·kg^-1·h^-1, showing the best pericarp color and pulp quality. This study provided a safe, effective, and simple solution for longan preservation.

Enzymatic browning and polyphenol oxidase control strategies

Significant amounts of fresh and fresh-cut fruits and vegetables are wasted every year due to enzymatic browning. Polyphenol oxidase (PPO) is the key enzyme involved in the enzymatic browning. In the past decades, various methods have been developed to inhibit browning of various fresh produce items. However, for most fresh horticultural produce, ideal measures accepted by industries and consumers are still scarce. This review provides up-to-date knowledge of browning control technologies, including physical methods, chemical methods such as natural inhibitors, molecular biotechnology, and nanotechnology. In addition, we propose some ideas to improve the efficacies of these strategies with fewer side effects. To better inhibit tissue browning, new research directions are also discussed, for example, regulation of PPO substrate techniques.

Evaluation of oral care using MA-T gel for high-risk patients: a pilot study

BACKGROUND

Oral care with gel is a common method for preventing aspiration in high-risk patients. An oral care gel is used to clean and moisturize the oral cavity. However, the effects of gel care on the oral bacteria remain unclear. In this pilot study, we described a matching transformation system (MA-T) for elderly high-risk patients. MA-T is an on-demand aqueous chlorine dioxide solution that provides excellent safety and has various antimicrobial activities, even in the presence of abundant organic compounds. This study investigated the effects of MA-T gel in patients requiring nursing care.

MATERIALS AND METHODS

Patients who were hospitalized for nursing care were included in this study. No drugs and foods were administered orally. Oral bacteria and intraoral humidity were examined by daily care using MA-T gel. Moreover, oral membranous substances were analyzed and material from the oral cavity was cultured on selective media for identifying opportunistic organisms.

RESULTS

Membranous substances were present in the oral cavities of all patients. The number of bacteria decreased, and oral moisture improved, after treatment with MA-T gel. Moreover, oral humidity was also controlled with the continued use of MA-T gel. MA-T gels should be used not only for professional care but also on a daily basis for better oral care. Furthermore, the results of bacterial cultures showed that MA-T controls the propagation of opportunistic bacterial infections.

CONCLUSION

Membranous substances may be observed in the oral cavity of individuals requiring nursing care for tube feeding. The results of this pilot study suggest that MA-T, a novel disinfectant, can be used for oral care in the elderly to reduce the risk of aspiration-pneumonia.

Measurement of Water Vapor Condensation on Apple Surfaces during Controlled Atmosphere Storage

Apples are stored at temperatures close to 0 °C and high relative humidity (up to 95%) under controlled atmosphere conditions. Under these conditions, the cyclic operation of the refrigeration machine and the associated temperature fluctuations can lead to localized undershoots of the dew point on fruit surfaces. The primary question for the present study was to prove that such condensation processes can be measured under practical conditions during apple storage. Using the example of a measuring point in the upper apple layer of a large bin in the supply air area, this evidence was provided. Using two independent measuring methods, a wetness sensor attached to the apple surface and determination of climatic conditions near the fruit, the phases of condensation, namely active condensation and evaporation, were measured over three weeks as a function of the operating time of the cooling system components (refrigeration machine, fans, defrosting regime). The system for measurement and continuous data acquisition in the case of an airtight CA-storage room is presented and the influence of the operation of the cooling system components in relation to condensation phenomena was evaluated. Depending on the set point specifications for ventilation and defrost control, condensed water was present on the apple surface between 33.4% and 100% of the duration of the varying cooling/re-warming cycles.

Polyvinyl alcohol film with chlorine dioxide microcapsules can be used for blueberry preservation by slow-release of chlorine dioxide gas

Introduction

Chlorine dioxide (ClO₂) is a safe and efficient bactericide with unique advantages in reducing foodborne illnesses, inhibiting microbial growth, and maintaining the nutritional quality of food. However, gaseous ClO₂ is sensitive to heat, vibration, and light, which limits its application.

Methods

In this study, a ClO₂ precursor-stabilized ClO₂ aqueous solution was encapsulated by the double emulsion method, and a high-performance ClO₂ self-releasing polyvinyl alcohol (PVA) film was prepared to investigate its performance and effect on blueberry quality during storage.

