Guidelines To Validate Control of Cross-Contamination during Washing of Fresh-Cut Leafy Vegetables

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.

Fresh-cut watermelon: postharvest physiology, technology, and opportunities for quality improvement

Watermelon (Citrullus lanatus L.) fruit is widely consumed for its sweetness, flavor, nutrition and health-promoting properties. It is commonly commercialized in fresh-cut format, satisfying consumer demand for freshness and convenience, but its shelf-life is limited. Despite the potential for growth in fresh-cut watermelon sales, the industry faces the challenge of maintaining quality attributes during storage. Fresh-cut processing induces a series of physiological and biochemical events that lead to alterations in sensory, nutritional and microbiological quality. A signal transduction cascade involving increases in respiration and ethylene production rates and elevated activities of cell wall and membrane-degrading enzymes compromise cellular and tissue integrity. These responses contribute to the development of quality defects like juice leakage, firmness loss and water-soaked appearance. They also drive the loss of bioactive compounds like lycopene, affecting flesh color and reducing nutritional value, ultimately culminating in consumer rejection, food losses and waste. Although great research progress has been achieved in the past decades, knowledge gaps about the physiological, biochemical and molecular bases of quality loss persist. This review article summarizes the advances in the study of physicochemical, microbiological, nutritional, and sensory changes linked to the deterioration of watermelon after processing and during storage. Different technological approaches for quality improvement and shelf-life extension are summarized: pre- and postharvest, physical, and chemical. We also discuss the advantages, disadvantages and challenges of these interventions and propose alternative directions for future research aiming to reduce qualitative and quantitative fresh-cut watermelon losses.

Efficacy of Air and Oxygen Micro-nano Bubble Waters Against Colletotrichum gloeosporioides and Impacts on Postharvest Quality of 'Fan Retief' Guava Fruit

This study focused on the application of micro-nano bubbles (MNBs) water generated using air or oxygen (O2), as an alternative to chlorine-based wash for fruits. For the in vitro and in vivo investigation, 106 spore or conidia/mL Colletotrichum gloeosporioides suspension was used, and treated with solutions of air- or O2-MNB for 30- or 60-min, sodium hypochlorite (NaOCl), and untreated (as control). In the second experiment, freshly harvested guava fruits were washed with tap water (control), NaOCl (standard practice), air-, or O2-MNB (for 15- or 30-min). All samples were packaged, stored for 21 days at 13 °C, and monitored for changes in natural microbial population and quality attributes. Based on the confocal laser and transmission electron microscopy results, exposure of C. gloeosporioides to air-MNB for 60 min resulted in the lowest viable cell count (%) compared to control and other treatments (O2-MNB and NaOCl). Air- and O2-MNB treatments damaged cellular structures, disrupted cell membrane integrity, and deformed hyphal morphology. Washing 'Fan Retief' guava (Psidium guajava L.) in air- or O2-MNB (for 15 and/or 30 min), better-retained tissue strength, delayed changes in color, and total soluble solid (TSS) content. Notably, MNB treatments were as effective as NaOCl washing and significantly reduced microbial load on fruit surface by ≥2 Log (p < 0.05). Micro-nano bubble water treatment offers a new paradigm for decontamination and preservation of guava fruit quality.

Development of a Flexible Produce Supply Chain Food Safety Risk Model: Comparing Tradeoffs Between Improved Process Controls and Additional Product Testing for Leafy Greens as a Test Case

The produce industry needs a tool to evaluate food safety interventions and prioritize investments and future research. A model was developed in R for a generic produce supply chain and made accessible via Shiny. Microbial contamination events, increases, reductions, and testing can be modeled. The output for each lot was the risk of one, 300-gram sample testing positive, described by two industry-relevant risk metrics, the overall risk of a positive test (proxy for recall risk) and the number of lots with the highest risk (>1 in 10 chance) of testing positive (proxy for public health risk). A leafy green supply chain contaminated with Shiga-toxin-producing Escherichia coli was modeled with a mean of 1 pathogen cell per pound (µ = 1 CFU/lb or -2.65 Log(CFU/g)) under high (σ = 0.8 Log(CFU/g)) and low (σ = 0.2 Log(CFU/g)) variability. Baseline risk of a positive test in the low-variability scenario (1 in 20,000) was lower than for high-variability (1 in 4,500), showing rare high-level contamination drives risk. To evaluate tradeoffs, we modeled two well-studied, frequently used interventions: additional product testing (8 of 375-gram tests/lot) and improved process controls (additional -0.87 ± 0.32 Log(CFU/g) reduction). Improved process controls better-reduced recall risk (to 1 in 115,000 and 1 in 26,000 for low- and high-variability, respectively), compared to additional product testing (to 1 in 21,000 and 1 in 11,000 for low- and high-variability, respectively). For low variability contamination, no highest-risk lots existed. Under high variability contamination, both interventions removed all highest-risk lots (about 0.05% of total). Yet, additional product testing rejected more lower-risk lots (about 1% of total), suggesting meaningful food waste tradeoffs. This model evaluates tradeoffs between interventions using industry-relevant risk metrics to support decision-making and can be adapted to assess other commodities, process stages, and less-studied interventions.

