Operational limits of sodium hypochlorite for different fresh produce wash water based on microbial inactivation and disinfection by-products (DBPs)

Enhancing water efficiency in the processing of leafy greens: Efficacy of inline chlorine and pH control systems in reducing microbial contamination and limiting DBP formation

Optimizing water use in the food industry is crucial due to its increasing scarcity. Disinfectants extend the lifespan of wash water by inhibiting bacterial growth and reducing cross-contamination risks. Chlorine is commonly chosen for its affordability, ease of use, and availability. Maintaining a pH of 5.5-6 maximizes free chlorine effectiveness. However, maintaining stable pH and chlorine levels is challenging. Continuous inline monitoring systems for chlorine levels offer significant advantages over offline point measurements, addressing fluctuating chlorine and pH levels. The Automated SmartWash Analytical platform (ASAP) unit, an inline dosing and monitoring (i.e. control) system, was tested at full scale during the washing of iceberg and Lollo Rossa lettuce, using different lettuce-to-water ratios, simulating various processing conditions. Inline and offline free chlorine and pH measurements were compared with those of the ASAP unit. Additional physicochemical parameters, including chemical oxygen demand (COD), ultraviolet absorbance at 254 nm (UVA254), oxidation-reduction potential (ORP), and turbidity, were also monitored. Microbiological analysis (total plate count, coliforms, and Pseudomonas spp.) assessed cross-contamination risks, while trihalomethanes and chlorate levels in wash water and final products were evaluated to monitor DBP. Propylene glycol and orthophosphate, processing aids from SmartWash Original acidulant (i.e.T-128, a chlorine stabilizer), were also measured. Results demonstrated the control unit's ability to maintain stable chlorine and pH levels despite increasing organic loads, reducing cross-contamination risks and ensuring microbiological stability. DBP levels and processing aids remained within legal limits in the final product. Moreover, the sensory quality of fresh-cut lettuce was unaffected, regardless of chlorine use.

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.

Depletion of Free Chlorine and Generation of Trichloromethane in the Presence of pH Control Agents in Chlorinated Water at pH 6.5

Chlorine is commonly used by the fresh produce industry to sanitize water and minimize pathogen cross-contamination during handling. The pH of chlorinated water is often reduced to values of pH 6-7, most commonly with citric acid to stabilize the active antimicrobial, hypochlorous acid (a form of free chlorine). Previous studies have demonstrated that citric acid reacts with chlorine to form trichloromethane, a major chlorine by-product in water and a potential human carcinogen. However, it is unclear if other pH control agents could be used in the place of citric acid to minimize the formation of trichloromethane. The objective of the present study was to determine the reactivity of organic and inorganic pH control agents, with chlorine, to generate trichloromethane. Free chlorine (∼100 mg/L) was mixed with 10 mM of each of twelve organic acids and two inorganic pH control agents (i.e., sodium acid sulfate and phosphoric acid) to effect a pH level of 6.5. Free chlorine and trichloromethane levels were measured over 3 h at 3 and 22°C. Results demonstrated that ascorbic acid, dehydroascorbic acid, citric acid, and malic acid rapidly depleted free chlorine concentrations at both 22°C and 3°C, while tartaric acid and lactic acid decreased chlorine concentrations more slowly. Other pH control agents did not significantly reduce free chlorine either at 22 or 3°C. Citric acid led to the generation of significantly higher concentrations of trichloromethane than did other acids. Chloroacetone was also found in chlorinated water in the presence of citric acid and ascorbic acid. Taking buffering capacity and pKa values into account, phosphoric acid and some organic acids may be used to replace citric acid as pH control agents in chlorinated water for washing fresh produce, to stabilize free chlorine level and reduce the generation of trichloromethane.