Results

The self-releasing films had the best overall performance when the microcapsule content was 10% as the film's mechanical properties, thermal stability, and film barrier properties were significantly improved. The inhibition rates of Listeria monocytogenes and Escherichia coli were 93.69% and 95.55%, respectively, and the mycelial growth of Staphylococcus griseus was successfully inhibited. The resulting ClO₂ self-releasing films were used for blueberry preservation, and an experimental study found that the ClO₂ self-releasing antimicrobial film group delayed the quality decline of blueberries. During the 14-day storage period, no mold contamination was observed in the ClO₂ self-releasing film group, and blueberries in the antibacterial film group had higher anthocyanin accumulation during the storage period.

Discussion

Research analysis showed that films containing ClO₂ microcapsules are promising materials for future fruit and vegetable packaging.

Chlorine Dioxide Treatment Modulates Ripening-Related Genes and Antioxidant System to Improve the Storability of Tomato

Chlorine dioxide (ClO2) is used to maintain quality and safety of fresh produce. However, ClO2 action mechanism in fresh produce is unknown. In this study, firstly, we evaluated the efficacy of ClO2 treatment on the quality, chilling injury, and calyx molding of tomatoes stored at two different temperatures. Then, ClO2 effect on the expression of cell wall- and ripening-related genes and on the activity of antioxidant enzymes was investigated. Tomatoes were treated with gaseous ClO2 for 15 min before transferring them to 13°C for 12 days and/or 4°C for 14 days, followed by 5 days at 20°C (shelf-life conditions). ClO2 treatment marginally reduced the rate of respiration but did not affect ethylene production at 13°C and 4°C storage or at shelf-life conditions. When stored at 13°C, treatment with ClO2 reduced the loss of firmness, with concomitant repression of pectin esterase 1, a cell wall-related gene. Additionally, at 13°C storage conditions, ClO2 treatment maintained tomato quality in terms of soluble solid content, titratable acidity, and color and was associated with the downregulation of the ripening-relatedethylene response factors B3/C1/E1 and the induction of antioxidant genes encoding catalase and ascorbate peroxidase. At 4°C storage conditions, ClO2 at a concentration of 15 ppm not only maintained the firmness and quality of tomatoes but also inhibited pitting during shelf-life with a concomitant increase of catalase activity. Moreover, treatment with 15 ppm ClO2 significantly reduced the calyx molding that is generally observed in fruits stored at 13°C and under shelf-life conditions. Hence, our results indicate that ClO2 treatment effectively maintained tomato quality and inhibited calyx molding by partially regulating ripening-related genes and antioxidant systems, thereby improving the storability of postharvest tomatoes.

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

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

SARS-CoV-2 pseudotyped virus persists on the surface of multiple produce but can be inactivated with gaseous ozone

Due to the immense societal and economic impact that the COVID-19 pandemic has caused, limiting the spread of SARS-CoV-2 is one of the most important priorities at this time. The global interconnectedness of the food industry makes it one of the biggest concerns for SARS-CoV-2 outbreaks. Although fomites are currently considered a low-risk route of transmission for SARS-CoV-2, new variants of the virus can potentially alter the transmission dynamics. In this study, we compared the survival rate of pseudotyped SARS-CoV-2 on plastic with some commonly used food samples (i.e., apple, strawberry, grapes, tomato, cucumber, lettuce, parsley, Brazil nut, almond, cashew, and hazelnut). The porosity level and the chemical composition of different food products affect the virus's stability and infectivity. Our results showed that tomato, cucumber, and apple offer a higher survival rate for the pseudotyped viruses. Next, we explored the effectiveness of ozone in deactivating the SARS-CoV-2 pseudotyped virus on the surface of tomato, cucumber, and apple. We found that the virus was effectively inactivated after being exposed to 15 ppm of ozone for 1 h under ambient conditions. SEM imaging revealed that while ozone exposure altered the wax layer on the surface of produce, it did not seem to damage the cells and their biological structures. The results of our study indicate that ozonated air can likely provide a convenient method of effectively disinfecting bulk food shipments that may harbour the SARS-CoV-2 virus.