Microbiological hazards associated with the use of water in the post-harvest handling and processing operations of fresh and frozen fruits, vegetables and herbs (ffFVH). Part 2 - A dynamic mass balance model for handling and processing operations in ffFVH using water

A dynamic mass balance model was developed to simulate contamination dynamics in the process water of fresh and frozen fruits, vegetables and herbs (ffFVH) during processing and handling operations. The mass balance relates to the flux of water and product in a wash tank and the number of microbial cells released in the water, inactivated by the water disinfectant or transferred from the water back to the product. Critical variables describing microbial dynamics in water are: (i) the chemical oxygen demand (COD), as an indicator of the concentration of organic matter; (ii) free chlorine (FC) and particularly its antimicrobial fraction, hypochlorous acid (HOCl); and (iii) the microbial population levels. Model parameters include: (i) the dilution rate of the process water, representing the speed of system saturation, equal to the water flux divided by the tank volume; (ii) the transfer rates of total bacterial counts (TBC) and COD from product to water; and (iii) the specific inactivation rate of microorganisms due to HOCl. The protective effect of COD on microbial cells against FC is encompassed in the inactivation rate. HOCl is expressed as a function of temperature, pH and total chlorine. The model can simulate 'what if scenarios', based on user-defined process-specific and product/microorganism-specific parameters through a web R-based application. This model can help food business operators when selecting intervention strategies and conditions to maintain the microbiological quality of the process water or identify conditions that represent poor or proper water management practices. Testing alternative model structures and collecting data about operational conditions of handling and/or processing operations, microbial dynamics and the magnitude of the product-specific protective effect on microorganisms are recommended to improve the application of the model.

Microbiological hazards associated with the use of water in the post-harvest handling and processing operations of fresh and frozen fruits, vegetables and herbs (ffFVH). Part 4 (fresh-cut FVH process water management plan)

Water used in post-harvest handling and processing operations is an important risk factor for microbiological cross-contamination of fruits, vegetables and herbs (FVH). Industrial data indicated that the fresh-cut FVH sector is characterised by process water at cooled temperature, operational cycles between 1 and 15 h, and product volumes between 700 and 3000 kg. Intervention strategies were based on water disinfection treatments mostly using chlorine-based disinfectants. Water replenishment was not observed within studied industries. The industrial data, which included 19 scenarios were used to develop a guidance for a water management plan (WMP) for the fresh-cut FVH sector. A WMP aims to maintain the fit-for-purpose microbiological quality of the process water and consists of: (a) identification of microbial hazards and hazardous events linked to process water; (b) establishment of the relationship between microbiological and physico-chemical parameters; (c) description of preventive measures; (d) description of intervention measures, including their validation, operational monitoring and verification; and (e) record keeping and trend analysis. A predictive model was used to simulate water management outcomes, highlighting the need for water disinfection treatments to maintain the microbiological quality of the process water and the added value of water replenishment. Relying solely on water replenishment (at realistic feasible rates) does not avoid microbial accumulation in the water. Operational monitoring of the physico-chemical parameters ensures that the disinfection systems are operating effectively. Verification includes microbiological analysis of the process water linked to the operational monitoring outcomes of physico-chemical parameters. Although Escherichia coli and Listeria spp. could be indicators for assessing water quality, food business operators should set up and validate a tailored WMP to identify physico-chemical parameters, as well as microbial indicators and their threshold levels, as performance standards for maintaining the fit-for-purpose microbiological quality of the process water during post-harvest handling and processing operations.

