Disinfection by-products generated by sodium hypochlorite and electrochemical disinfection in different process wash water and fresh-cut products and their reduction by activated carbon

Efficacy of sodium hypochlorite and peracetic acid in reducing cross-contamination during washing of baby spinach at different water quality levels

We evaluated the antimicrobial performance of sodium hypochlorite (NaOCl) and peracetic acid (PAA) during washing of baby spinach in water of varying levels of organic load, as measured by its chemical oxygen demand (COD). Escherichia coli TVS353 was spot inoculated onto one unwashed leaf. Sanitizers were added into water with preadjusted COD (300 or 2500 ppm) to achieve concentrations from 20 to 80 ppm. One inoculated leaf was washed with nine uninoculated leaves in 500 mL water (n = 6). Bacterial load on inoculated leaves was lowered by sanitizers in a dose-dependent manner (p < 0.05) and the lowest bacterial survivor levels were observed at 80 ppm with 2.7 ± 1.2 and 5.1 ± 0.5 Log MPN/leaf for PAA and NaOCl, respectively, at low CODs. PAA was more effective in reducing bacterial load from the inoculated leaf than NaOCl at high CODs (p < 0.05), with 2.9 ± 2.8 and 5.3 ± 0.8 Log MPN/leaf survivors for PAA and NaOCl, respectively. At 80 ppm sanitizer levels, the bacteria was not detected in wash water at any condition but was detected at 20 and 40 ppm at high CODs. The lowest levels of bacteria transferred to uninoculated leaves were observed at 80 ppm sanitizer, at 0.3 ± 0.2 and 0.2 ± 0.1 Log MPN/leaf for PAA and 1.1 ± 1.0 and 0.3 ± 0.3 Log MPN/leaf for NaOCl at low and high CODs, respectively. The log percentage of bacteria transferred ranged from -1.1 at 0 ppm to over -4.5 at 80 ppm, highlighting a reduction in cross-contamination by the sanitizers. PRACTICAL APPLICATION: This study provides effective data on sanitizer usage to fresh produce industry for ensuring food safety during washing of produce. It evaluated the sanitizer effect in a broad range of scenarios including various sanitizer concentrations, and wash water with low and high organic load that is common when recirculating wash water. The results also revealed the differences in two common sanitizers (PAA and NaOCl) in terms of their effectiveness.

Effects of Cross-Resistance of Salmonella Enterica Serovar Enteritidis Induced by Sodium Hypochlorite to Environmental Stress

To investigate the effects of repeated sodium hypochlorite stress on the resistance of Salmonella enterica Serovar Enteritidis (S. Enteritidis) LWCC1051. LWCC1051 was exposed to Trypticase Soy Broth (TSB) containing sodium hypochlorite concentrations of 9 mmol/L, 10 mmol/L, and 11 mmol/L. After 13 repeated transfers and incubations, three sodium hypochlorite resisted LWCC1051 strains were obtained. The D-values and colony morphologies of these strains were assessed. Their survival rates at 60 °C, 65 °C, 70 °C, 75 °C, and - 20 °C were determined and lethality curves at these temperatures were fitted using the Weibull model. Additionally, the Minimal Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC) for these strains in various chemicals, including malic acid, citric acid, ascorbic acid, acetic acid, lactic acid, hydrochloric acid, sodium hydroxide, potassium hydroxide, calcium chloride, sodium chloride, and potassium chloride were ascertained. Sodium hypochlorite concentrations of 9 mmol/L, 10 mmol/L, and 11 mmol/L in TSB induced sodium hypochlorite resistance in S. Enteritidis. D-value increased with the frequency of stress exposure. Higher concentrations of sodium hypochlorite resulted in greater D-values and noticeable differences in colony morphologies. The Weibull model accurately represented the temperature resistance curves of LWCC1051 at the specified temperatures. With increasing sodium hypochlorite stress, both high and low-temperature resistances of LWCC1051 improved. Furthermore, under acetic acid stress, the MIC and MBC values of LWCC1051 strains, post exposure to 9 mmol/L, 10 mmol/L, and 11 mmol/L sodium hypochlorite, doubled. Sodium hypochlorite stress enhances the cross-resistance of LWCC1051 to high temperature, low temperature, and acetic acid treatments.