Safety evaluation of MA-T after ingestion in mice

MA-T (Matching Transformation System®) is a proprietary chemical mixture for on-demand production of aqueous chlorine dioxide that is used for the treatment of oral malodor. MA-T is also an effective disinfectant against at least 39 pathological microorganisms, including severe acute respiratory syndrome coronavirus 2, and therefore may be useful as a disinfectant mouthwash to prevent the spread of infection. Accidental ingestion is the putative worst hazard scenario associated with mouthwash use; therefore, here we investigated the safety of MA-T ingestion in mice. Mice were provided drinking water containing 0-3000 μg/ml MA-T for 7 days followed by non-spiked drinking water for an additional 14 days. At day 7, mice ingesting 1000 or 3000 μg/ml MA-T showed significantly decreased body weight and significantly increased liver, kidney, and heart tissue injury biomarkers compared with control. However, at 14 days after stopping MA-T ingestion, body weight and tissue injury biomarkers had returned to normal. Histological analysis revealed that MA-T-induced injuries in liver, kidney, spleen, stomach, duodenum, colon, and rectum had also recovered at 14 days after stopping MA-T ingestion; however, mild vascular endothelial injuries remained in heart, jejunum, and ileum in the worst-case scenario. Taken together, MA-T may be potentially safety for further development as a disinfectant mouthwash by risk management, such as placing a caution of the label and adding a distinctive flavor.

Fundamental Differences in Inactivation Mechanisms of Escherichia coli O157:H7 Between Chlorine Dioxide and Sodium Hypochlorite

Chlorine dioxide (ClO2) and sodium hypochlorite (NaClO) are two chlorinated oxidizing agents that are implemented in water treatment and postharvest processing of fresh produce. While the antibacterial mechanisms of NaClO have been investigated, there are comparatively few studies that have looked at how ClO2 kills bacteria. Therefore, the objective of this study was to compare the inactivation pathways of ClO2 and NaClO against Escherichia coli O157:H7. Treatments consisted of 2.5, 5, and 10 ppm ClO2 or 50, 100, and 200 ppm NaClO for 5, 10, and 15 min. Maximum log reductions of E. coli O157:H7 were 5.5 and 5.1 after treatment with ClO2 or NaClO, respectively. Bacterial inactivation was measured using log reductions, intracellular reactive oxygen species (ROS) using with 2′,7′–dichlorofluorescin diacetate (DCFDA) or aminophenyl fluorescein (APF) probes, relative values of NAD+, NADH, NADP+, and NADPH cofactors. Additionally, the expression of three key genes involved in ROS stress was measured via RT-PCR. Levels of intracellular ROS measured by DCFDA after ClO2 treatment were significantly higher than those found after treatment in NaClO. Additionally, NaClO treatment resulted in upregulation of ROS-defense genes, while expression of the same genes was typically at base levels or downregulated after ClO2 treatment. As the concentrations of both treatments increased, the NADP+:NADPH ratio shifted to the cofactor being predominantly present as NADP+. These data indicate that ClO2 and NaClO damage E. coli O157:H7 via measurably different mechanisms and that ClO2 does not appear to cause substantial oxidative stress to E. coli O157:H7 directly.

Mechanical Wiping Increases the Efficacy of Liquid Disinfectants on SARS-CoV-2

High-touch environmental surfaces are acknowledged as potential sources of pathogen transmission, particularly in health care settings where infectious agents may be readily abundant. Methods of disinfecting these surfaces often include direct application of a chemical disinfectant or simply wiping the surface with a disinfectant pre-soaked wipe (DPW). In this study, we examine the ability of four disinfectants, ethanol (EtOH), sodium hypochlorite (NaOCl), chlorine dioxide (ClO2), and potassium monopersulfate (KMPS), to inactivate SARS-CoV-2 on a hard, non-porous surface, assessing the effects of concentration and contact time. The efficacy of DPWs to decontaminate carriers spiked with SARS-CoV-2, as well as the transferability of the virus from used DPWs to clean surfaces, is also assessed. Stainless steel carriers inoculated with approximately 6 logs of SARS-CoV-2 prepared in a soil load were disinfected within 5 min through exposure to 66.5% EtOH, 0.5% NaOCl, and 1% KMPS. The addition of mechanical wiping using DPWs impregnated with these biocides rendered the virus inactive almost immediately, with no viral transfer from the used DPW to adjacent surfaces. Carriers treated with 100 ppm of ClO2 showed a significant amount of viable virus remaining after 10 min of biocide exposure, while the virus was only completely inactivated after 10 min of treatment with 500 ppm of ClO2. Wiping SARS-CoV-2-spiked carriers with DPWs containing either concentration of ClO2 for 5 s left significant amounts of viable virus on the carriers. Furthermore, higher titers of infectious virus retained on the ClO2-infused DPWs were transferred to uninoculated carriers immediately after wiping. Overall, 66.5% EtOH, 0.5% NaOCl, and 1% KMPS appear to be highly effective biocidal agents against SARS-CoV-2, while ClO2 formulations are much less efficacious.