Evaluating the Potential of Ozone Microbubbles for Inactivation of Tulane Virus, a Human Norovirus Surrogate

This study investigated the efficacy of low-dose ozone microbubble solution and conventional aqueous ozone as inactivation agents against Tulane virus samples in water over a short period of time. Noroviruses are the primary cause of foodborne illnesses in the US, and the development of effective inactivation agents is crucial. Ozone has a high oxidizing ability and naturally decomposes to oxygen, but it has limitations due to its low dissolution rate, solubility, and stability. Ozone microbubbles have been promising in enhancing inactivation, but little research has been done on their efficacy against noroviruses. The study examined the influence of the dissolved ozone concentration, inactivation duration, and presence of organic matter during inactivation. The results showed that ozone microbubbles had a longer half-life (14 ± 0.81 min) than aqueous ozone (3 ± 0.35 min). After 2, 10, and 20 min postgeneration, the ozone concentration of microbubbles naturally decreased from 4 ppm to 3.2 ± 0.2, 2.26 ± 0.19, and 1.49 ± 0.23 ppm and resulted in 1.43 ± 0.44, 0.88 ± 0.5, and 0.68 ± 0.53 log10 viral reductions, respectively, while the ozone concentration of aqueous ozone decreased from 4 ppm to 2.52 ± 0.07, 0.43 ± 0.05, and 0.09 ± 0.01 ppm and produced 0.8 ± 0.28, 0.29 ± 0.41, and 0.16 ± 0.21 log10 reductions against Tulane virus, respectively (p = 0.0526), suggesting that structuring of ozone in the bubbles over the applied treatment conditions did not have a significant effect, though future study with continuous generation of ozone microbubbles is needed.

Optimization of a ultra-high-pressure liquid chromatography-tandem multiple reaction monitoring mass spectrometry method for monitoring haloacetic acids as chlorinated disinfection by-products in the fresh-cut industry

Haloacetic acids (HAAs) are one of the most important chlorinated disinfection by-products generated during water disinfection in the fresh-cut industry, and they can remain in the product, resulting in a consumer health risk. In this study, ultra-high-pressure liquid chromatography-tandem multiple reaction monitoring mass spectrometry (UHPLC-MRM) analysis used for drinking water was optimized and applied for the quantification of nine HAAs (HAA9) in fresh-cut lettuce and process water samples, with the complex matrix interferences for separation, and quantification problems. The method showed good selectivity, specificity and linearity, satisfactory values for trueness (recoveries of 80-116 %), precision (<22 %), and uncertainty (<55 %). Quantification limits varied from 1 to 5 µg L-1 or µg kg-1. The matrix effect for tribromoacetic, bromochloroacetic and chlorodibromoacetic acid was corrected by matrix-matched calibration and standard addition. After storage at -20 °C, only monobromoacetic acid was the HAA which loss happened after 7 days. The application of the methodology in lettuce and process water samples from the industry was successfully implemented. Therefore, this method could be employed for the quality control and regulatory analysis of HAAs in fresh products and process water from the fruit and vegetable industry.

Effect of peeling, cutting, or shredding of lettuce, carrot, or potato on the efficacy of chlorine disinfection

Minimally processed vegetables are washed and subsequently disinfected by immersion in water solutions with antimicrobials which reduce the initial pathogenic or spoilage microbial load. Chlorine remains one of the most widely used disinfectants for vegetables and hence the importance of studying its properties. The aim of this study was to evaluate the effect of peeling, cutting, and shredding on the effectiveness of chlorine (200 ppm) as a disinfectant in lettuce, carrot, and potato. Three independent repetitions of each experiment were completed, and data was statistically analyzed. Results showed that the maintenance of the chlorine concentration in the disinfectant solution, over time, depended on the vegetables' preliminary processing technique (whole, peeled, cut, or shredded) (p < 0.05). In general, the disinfection treatments studied reduced Escherichia coli by 1-8 logs. The addition of chlorine in the disinfectant solution allowed greater reduction in E. coli than using water immersions (p < 0.05) and disinfection times longer than 5 min did not improve these microbiological reductions (p>0.05). The vegetables' subdivision (whole, peeled, cut, or shredded) can affect both E coli's reduction and the vegetables' residual chlorine concentration. No trend was observed in terms of sensory differences and their relationship to the vegetables' processing and disinfection. These results suggest that each facility must validate its disinfection processes, according to the conditions established on site and reduction goals related to initial microbial counts, vegetables' quality, processing operations, and other important aspects.