Microbiological hazards associated with the use of water in the post-harvest handling and processing operations of fresh and frozen fruits, vegetables and herbs (ffFVH). Part 5 (Frozen FVH process water management plan)

Water used in post-harvest handling and processing operations is an important risk factor for microbiological cross-contamination of fruits, vegetables and herbs (FVH). Industrial data indicated that the frozen FVH sector is characterised by operational cycles between 8 and 120 h, variable product volumes and no control of the temperature of process water. Intervention strategies were limited to the use of water disinfection treatments such as peroxyacetic acid and hydrogen peroxide. Chlorine-based disinfectants were not used, and water replenishment was not observed within studied industries. The industrial data, which included 13 scenarios, were used to develop a guidance for a water management plan (WMP) for the frozen FVH sector. A WMP aims to maintain the fit-for-purpose microbiological quality of the process water and consists of: (a) identification of microbial hazards and hazardous events linked to process water; (b) establishment of the relationship between microbiological and physico-chemical parameters; (c) description of preventive measures; (d) description of intervention measures, including their validation, operational monitoring and verification; and (e) record keeping and trend analysis. A predictive model was used to simulate water management outcomes, highlighting the need for water disinfection treatments to maintain the microbiological quality of the process water and the added value of water replenishment. Relying solely on water replenishment (at realistic feasible rates) does not avoid microbial accumulation in the water. Operational monitoring of the physico-chemical parameters ensures that the disinfection systems are operating effectively. Verification includes microbiological analysis of the process water linked to the operational monitoring outcomes of physico-chemical parameters. Food business operators should set up and validate a tailored WMP to identify physico-chemical parameters, as well as microbial indicators and their threshold levels as performance standards for maintaining the fit-for-purpose microbiological quality of the process water during post-harvest handling and processing operations.

Microbiological hazards associated with the use of water in the post-harvest handling and processing operations of fresh and frozen fruits, vegetables and herbs (ffFVH). Part 3 (Fresh-whole FVH process water management plan)

Water used in post-harvest handling and processing operations is an important risk factor for microbiological cross-contamination of fruits, vegetables and herbs (FVH). Industrial data indicated that the fresh-whole FVH sector is characterised by very variable operational cycle duration (between 8 and 900 h), large product volumes (e.g. more than 6000 tonnes) and process water at 2.8-25.0°C. Intervention strategies were based on water disinfection treatments, mostly using chlorine-based disinfectants. Water replenishment was not observed within studied industries. The industrial data, which included 29 scenarios were used to develop a guidance for a water management plan (WMP) for the fresh-whole FVH sector. A WMP aims to maintain the fit-for-purpose microbiological quality of the process water and consists of (a) identification of microbial hazards and hazardous events linked to process water; (b) establishment of the relationship between microbiological and physico-chemical parameters; (c) description of preventive measures; (d) description of intervention measures, including their validation, operational monitoring and verification; and (e) record keeping and trend analysis. A predictive model was used to simulate water management outcomes, highlighting the need for water disinfection treatments to maintain the microbiological quality of the process water and the added value of water replenishment. Relying solely on water replenishment (at realistic feasible rates) does not avoid microbial accumulation in the water. Operational monitoring of the physico-chemical parameters ensures that the disinfection systems are operating effectively. Verification includes microbiological analysis of the process water linked to the operational monitoring outcomes of physico-chemical parameters. Food business operators (FBOps) should set up and validate a tailored WMP to identify physico-chemical parameters, as well as microbial indicators and their threshold levels, as performance standards for maintaining the fit-for-purpose microbiological quality of the process water during post-harvest handling and processing operations.

Biofilm formation by Listeria monocytogenes from the meat processing industry environment and the use of different combinations of detergents, sanitizers, and UV-A radiation to control this microorganism in planktonic and sessile forms