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

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

Application of essential oils in packaging films for the preservation of fruits and vegetables: A review

Fruits and vegetables are highly perishable in nature. Several factors could affect the quality and shelf life of fruits and vegetables. Packaging materials (usually made up of polymers, proteins, lipids, polysaccharides, etc.,) are incorporated with essential oil (EO) which is high in antimicrobial and antioxidant compounds that can enhance the shelf life of fruits and vegetables without affecting their quality. However, the use of EO for postharvest preservation can alter the organoleptic properties of fresh produce. Exploiting synergistic interactions between several EOs, encapsulation of EO, or combining EO with non-thermal techniques such as irradiation, UV-C, cold plasma, ultrasound, etc., may help in preventing the spoilage of food products at lower concentrations without altering their organoleptic properties. This review aims to discuss the overview and current scenario of packaging film with EO for the preservation of fruit and vegetables. We have also discussed the spoilage mechanism of fruits and vegetables, mode of action of EOs, and the effect of EO with packaging film on antimicrobial and sensory properties of fruits and vegetables.

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.

Recent trends in bacterial decontamination of food products by hurdle technology: A synergistic approach using thermal and non-thermal processing techniques

Researchers are continuously discovering varied technologies for microbial control to ensure worldwide food safety from farm-to-fork. The microbial load and virulence of spoilage causing microorganisms, including bacteria, fungi, yeasts, virus, and protozoa, determines the extent of microbial contamination in a food product. Certain pathogenic microbes can cause food poisoning and foodborne diseases, and adversely affect consumers' health. To erade such food safety-related problems, various traditional and novel food processing methods have been adopted for decades. However, some decontamination techniques bring undesirable changes in food products by affecting their organoleptic and nutritional properties. Combining various thermal and non-thermal food processing methods is an effective way to impart a synergistic effect against food spoilage microorganisms and can be used as an alternative way to combat certain limitations of food processing technologies. The combination of different techniques as hurdles put the microorganisms in a hostile environment and disturbs the homeostasis of microorganisms in food temporarily or permanently. Optimization and globalization of these hurdle combinations is an emerging field in the food processing sector. This review gives an overview of recent inventions in hurdle technology for bacterial decontamination, combining different thermal and non-thermal processing techniques in various food products.

Effect of Chlorine Dioxide Treatment on Human Pathogens on Iceberg Lettuce

In the vegetable processing industry, the application of chlorine dioxide (ClO2) as a disinfectant solved in washing water to eliminate undesirable microorganisms harmful to consumers' health and the shelf life of produce has been discussed for years. The disinfection efficacy depends on various factors, e.g., the location of microorganisms and the organic load of the washing water. The present study analyzed the sanitation efficacy of various concentrations of water-solved ClO2 (cClO2: 20 and 30 mg L-1) on Escherichia coli (1.1 × 104 cfu mL-1), Salmonella enterica (2.0 × 104 cfu mL-1) and Listeria monocytogenes (1.7 × 105 cfu mL-1) loads, located on the leaf surface of iceberg lettuce assigned for fresh-cut salads. In addition, it examined the potential of ClO2 to prevent the cross-contamination of these microbes in lettuce washing water containing a chemical oxygen demand (COD) content of 350 mg L-1 after practice-relevant washing times of 1 and 2 min. On iceberg leaves, washing with 30 mg L-1 ClO2 pronouncedly (1 log) reduced loads of E. coli and S. enterica, while it only insignificantly (<0.5 × log) diminished the loads of L. monocytogenes, irrespective of the ClO2 concentration used. Although the sanitation efficacy of ClO2 washing was only limited, the addition of ClO2 to the washing water avoided cross-contamination even at high organic loads. Thus, the application of ClO2 to the lettuce washing water can improve product quality and consumer safety.

Analysis of Biofilm Formation on the Surface of Organic Mung Bean Seeds, Sprouts and in the Germination Environment

This study aimed to analyse the impact of sanitation methods on the formation of bacterial biofilms after disinfection and during the germination process of mung bean on seeds and in the germination environment. Moreover, the influence of Lactobacillus plantarum 299v on the growth of the tested pathogenic bacteria was evaluated. Three strains of Salmonella and E. coli were used for the study. The colony forming units (CFU), the crystal violet (CV), the LIVE/DEAD and the gram fluorescent staining, the light and the scanning electron microscopy (SEM) methods were used. The tested microorganisms survive in a small number. During germination after disinfection D2 (20 min H₂O at 60 °C, then 15 min in a disinfecting mixture consisting of H₂O, H₂O₂ and CH₃COOH), the biofilms grew most after day 2, but with the DP2 method (D2 + L. plantarum 299v during germination) after the fourth day. Depending on the method used, the second or fourth day could be a time for the introduction of an additional growth-limiting factor. Moreover, despite the use of seed disinfection, their germination environment could be favourable for the development of bacteria and, consequently, the formation of biofilms. The appropriate combination of seed disinfection methods and growth inhibition methods at the germination stage will lead to the complete elimination of the development of unwanted microflora and their biofilms.