Microbiological hazards associated with the use of water in the post-harvest handling and processing operations of fresh and frozen fruits, vegetables and herbs (ffFVHs). Part 1 (outbreak data analysis, literature review and stakeholder questionnaire)

The contamination of water used in post-harvest handling and processing operations of fresh and frozen fruit, vegetables and herbs (ffFVHs) is a global concern. The most relevant microbial hazards associated with this water are: Listeria monocytogenes, Salmonella spp., human pathogenic Escherichia coli and enteric viruses, which have been linked to multiple outbreaks associated with ffFVHs in the European Union (EU). Contamination (i.e. the accumulation of microbiological hazards) of the process water during post-harvest handling and processing operations is affected by several factors including: the type and contamination of the FVHs being processed, duration of the operation and transfer of microorganisms from the product to the water and vice versa, etc. For food business operators (FBOp), it is important to maintain the microbiological quality of the process water to assure the safety of ffFVHs. Good manufacturing practices (GMP) and good hygienic practices (GHP) related to a water management plan and the implementation of a water management system are critical to maintain the microbiological quality of the process water. Identified hygienic practices include technical maintenance of infrastructure, training of staff and cooling of post-harvest process water. Intervention strategies (e.g. use of water disinfection treatments and water replenishment) have been suggested to maintain the microbiological quality of process water. Chlorine-based disinfectants and peroxyacetic acid have been reported as common water disinfection treatments. However, given current practices in the EU, evidence of their efficacy under industrial conditions is only available for chlorine-based disinfectants. The use of water disinfection treatments must be undertaken following an appropriate water management strategy including validation, operational monitoring and verification. During operational monitoring, real-time information on process parameters related to the process and product, as well as the water and water disinfection treatment(s) are necessary. More specific guidance for FBOp on the validation, operational monitoring and verification is needed.

Assessment of eco-toxic effects of commonly used water disinfectant on zebrafish (Danio rerio) swimming behaviour and recovery responses: an early-warning biomarker approach

Eco-toxicity profiles for commonly used disinfectants were lacking. Available traditional toxicity techniques have some limitations (assessments and ethical issues). Behaviour toxicology is a promising research area towards early warning and non-invasive approaches. We studied the potential eco-toxic effects of sodium hypochlorite (NaOCl) on the swimming behaviour of zebrafish. Zebrafish were exposed to different concentrations (Treatment I, Treatment II, Treatment III, and Treatment IV) of NaOCl for 360 h. Recovery study (144 h) was conducted for NaOCl treatment groups. The swimming behaviour of zebrafish was quantified efficiently using an online monitoring system (OMS). OMS dataset was processed for determination of behavioural differences by MATLAB and SPSS. Compared to the control group, the swimming strength of zebrafish under NaOCl treatments declined significantly (p < 0.001). Avoidance behaviour has occurred on zebrafish under NaOCl exposure periods. Furthermore, NaOCl toxicity also adjusted circadian rhythms on zebrafish. Zebrafish swimming strength was significantly (p < 0.001) improved under-recovery periods. Moreover, normal diurnal patterns have occurred. NaOCl could cause behavioural abnormalities in non-target organisms. Continuous exposure to common disinfectants could cause external and internal stress on non-target organisms, resulting in behavioural changes and circadian rhythm adjustments. Continuous changes in behavioural and circadian rhythms might reduce organisms' fitness and adaptation capacity. This study highlights (1) the importance of computer-based toxicity assessments, and (2) swimming behaviour is an early warning biomarker for eco-toxicity studies.

Formation of Oleic Acid Chlorohydrins in Vegetables during Postharvest Chlorine Disinfection

High chlorine doses (50-200 mg/L) are used in postharvest washing facilities to control foodborne pathogen outbreaks. However, chlorine can react with biopolymers (e.g., lipids) within the produce to form chlorinated byproducts that remain in the food. During chlorination of micelles of oleic acid, an 18-carbon alkene fatty acid, chlorine added rapidly across the double bond to form the two 9,10-chlorohydrin isomers at a 100% yield. The molar conversion of lipid-bound oleic acid to 9,10-chlorohydrins in chlorine-treated glyceryl trioleate and produce was much lower, reflecting the restricted access of chlorine to lipids. Yields from spinach treated with 100 mg/L chlorine at 7.5 °C for 2 min increased from 0.05% (0.9 nmol/g-spinach) for whole leaf spinach to 0.11% (2 nmol/g) when shredding increased chlorine access. Increasing temperature (21 °C) and chlorine contact time (15 min) increased yields from shredded spinach to 0.83% (22 nmol/g) at 100 mg/L chlorine and to 1.8% (53 nmol/g) for 200 mg/L chlorine. Oleic acid 9,10-chlorohydrin concentrations were 2.4-2.7 nmol/g for chlorine-treated (100 mg/L chlorine at 7.5 °C for 2 min) broccoli, carrots, and butterhead lettuce, but 0.5-1 nmol/g for cabbage, kale, and red leaf lettuce. Protein-bound chlorotyrosine formation was higher in the same vegetables (5-32 nmol/g). The Chinese hamster ovary cell chronic cytotoxicity LC₅₀ value for oleic acid 9,10-chlorohydrins was 0.106 mM. The cytotoxicity associated with the chlorohydrins and chlorotyrosines in low masses (9-52 g) of chlorine-washed vegetables would be comparable to that associated with trihalomethanes and haloacetic acids at levels of regulatory concern in drinking water.