Anise essential oil immobilized in chitosan microparticles: a novel bactericidal material for food protection

Foodborne infections in humans are one of the major concerns of the food industries, especially for minimally processed foods (MPF). Thereby, the packaging industry applies free chlorine in the sanitization process, ensuring the elimination of any fecal coliforms or pathogenic microorganisms. However, free chlorine's propensity to react with organic matter, forming toxic compounds such as trihalomethanes and haloacetic acid. Therefore, the present work aimed to synthesize a novel organic biomaterial as an alternative to free chlorine. Chitosan microparticles were produced, with Pimpinella anisum (anise) essential oil immobilized in the biopolymer matrix (MPsQTO). The characterization of this biomaterial was done through GC-MS/MS, FT-IR, and SEM. Antimicrobial assays proved that the MPsQTO presented antibacterial activity for Escherichia coli, Salmonella typhi, Pseudomonas aeruginosa, and Bacillus subtilis at 300 µL mL-1 of concentration. The fluorescence microscope also showed the MPsQTO targets the cytoplasmatic membrane, which is responsible for cell death in the first minutes of contact. Studies with the mutant B. subtilis (amy::pspac-ftsZ-gfpmut1) and the Saccharomyces cerevisiae D7 also proved that the biomaterial did not affect the genetic material and did not have any mutagenic/carcinogenic effect on the cells. The sanitization assays with pumpkin MPF proved that the MPsQTO is more effective than free chlorine, increasing the shelf-life of the MPF. Consequently, the novel biomaterial proposed in this work is a promising alternative to traditional chemical sanitizers.

Advances on electrochemical disinfection research: Mechanisms, influencing factors and applications

Disinfection, a vital barrier against pathogenic microorganisms, is crucial in halting the spread of waterborne diseases. Electrochemical methods have been extensively researched and implemented for the inactivation of pathogenic microorganisms from water and wastewater, primarily owing to their simplicity, efficiency, and eco-friendliness. This review succinctly outlined the core mechanisms of electrochemical disinfection (ED) and systematically examined the factors influencing its efficacy, including anode materials, system conditions, and target species. Additionally, the practical application of ED in water and wastewater treatment was comprehensively reviewed. Case studies involving various scenarios such as drinking water, hospital wastewater, black water, rainwater, and ballast water provided concrete instances of the expansive utility of ED. Finally, coupling ED with other technologies and the resulting synergies were introduced as pivotal foundations for subsequent engineering advancements.

Comparison of the efficacy of physical and chemical strategies for the inactivation of biofilm cells of foodborne pathogens

Biofilm formation is a strategy in which microorganisms generate a matrix of extracellular polymeric substances to increase survival under harsh conditions. The efficacy of sanitization processes is lowered when biofilms form, in particular on industrial devices. While various traditional and emerging technologies have been explored for the eradication of biofilms, cell resistance under a range of environmental conditions renders evaluation of the efficacy of control challenging. This review aimed to: (1) classify biofilm control measures into chemical, physical, and combination methods, (2) discuss mechanisms underlying inactivation by each method, and (3) summarize the reduction of biofilm cells after each treatment. The review is expected to be useful for future experimental studies and help to guide the establishment of biofilm control strategies in the food industry.

Drinking water treatment and associated toxic byproducts: Concurrence and urgence

Reclaimed water is highly required for environmental sustainability and to meet sustainable development goals (SDGs). Chemical processes are frequently associated with highly hazardous and toxic by-products, like nitrosamines, trihalomethanes, haloaldehydes, haloketones, and haloacetic acids. In this context, we aim to summarize the formation of various commonly produced disinfection by-products (DBPs) during wastewater treatment and their treatment approaches. Owing to DBPs formation, we discussed permissible limits, concentrations in various water systems reported globally, and their consequences on humans. While most reviews focus on DBPs detection methods, this review discusses factors affecting DBPs formation and critically reviews various remediation approaches, such as adsorption, reverse osmosis, nano/micro-filtration, UV treatment, ozonation, and advanced oxidation process. However, research in the detection of hazardous DBPs and their removal is quite at an early and initial stage, and therefore, numerous advancements are required prior to scale-up at commercial level. DBPs abatement in wastewater treatment approach should be considered. This review provides the baseline for optimizing DBPs formation and advancements in the remediation process, efficiently reducing their production and providing safe, clean drinking water. Future studies should focus on a more efficient and rigorous understanding of DBPs properties and degradation of hazardous pollutants using low-cost techniques in wastewater treatment.