Effects of Chlorine Dioxide on Oral Hygiene - A Systematic Review and Meta-analysis

Background

Effective and selective oral rinses are required in the daily medical and dental practice. Currently mouthwashes used have substantial side effects.

Objectives

Our aim was to evaluate the efficacy of chlorine dioxide-containing mouthwashes in comparison with other previously established mouth rinses in healthy adults using oral hygiene indices.

Methods

This work was registered in PROSPERO (CRD42018099059) and carried out using multiple databases and reported according to the PRISMA statement. The search terms used were “chlorine dioxide” AND “oral”, and only randomised controlled trials (RCTs) were included. The primary outcome was the alteration of the plaque index (PI), while the secondary outcomes were the gingival index (GI) and bacterial counts. For the risk of bias assessment, the Cochrane Risk of Bias Tool was used. Statistical analysis for data heterogeneity was performed by Q-value and I²-tests.

Results

364 articles were found in the databases. After the selection process, only five RCTs were eligible for meta-analysis. Data heterogeneity was low. There were no statistical differences in effectiveness between chlorine dioxide and other effective mouth rinses in PI (0.720±0.119 vs 0.745±0.131; 95%; confidence intervals (CIs): 0.487-0.952 vs 0.489-1.001, respectively) and GI (0.712±0.130 vs 0.745±0.131; 95% CIs: 0.457–0.967 vs 0.489–1.001, respectively) and also in bacterial counts.

Conclusion

Chlorine dioxide reduces both plaque and gingival indices and bacterial counts in the oral cavity similar to other routinely used oral rinses, however, the evidence supporting this outcome is very limited. Therefore, further large scale RCTs are needed to decrease the risk of bias.

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.

Combined effects of ultrasound and aqueous chlorine dioxide treatments on nitrate content during storage and postharvest storage quality of spinach (Spinacia oleracea L.)

The objectives of this study were to optimize the condition of ultrasonic treatment combined with aqueous chlorine dioxide (ClO₂) on nitrate content of spinach by response surface methodology (RSM), and determine the effectiveness of ultrasound (US) and ClO₂ alone and in combination, on spinach postharvest quality during 7 days' storage period. The optimal treatment parameters obtained were ultrasonic power (300 W), ClO₂ concentration (50 ppm), treatment time (4 min). The combined treatments significantly reduced the nitrate content and maintained better storage quality in terms of total soluble solids (TSS) and ascorbic acid content compared with the individual treatment or untreated. For Chlorophyll content, the combined treatment was significantly higher than the control and ClO₂ treatment, but lower than ultrasonic treatment. The results demonstrated that US combined with ClO₂ are promising alternatives for the reduction of nitrate content, as well as preserving the quality of stored leafy vegetables.

Analysis of flavor and taste attributes differences treated by chemical preservatives: a case study in strawberry fruits treated by 1-methylcyclopropene and chlorine dioxide

Flavor and taste attributes of fruits varied by different preservatives treatments. Changes in sugars, organic acids, amino acids as well as volatiles of strawberries treated with 1-methylcyclopropene (1-MCP) and/or chlorine dioxide (ClO₂) were evaluated during storage period in this study. Our results revealed that the decreases of tartaric acid, malic acid, citric acid, titratable acidity (TA), sucrose and soluble sugar contents were significantly inhibited by 1-MCP + ClO₂. The fructose and glucose contents of all groups remained stable and slightly increased at the last period of 10 days. However, different treatments had no influence on content of succinic acid. Moreover, the highest sweet taste (77.37 mg 100 g^-1 fresh weight) and lowest bitter taste (3.44 mg 100 g^-1 fresh weight) free amino acids (FAA) were observed in the strawberries treated by 1-MCP combined with ClO₂ treatment as compared to other treatments and control. (E)-2-hexenal was the most abundant volatile and showed a significant increase trend during strawberry storage. More interestingly, ethyl butyrate, fruit-like aroma, could be recovered in content by 1-MCP, ClO₂ alone and their combination treatment. Compared with other treatments, the significant different flavor in ClO₂ treatment was identified by principle component analysis. In addition, methyl hexanoate and 4-methoxy-2,5-dimethylfuran-3(2H)-one (DMMF) were the major factors that affected the volatile organic compounds (VOCs) of strawberries through the whole storage. Taken together, 1-MCP coupled with ClO₂ could be a complex preservative to maintain strawberries quality by regulating the flavor and taste attributes.