This study aimed to evaluate the ability of biofilm formation by L. monocytogenes from the meat processing industry environment, as well as the use of different combinations of detergents, sanitizers, and UV-A radiation in the control of this microorganism in the planktonic and sessile forms. Four L. monocytogenes isolates were evaluated and showed moderate ability to form biofilm, as well as carried genes related to biofilm production (agrB, agrD, prfA, actA, cheA, cheY, flaA, sigB), and genes related to tolerance to sanitizers (lde and qacH). The biofilm-forming isolates of L. monocytogenes were susceptible to quaternary ammonium compound (QAC) and peracetic acid (PA) in planktonic form, with minimum inhibitory concentrations of 125 and 75 ppm, respectively, for contact times of 10 and 5 min. These concentrations are lower than those recommended by the manufacturers, which are at least 200 and 300 ppm for QAC and PA, respectively. Biofilms of L. monocytogenes formed from a pool of isolates on stainless steel and polyurethane coupons were subjected to 14 treatments involving acid and enzymatic detergents, QAC and PA sanitizers, and UV-A radiation at varying concentrations and contact times. All treatments reduced L. monocytogenes counts in the biofilm, indicating that the tested detergents, sanitizers, and UV-A radiation exhibited antimicrobial activity against biofilms on both surface types. Notably, the biofilm formed on polyurethane showed greater tolerance to the evaluated compounds than the biofilm on stainless steel, likely due to the material's surface facilitating faster microbial colonization and the development of a more complex structure, as observed by scanning electron microscopy. Listeria monocytogenes isolates from the meat processing industry carry genes associated with biofilm production and can form biofilms on both stainless steel and polyurethane surfaces, which may contribute to their persistence within meat processing lines. Despite carrying sanitizer tolerance genes, QAC and PA effectively controlled these microorganisms in their planktonic form. However, combinations of detergent (AC and ENZ) with sanitizers (QAC and PA) at minimum concentrations of 125 ppm and 300 ppm, respectively, were the most effective.

Lettuce Genotype-Dependent Effects of Temperature on Escherichia coli O157:H7 Persistence and Plant Head Growth

Lettuce has been commonly associated with the contamination of human pathogens, such as Escherichia coli O157:H7 (hereafter O157:H7), which has resulted in serious foodborne illnesses. Contamination events may happen throughout the farm-to-fork chain, when O157:H7 colonizes edible tissues and closely interacts with the plant. Environmental conditions have a significant impact on many plant-microbe interactions; however, it is currently unknown whether temperature affects O157:H7 colonization of the lettuce phyllosphere. In this study, we investigated the relationship between elevated growth temperatures, O157:H7 persistence, and lettuce head growth using 25 lettuce genotypes. Plants were grown under optimal or elevated temperatures for 3.5 weeks before being inoculated with O157:H7. The bacterial population size in the phyllosphere and lettuce head area was estimated at 0- and 10-days postinoculation (DPI) to assess bacterial persistence and head growth during contamination. We found that growing temperature can have a positive, negative, or no effect on O157:H7 persistence depending on the lettuce genotype. Furthermore, temperature had a greater effect on head area size than the presence of O157:H7. The results suggested that the combination of plant genotype and temperature level is an important factor for O157:H7 colonization of lettuce and the possibility to combine desirable food safety traits with heat tolerance into the lettuce germplasm.

Multimode ultrasonic-assisted decontamination of fruits and vegetables: A review

Fruits and vegetables (F&V) are a significant part of our diet consumption. Microbial and pesticide residues are the predominant safety hazards of F&V consumption. Ordinary water washing has a very limited effect on removing microorganisms and pesticide residues and requires high water usage. Ultrasound, as an environmentally friendly technology, shows excellent potential for reducing microbial contamination and pesticide residue. This paper summarizes the research on ultrasound application in F&V washing, including the removal of microbial and pesticide residues and the comprehensive effect on their physicochemical characteristics. Furthermore, multimode ultrasonic-assisted techniques like multi-frequency and sequential ultrasound, combined with novel and conventional methods, can enhance the ultrasound-based effect and be more effective and sustainable in preventing F&V from microbial contamination. Overall, this work explicitly establishes the background on the potential for ultrasound cleaning and disinfection in the food industry as a green, effective, and ultimate method of preventing foodborne illnesses.

Berry Pomace Extracts as a Natural Washing Aid to Mitigate Enterohaemorrhagic E. coli in Fresh Produce