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.

Assessment of the di- and tri-chlorinated haloacetic acids during broiler prechilling

Sodium hypochlorite (NaClO) has been widely used at 100 ppm concentration during poultry slaughter to reduce carcass microorganism loads. However, its use in poultry processing is restricted owing to the potential risks of disinfection by-products (DBPs) that can be produced by the reaction of NaClO with poultry meat components. This study assessed whether dichloroacetic acid (DCAA) and trichloroacetic acid (TCAA), as primary DBP representatives, were produced when NaClO was used as a disinfectant in various methods during broiler prechilling. Headspace gas chromatography-mass spectrometry for the quantitative determination of DCAA and TCAA in 180 prechilling water samples and 30 broiler meat samples, obtained from large standard slaughterhouses equipped with an online monitoring system to control the NaClO concentration between 50 and 100 ppm, showed that neither DCAA nor TCAA were detected. In simulation assays, haloacetic acids (HAAs) were not detected when the concentration of the NaClO solution was less than 200 ppm with low frequency addition; however, more than 0.1 mg/L of DCAA and TCAA were detected on applying 200, 300, 400, 500, and 1000 ppm NaClO at high frequency. These findings indicated that adding high concentrations of NaClO and frequently adding low levels pose a potential risk of DBP formation. This investigation provides a basis for the establishment of food risk and the scientific use of NaClO in poultry processing, and contributes to the evaluation of DBPs in poultry slaughter. PRACTICAL APPLICATION: This study confirmed the occurrences of DCAA and TCAA during broiler chilling processing, indicating that formation of HAAs in simulation systems was correlated with NaClO levels and validated the absence of DCAA and TCAA with less than 200 ppm, providing a basic study for food safety standards and regulations on the disinfectants used in food processing.

Comparison of Peracetic Acid and Chlorine Effectiveness during Fresh-Cut Vegetable Processing at Industrial Scale

ABSTRACT

This study was conducted to compare the efficacy of two sanitizing agents, chlorine and peracetic acid (PAA), in reducing spoilage and pathogenic microorganisms and disinfection by-products in the washing stage of three types of minimally processed vegetables: iceberg lettuce, carrots, and baby leaves. These fresh-cut products are consumed uncooked; thus, proper sanitation is essential in preventing foodborne illness outbreaks. The comparison was done at industrial scale with equipment already used in the fresh-cut industry and with washers designed and manufactured for this purpose. Results showed that for washing water hygiene and final product microbial quality, the use of PAA or chlorine had similar efficacy. Different scenarios combining PAA, chlorine, and water were tested, simulating the current industrial processes for each of the tested vegetables. Overall, results confirmed that the use of a sanitizer, PAA or chlorine, in the washing water is effective for the prevention of cross-contamination during the washing process and hence for produce food safety. For final product microbiological quality and shelf life, the use of chlorine or PAA showed no significant differences in lettuce or baby leaves. Chlorinated disinfection by-products in processing water were not formed in significant amounts when washing water was treated with PAA in all scenarios and for all tested vegetables, whereas washing with chlorine (80 mg/L) generated important amounts of trihalomethanes, chlorates, and chlorites. Although chlorates and chlorites were always below the recommended levels or legal limits established for drinking water, trihalomethanes exceeded the legal limits. For perchlorates, values were below the quantification limit in all scenarios. Our results show that PAA is a reliable alternative to chlorine disinfection strategies in the fresh-cut industry.

HIGHLIGHTS

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.

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.