Inactivation of fungal spores in water using ozone: Kinetics, influencing factors and mechanisms

Fungal contamination of drinking water sources is increasingly threatening the environment and human health. In this study, the inactivation of three genera of dominant fungi in drinking water sources using ozone was first reported. The inactivation of the fungal spores by ozone could be divided into two distinct stages: first a rapid reduction in survival, and then the inactivation at a slower rate. The secondary stage inactivation fitted the Chick-Watson model well, and there was no significant difference in the second-order inactivation rate constants of the three fungal spores (0.199-0.209 L mg^-1 min^-1). The inactivation rate constants of fungal spores by molecular ozone were much lower than those of viruses, which were equivalent to that of Cryptosporidium. The increase in pH and temperature showed a positive effect on the inactivation rate. Damage to cell membranes, leakage of intracellular compounds, and changes of reactive oxygen species and esterase activity in the spores were detected after inactivation. The results indicated that ozone inactivated fungal spores by firstly destroying cell walls and membranes and then causing the release of intracellular compounds. The fungicidal efficiency of ozone was superior to those of chlorine and chlorine dioxide. In addition, the inactivation efficiency of ozone on fungal spores in real water matrices was reduced to 50.7-91.2% of the efficiency in phosphate buffer. In conclusion, ozone showed high efficiency in the inactivation of fungal spores and could be used as an alternative disinfectant for fungal contamination in drinking water sources.

Effectiveness of Aqueous Chlorine Dioxide in Minimizing Food Safety Risk Associated with Salmonella, E. coli O157:H7, and Listeria monocytogenes on Sweet Potatoes

Sodium hypochlorite (NaOCl) is a commonly used sanitizer in the produce industry despite its limited effectiveness against contaminated human pathogens in fresh produce. Aqueous chlorine dioxide (ClO₂) is an alternative sanitizer offering a greater oxidizing potency with greater efficacy in reducing a large number of microorganisms. We investigated the effect of aqueous chlorine dioxide treatment against human pathogens, Salmonella, Escherichia coli O157:H7, and Listeria monocytogenes seeded on sweet potatoes. Sweet potatoes were spot inoculated (4.2 to 5.7 log CFU/cm²) with multi-strain cocktails of Salmonella spp., E. coli O157:H7, and L. monocytogenes and treated for 10–30 min with 5 ppm aqueous ClO₂ or water. Aqueous ClO₂ treatment was significantly (p < 0.05) effective in reducing Salmonella with a reduction of 2.14 log CFU/cm² within 20 min compared to 1.44 log CFU/cm² for water treatment. Similar results were observed for L. monocytogenes with a 1.98 log CFU/cm² reduction compared to 0.49 log CFU/cm² reduction observed after 30 min treatment with aqueous ClO₂ the water respectively. The maximum reduction in E. coli O157: H7 reached 2.1 Log CFU/cm² after 20 min of treatment with aqueous ClO₂. The level of the pathogens in ClO₂ wash solutions, after the treatment, was below the detectable limit. While in the water wash solutions, the pathogens’ populations ranged from 3.47 to 4.63 log CFU/mL. Our study indicates that aqueous ClO₂ is highly effective in controlling cross-contamination during postharvest washing of sweet potatoes.

Integrity of the Escherichia coli O157:H7 Cell Wall and Membranes After Chlorine Dioxide Treatment