Enterohemorrhagic Escherichia coli (EHEC) outbreaks have been frequently linked to the consumption of produce. Furthermore, produce grown on organic farms possess a higher risk, as the farmers avoid antibiotics and chemicals. This study sets out to evaluate the effectiveness of advanced postharvest disinfection processes using berry pomace extracts (BPEs) in reducing EHEC load in two common leafy greens, spinach and lettuce. Spinach and lettuce were inoculated with ~5 log CFU/leaf EHEC EDL-933 and then treated with three different concentrations of BPE (1, 1.5, and 2 gallic acid equivalent, GAE mg/mL) for increasing periods of time. After the wash, the bacteria were quantified. Changes in the relative expression of virulence genes and the genes involved in cell division and replication and response against stress/antibiotics were studied. We observed a significant reduction in EHEC EDL933, ranging from 0.5 to 1.6 log CFU/spinach leaf (p < 0.05) washed with BPE water. A similar trend of reduction, ranging from 0.3 to 1.3 log CFU/mL, was observed in pre-inoculated lettuce washed with BPE water. We also quantified the remaining bacterial population in the residual treatment solutions and found the survived bacterial cells (~3 log CFU/mL) were low despite repeated washing with the same solution. In addition, we evaluated the phenolic concentration in leftover BPE, which did not change significantly, even after multiple uses. Alterations in gene expression levels were observed, with downregulation ranging from 1 to 3 log folds in the genes responsible for the adhesion and virulence of EHEC EDL933 and significant upregulation of genes responsible for survival against stress. All other genes were upregulated, ranging from 2 to 7 log folds, with a dose-dependent decrease in expression. This finding shows the potential of BPE to be used for sanitation of fresh produce as a natural and sustainable approach.

Using ultrasonic washing combined with UV-LEDs as a novel chemical-free method to disinfect fresh ready-to-eat produce

The consumption of ready-to-eat fresh produce raises the issue of food-borne pathogen infections; thus, disinfecting ready-to-eat produce for commercial use, such as in homes and restaurants, is important to ensure food safety. Chemical sanitizers are typically used for disinfection. Ultraviolet-light emitting diodes (UV-LEDs) are a novel non-thermal disinfection technology that consumes less energy and generates less heat than traditional UV lamps, making them more appealing to consumers. In this study, we combined ultrasonic (US) washing method with UV-LEDs (US-UV-LEDs) to develop a technique for disinfecting fresh produce without using chemical sanitizers and compared its efficacy with three common household sanitizers ("84" (sodium hypochlorite) disinfectant, kettle descaler (citric acid), and vinegar (acetic acid)). In addition, we investigated the efficacy of this method in controlling pathogen numbers in the water used to wash (washing water) the produce to prevent cross-contamination between water and produce. Cherry tomatoes and lettuce were selected as produce models and Salmonella Typhimurium and Escherichia coli O157:H7 were used as the bacterial models. The results showed that US-UV-LEDs reduced the numbers of S. Typhimurium and E. coli O157:H7 on produce by 2.1-2.2 log CFU/g, consistent with the results achieved by the three household sanitizers; however, kettle descaler and vinegar had a limited effect (2.6-3.5 log CFU/mL) on residual pathogens in the washing water. Furthermore, we created washing water with low (754 mg/L) and high (1425 mg/L) chemical oxygen demand (COD) levels and determined the disinfection efficacy of "84" disinfectant and US-UV-LEDs. The results showed that US-UV-LEDs reduced the number of S. Typhimurium and E. coli O157:H7 by 2.0-2.1 and 1.8-2.1 log CFU/g under low and high COD levels, respectively, which was similar a result to that of "84" disinfectant. However, the residual pathogen numbers in the washing water were reduced to 1.4-1.9 log CFU/mL after treatment with US-UV-LED under high COD, whereas the pathogens were undetected in the washing water disinfected with "84" disinfectant. These results suggest that US-UV-LEDs have better application potential than acidic household sanitizers, but chlorine sanitizer remains the most effective disinfecting method.

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.

Exploring the Antimicrobial Efficacy of Low-Cost Commercial Disinfectants Utilized in the Agro-Food Industry Wash Tanks: Towards Enhanced Hygiene Practices

The increase in vegetable consumption has underlined the importance of minimizing the risks associated with microbiological contamination of fresh produce. The critical stage of the vegetable washing process has proven to be a key point for cross-contamination and the persistence of pathogens. In this context, the agri-food industry has widely adopted the use of disinfectants to reduce the bacterial load in the wash water. Therefore, we conducted laboratory-scale experiments in order to demonstrate the antimicrobial activity of disinfectants used in the wash tank of agro-food industries. Different wash water matrices of shredded lettuce, shredded cabbage, diced onion, and baby spinach were treated with sodium hypochlorite (NaClO), chlorine dioxide (ClO2), and per-oxyacetic acid (PAA) at recommended concentrations. To simulate the presence of pathogenic bacteria, a cocktail of E. coli O157:H7 was inoculated into the process water samples (PWW) to determine whether concentrations of disinfectants inhibit the pathogen or bring it to a viable non-culturable state (VBNC). Hereby, we used quantitative qPCR combined with different photo-reactive dyes such as ethidium monoazide (EMA) and propidium monoazide (PMA). The results indicated that concentrations superior to 20 ppm NaClO inhibit the pathogen E. coli O157:H7 artificially inoculated in the process water. Concentrations between 10-20 ppm ClO2 fail to induce the pathogen to the VBNC state. At concentrations of 80 ppm PAA, levels of culturable bacteria and VBNC of E. coli O157:H7 were detected in all PWWs regardless of the matrix. Subsequently, this indicates that the recommended concentrations of ClO2 and PAA for use in the fresh produce industry wash tank do not inhibit the levels of E. coli O157:H7 present in the wash water.