Nanoscale zero-valent iron/silver@activated carbon-reduced graphene oxide: Efficient removal of trihalomethanes from drinking water

AC-supported nanoscale zero-valent iron composites (nZVI/AC) exhibit significant environmental implications for trihalomethanes (THMs)-contaminated water remediation. To improve the adsorption and degradation capability of AC, herein, a composite (nZVI/Ag@AC-RGO) consisting of AC, reduced graphene oxide (RGO), nanoscale zero-valent iron (nZVI), and silver (Ag) was synthesized and characterized using several techniques, such as scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, N₂ adsorption-desorption isotherms, and X-ray photoelectron spectroscopy (XPS). The analysis of textural and morphological structures showed that a tightly-attached RGO film, amorphous iron, and weak crystal silver nanoparticles with a size of 20-30 nm were evenly immobilized on the support. Specific surface area increased by 19.12% after supporting RGO, while it decreased after supporting nZVI and Ag due to the partial blockage of micropores. The Fe surface was concurrently coated by iron oxides (Fe₂O₃, FeOOH) and Ag. THMs were eliminated through multilayer reaction processes. The values of the adsorption constant (K_F) of chloroform (CHCl₃), dichlorobromoethane (CHBrCl₂), dibromochloroethane (CHBr₂Cl), and tribromomethane (CHBr₃) adsorbed by nZVI/Ag@AC-RGO increased by 34.4, 33.7, 81.6, and 67.3%, respectively, compared to pristine AC. THMs with more Br atoms exhibited better removal efficiency and adsorption capacity, along with a higher oxidation degree of the Fe surface. CHBrCl₂ and CHBr₂Cl mainly decomposed into chloromethane (CH₃Cl) and dichloromethane (CH₂Cl₂), and CHBr₃ and CHCl₃ primarily degraded into dibromomethane (CH₂Br₂) and CH₂Cl₂, respectively, along with generating Cl^- and Br^-. Conclusively, THMs-contaminated water could be remediated by coupling AC pre-enrichment and the reactivity of nZVI/Ag.

A Review of Essential Oils as Antimicrobials in Foods with Special Emphasis on Fresh Produce

ABSTRACT

Consumer safety concerns over established fresh produce washing methods and the demand for organic and clean-label food has led to the exploration of novel methods of produce sanitization. Essential oils (EOs), which are extracted from plants, have potential as clean-label sanitizers because they are naturally derived and act as antimicrobials and antioxidants. In this review, the antimicrobial effects of EOs are explored individually and in combination, as emulsions, combined with existing chemical and physical preservation methods, incorporated into films and coatings, and in vapor phase. We examined combinations of EOs with one another, with EO components, with surfactants, and with other preservatives or preservation methods to increase sanitizing efficacy. Components of major EOs were identified, and the chemical mechanisms, potential for antibacterial resistance, and effects on organoleptic properties were examined. Studies have revealed that EOs can be equivalent or better sanitizing agents than chlorine; nevertheless, concentrations must be kept low to avoid adverse sensory effects. For this reason, future studies should address the maximum permissible EO concentrations that do not negatively affect organoleptic properties. This review should be beneficial to food scientists or industry personnel interested in the use of EOs for sanitization and preservation of foods, including fresh produce.

HIGHLIGHTS

Fresh-Cut Vegetables Processing: Environmental Sustainability and Food Safety Issues in a Comprehensive Perspective

The fresh-cut industry supplies the food market with healthy fresh fruit and vegetables and, in that way, may contribute to improve the nutritional status of the general population. On the other hand, over the last few years increasing concerns have been raised regarding the environmental impact of the fresh-cut industry, human health risks from exposure to disinfection by-products found in fresh-cut products and chlorine-based disinfection treatments during produce processing. This review provides a comprehensive view of the main interlinked aspects related to food safety and environmental impact of processing of fresh-cut vegetables. Advantages and downsides of the mainstream disinfection strategy, based on the use of chlorine-related disinfecting agents, along with some alternative treatments close to a wide commercial application, are discussed. Limitation in the application of these strategies to processing of organic fresh-cut produce are also highlighted, examining the specific environmental and food safety problems in the organic sector. Areas where lack of available information hinders at present a clear understanding of priorities of research and action are pointed out. Innovative conceptual tools are proposed to address these multiple and interlinking issues and to overcome limitations of currently available technologies. A comprehensive and multidisciplinary approach is suggested to move toward a more safe and environmentally sustainable production of fresh-cut products.

Effects of process factors on the performance of electrochemical disinfection for wastewater in a continuous-flow cell reactor