Treatments of wastewater and fresh produce commonly employ chlorine as an antimicrobial. However, there are increasing levels of concerns regarding the safety and antimicrobial efficacy of chlorine treatments. Numerous studies have reported the antimicrobial properties of chlorine dioxide (ClO₂) treatment in a variety of applications but information regarding how ClO₂ affects bacteria is limited. In the present study, a mixed-method approach utilizing both quantitative and qualitative methodologies was used to observe Escherichia coli O157:H7 membrane damage after exposure to ClO₂ (2.5, 5, or 10 mg/L) for 5, 10, or 15 min. For comparison, controls of 0.1% peptone, 70% isopropanol, and 10 mg/L NaOCl were applied for 15 min. After treatment, cells were enumerated on selective media overlaid with non-selective media and simultaneously analyzed for damage using the following fluorescent probes (1) Bis-(1,3-Dibutylbarbituric Acid) trimethine oxonol (DiBAC4(3)) for membrane polarization, (2) SYTO 9/propidium iodide (LIVE/DEAD) for membrane permeability, (3) 2-(N-(7-Nitrobenz-2-oxa-1,3-diazol-4-yl)Amino)-2-Deoxyglucose (2-NBDG) for active glucose uptake, and (4) lipid peroxidation through accumulation of malondialdehyde (MDA). Bacterial log reductions after ClO₂ treatment ranged from 0.2 to 5.5 and changes in relative fluorescence units after membrane permeability and glucose uptake assays were not consistent with viability, indicating membrane permeability and metabolism were not substantially altered. Depolarization was observed after NaOCl treatment, however, the polarity of cells treated with ClO₂ were like those treated with water (P < 0.05). Accumulation of MDA was detected only after 10 mg/L ClO₂ treatments, indicating that membrane peroxidation occurred at higher concentrations. Transmission electron microscopy imaging revealed that separation of the cell wall from the cytosol occurred after the 10 mg/L ClO₂ treatment, but the cell wall itself appeared to be unbroken. These data suggest that ClO₂ damage to E. coli O157:H7 is not primarily located at the cell wall and harms cells significantly different than NaOCl at comparable concentrations.

Effect of chlorine dioxide and phosphates on the quality of tiger frog (Rana tigrina) meat during 4 °C storage

Tiger frog (Rana tigrina) meat is extremely perishable. This study investigated the antimicrobial efficacy of chlorine dioxide (ClO₂ ) on frog meat, optimized the formulation of a phosphate-based enhancement solution by response surface methodology (RSM), and determined the quality parameters (i.e., total aerobic counts [TAC], pH, drip loss, cooking loss, color measurements, shear force, total volatile basic nitrogen [TVB-N], and thiobarbituric acid-reactive substances [TBARS]) of refrigerated frog meat pretreated with ClO₂ and the optimized blend of phosphates. Treatments of frog meat with 35 and 70 ppm ClO₂ for 3, 5, and 10 min achieved a 0.7-, 0.9- and 0.9-, and 0.8-, 1.4- and 1.6-log CFU/g reduction of TAC, respectively, indicating the antimicrobial efficacy of ClO₂ was concentration- and time-dependent with such that higher concentrations and/or longer exposure time achieved greater bacterial reductions. The concentrations of the phosphates, including sodium tripolyphosphate (STPP), sodium pyrophosphate (SPP), and sodium hexametaphosphate (SHMP), were optimized as the formula of 0.3% STPP and 0.45% SPP obtaining the highest water retention of the frog meat. After washed with 70 ppm ClO₂ for 10 min and subsequently soaked with 0.3% STPP and 0.45% SPP for 30 min, the frog meat stored at 4 °C shown significantly (P < 0.05) lower TAC (<4.4 log CFU/g) and higher water holding capacity during the whole storage of 12 days, compared to the control. Results indicated that the two-step process may be applicable to slow down deterioration and maintain quality frog meat during refrigeration. PRACTICAL APPLICATION: This research provides a means to slow down deterioration, maintain quality frog meat, and improve stability during refrigeration. Refrigerated frog meat products, which are preferred by consumers with juicier and more tender texture compared to the frozen-thawed meat, could be developed by the frog industry based on the data from this study.

Preparation of Coated Corrugated Box for Controlled-Release of Chlorine Dioxide and Its Application in Strawberry Preservation

Chlorine dioxide (ClO2) has received great attention as a nontoxic and efficient antimicrobial agent for the preservation of fresh fruits and vegetables. A novel two-layer coated corrugated box was developed to release gaseous ClO2 under the trigger of moisture in this study. The inner surface of the box was firstly coated with a mixture of polyvinyl alcohol-NaClO2-diatomite and then with chitosan acetic acid solution. Results showed that ClO2 was successfully released under high humidity due to the reaction of NaClO2, water vapor and acid. The concentration of released ClO2 increased with the increasing NaClO2 content in the coating, while the addition of diatomite stabilized and extended the release. To evaluate the preservation effect, strawberries were packed in the coated box and stored at room temperature. Compared with the control, the decay rate and weight loss of the strawberries packed in the coated box (9 g/L NaClO2) were reduced up to 21.88% and 6.84%, respectively. The surface color, firmness and nutrients content were also better maintained. Therefore, this coated corrugated box with the capability to release ClO2 under the trigger of moisture has great potential to be applied as an antimicrobial packaging for fresh fruits and vegetables.

Antimicrobial action of octanoic acid against Escherichia coli O157:H7 during washing of baby spinach and grape tomatoes

We investigated the antimicrobial efficacy of octanoic acid (OA) against Escherichia coli O157:H7 inoculated on the surface of baby spinach and grape tomatoes during simulated washing processes. 3 mM OA at 45 °C achieved >6 log CFU/g reduction from the surface of tomatoes within 2 min. However, washing baby spinach with 6 mM OA at 5 °C resulted in <1 log CFU/g reduction, highlighting the role of surface properties in inactivation efficacy. OA significantly (p < 0.05) reduced the risk of cross-contamination during washing of spinach as well as tomatoes. Also, total mold and yeast population on surface of spinach was significantly reduced immediately after OA wash and inhibited during following 14 days. Baby spinach and grape tomatoes washed with OA did not cause significant (p > 0.05) difference in color compared to the control and no residual OA was detected in most cases following rinsing of produce in water. OA at the concentrations above 2 mM and temperature higher than 25 °C induced severe membrane damage along with release of ATP and other intracellular constituents resulting in bacterial death. OA can be an attractive natural decontamination agent for washing fresh produce.

Emerging chemical and physical disinfection technologies of fruits and vegetables: a comprehensive review

With a growing demand for safe, nutritious, and fresh-like produce, a number of disinfection technologies have been developed. This review comprehensively examines the working principles and applications of several emerging disinfection technologies. The chemical treatments, including chlorine dioxide, ozone, electrolyzed water, essential oils, high-pressure carbon dioxide, and organic acids, have been improved as alternatives to traditional disinfection methods to meet current safety standards. Non-thermal physical treatments, such as UV-light, pulsed light, ionizing radiation, high hydrostatic pressure, cold plasma, and high-intensity ultrasound, have shown significant advantages in improving microbial safety and maintaining the desirable quality of produce. However, using these disinfection technologies alone may not meet the requirement of food safety and high product quality. Several hurdle technologies have been developed, which achieved synergistic effects to maximize lethality against microorganisms and minimize deterioration of produce quality. The review also identifies further research opportunities for the cost-effective commercialization of these technologies.

Laser Tweezers Raman Spectroscopy (LTRS) to Detect Effects of Chlorine Dioxide on Individual Nosema bombycis Spores

The microsporidium Nosema bombycis (Nb) causes pebrine, a fatal disease in sericulture. Nb is effectively killed by chlorine dioxide (ClO₂); however, the precise killing mechanism remains unclear. We used laser tweezers Raman spectroscopy (LTRS) to monitor the action of ClO₂ on individual Nb spores in real time. Raman peaks of ClO₂ appeared in Nb spores, corresponding to decreased peaks of trehalose that gradually disappeared. A peak (1658 cm^-1) corresponding to the protein α-helix significantly weakened while that (1668 cm^-1) corresponding to irregular protein structures was enhanced; their intensities were negatively correlated in a certain time range and dependent on ClO₂ concentration. The intensities of peaks at 782 cm^-1 (nucleic acids) and 1004 cm^-1 (phenylalanine of protein) did not change evidently even under extremely high ClO₂ concentrations. Thus, ClO₂ rapidly permeates the Nb spore wall, changing the protein secondary structure to lose biological function and destroy permeability, causing trehalose to leak out. These effects are ClO₂ concentration-dependent, but no other obvious changes to biomacromolecules were detected. Single-cell analysis using LTRS is an effective method to monitor the action of chemical sporicides on microbes in real time, providing insight into the heterogeneity of cell stress resistance.

Sprouted Grains: A Comprehensive Review

In the last decade, there has been an increase in the use of sprouted grains in human diet and a parallel increase in the scientific literature dealing with their nutritional traits and phytochemical contents. This review examines the physiological and biochemical changes during the germination process, and the effects on final sprout composition in terms of macro- and micro-nutrients and bioactive compounds. The main factors affecting sprout composition are taken into consideration: genotype, environmental conditions experimented by the mother plant, germination conditions. In particular, the review deepens the recent knowledge on the possible elicitation factors useful for increasing the phytochemical contents. Microbiological risks and post-harvest technologies are also evaluated, and a brief summary is given of some important in vivo studies matching with the use of grain sprouts in the diet. All the species belonging to Poaceae (Gramineae) family as well as pseudocereals species are included.