Although electrochemical disinfection has been shown to be an effective approach to inactivate bacteria in saline water, the effects of process parameters and reactor design for its application in low-salinity water have not been well understood. In this study, factorial experiments were performed to investigate the direct and confounded effects of applied current (5-20 mA), contact time (2.5-20 min), anode surface area (185-370 cm²), and chloride concentration (50-400 mg L^-1) on the disinfection efficiency in fresh water and the secondary effluent of municipal wastewater. An electrochemical disinfection reactor cell with an internal volume of 75 cm³ was designed and fabricated. Residence time distribution analysis showed that the internal mixing of the reactor is similar to that of a dispersed plug-flow reactor. All studied process parameters showed significant effect on the kill efficiency, with the applied current and contact time having the most dominant effect. Although the effect of chloride concentration, which is responsible for electrochemical production of free chlorine in water, is statistically significant, it is not as prominent as those reported for high salinity water. A synergistic effect between chloride concentration and anode surface area was identified, leading to high kill efficiency (99.9%, 3 log kill) at low current density (0.0135 mA cm^-2). Response surface modeling results suggested that a scaled-up disinfection reactor can be designed using large anode surface area with long contact time for high chloride water (400 mg L^-1) or high current density with short contact time for low chloride water (50 mg L^-1). The power requirement of a portable system treating 37.85 m³ day^-1 (10,000 gpd) of municipal wastewater was estimated to be 1.9 to 8.3 kW to achieve a 3 log kill, depending on the reactor design.

Evolving challenges and strategies for fungal control in the food supply chain

Fungi that spoil foods or infect crops can have major socioeconomic impacts, posing threats to food security. The strategies needed to manage these fungi are evolving, given the growing incidence of fungicide resistance, tightening regulations of chemicals use and market trends imposing new food-preservation challenges. For example, alternative methods for crop protection such as RNA-based fungicides, biocontrol, or stimulation of natural plant defences may lessen concerns like environmental toxicity of chemical fungicides. There is renewed focus on natural product preservatives and fungicides, which can bypass regulations for 'clean label' food products. These require investment to find effective, safe activities within complex mixtures such as plant extracts. Alternatively, physical measures may be one key for fungal control, such as polymer materials which passively resist attachment and colonization by fungi. Reducing or replacing traditional chlorine treatments (e.g. of post-harvest produce) is desirable to limit formation of disinfection by-products. In addition, the current growth in lower sugar food products can alter metabolic routing of carbon utilization in spoilage yeasts, with implications for efficacy of food preservatives acting via metabolism. The use of preservative or fungicide combinations, while involving more than one chemical, can reduce total chemicals usage where these act synergistically. Such approaches might also help target different subpopulations within heteroresistant fungal populations. These approaches are discussed in the context of current challenges for food preservation, focussing on pre-harvest fungal control, fresh produce and stored food preservation. Several strategies show growing potential for mitigating or reversing the risks posed by fungi in the food supply chain.

Disinfection of Bacteria in Water by Capacitive Deionization

Clean water is one of the primary UN sustainable development goals for 2,030 and sustainable water deionization and disinfection is the backbone of that goal. Capacitive deionization (CDI) is an upcoming technique for water deionization and has shown substantial promise for large scale commercialization. In this study, activated carbon cloth (ACC) electrode based CDI devices are used to study the removal of ionic contaminants in water and the effect of ion concentrations on the electrosorption and disinfection functions of the CDI device for mixed microbial communities in groundwater and a model bacterial strain Escherichia coli. Up to 75 % of microbial cells could be removed in a single pass through the CDI unit for both synthetic and groundwater, while maintaining the salt removal activity. Mortality of the microbial cells were also observed during the CDI cell regeneration and correlated with the chloride ion concentrations. The power consumption and salt removal capacity in the presence and absence of salt were mapped and shown to be as low as 0.1 kWh m⁻³ and 9.5 mg g⁻¹, respectively. The results indicate that CDI could be a viable option for single step deionization and microbial disinfection of brackish water.

Chemical risks associated with ready-to-eat vegetables: quantitative analysis to estimate formation and/or accumulation of disinfection byproducts during washing

Fresh produce can become contaminated with disease‐causing microorganisms and chemical contaminants at every step of the production and processing chain and in a variety of ways, including through contact with contaminated process water. Water quality is critical to prevent microbial and chemical risks in any of the postharvest and processing operations related to fresh and fresh‐cut fruits and vegetables. The wash process requires high volumes of water, which are usually reduced by water reuse. To maintain the microbiological quality of the process water, intervention strategies are needed. Chemical disinfection is the most common method to maintain the microbial quality of process water. However, the use of chemicals leads to the formation/accumulation of disinfection byproducts (DBPs), which can be absorbed by the washed vegetables. This is the case of trihalomethanes (THMs) and chlorates. The presence of high concentrations of DBPs in vegetables has led to an intensive debate on current disinfection practices and how DBPs may enter the food supply chain, becoming a potential health risk for consumers. To assess the risk associated with the formation/accumulation of DBPs in process water, a quantitative analysis was done. Available data have been used to develop mathematical models to predict the formation/accumulation of DBPs (chlorates and THMs) in process water due to the use of chlorine‐derived compounds. Preliminary models have been developed, but adjustments are still needed to refine them. The present study contributes more information related to the development of a mathematical model for the accumulation of chlorates and THMs in process water.