The Use of Ultraviolet Irradiation to Improve the Efficacy of Acids That Are Generally Recognized as Safe for Disinfecting Fresh Produce in the Ready-to-Eat Stage

Fresh-cut produce is usually produced under standardized disinfection processes, which are unavailable at the ready-to-eat stage. Currently, chemical sanitizers are used for washing, but their disinfection efficacy is limited. In this study, UV-C (1.03 kJ/m2) was combined with organic acids that are generally recognized as safe (GRAS), including citric, malic, acetic, and lactic acids (LAs), to wash lettuce and cherry tomatoes that are contaminated with Escherichia coli O157:H7 and Salmonella Typhimurium. The results showed that LA was the most effective treatment among the single treatments, with a pathogen reduction and cross-contamination incidence of 2.0-2.3 log CFU/g and 28-35%, respectively. After combining with UV-C, the disinfection efficacy and cross-contamination prevention capacity of the four GRAS acids significantly improved. Among the combination treatments, the highest pathogen reduction (2.5-2.7 log CFU/g) and the lowest cross-contamination incidence (11-15%) were achieved by LA-UV. The analyses of ascorbic acid, chlorophyll, lycopene, antioxidant capacity, and ΔE indicated that neither the single nor combination treatments negatively affected the quality properties. These results provide a potential hurdle technology for fresh produce safety improvement at the ready-to-eat stage.

Evaluating the efficacy of peroxyacetic acid in preventing Salmonella cross-contamination on tomatoes in a model flume system

The use of flume tanks for tomato processing has been identified as a potential source of cross-contamination, which could result in foodborne illness. This study's objective was to assess the efficacy of peroxyacetic acid (PAA) at a concentration of ≤80 mg/L in preventing Salmonella enterica cross-contamination under various organic loads in a benchtop model tomato flume tank. The stability of 80 mg/L PAA at different chemical oxygen demand (COD) levels was also tested. Tomatoes were spot inoculated with a five-serovar rifampin-resistant (rif+) Salmonella cocktail (106 or 108 colony forming unit (CFU)/tomato). Inoculated (n = 3) and uninoculated (n = 9) tomatoes were introduced into the flume system containing 0-80 mg/L PAA and 0 or 300 mg/L COD. After washing for 30, 60, or 120 s, uninoculated tomatoes were sampled and analyzed for cross-contamination. All experiments were conducted in triplicate. Increasing the organic load (measured as COD) affected the stability of PAA in water with significantly faster dissociation when exposed to 300 mg/L COD. The concentration of PAA, inoculum level, COD levels, and time intervals were all significant factors that affected cross-contamination. Cross-contamination occurred at the high inoculum level (108 CFU/tomato) even when 80 mg/L PAA was present in the model flume tank, regardless of the organic load level. When the tomatoes were contaminated at a level of 106 CFU/tomato, concentrations as low as 5 mg/L of PAA were effective in preventing cross-contamination at 0 mg/L COD; however, 100 % tomatoes (9/9) were positive when the organic load increased to 300 mg/L COD. When the PAA concentration was increased to 10 mg/L, it effectively prevented cross-contamination in the tank, regardless of the presence of organic load. These results suggest that using PAA at concentrations below the maximum limit remains effective in limiting bacterial cross-contamination and offers a more environment-friendly option for tomato packinghouse operators.

Low-frequency transmission and persistence of antimicrobial-resistant bacteria and genes from livestock to agricultural soil and crops through compost application

Livestock excrement is composted and applied to agricultural soils. If composts contain antimicrobial-resistant bacteria (ARB), they may spread to the soil and contaminate cultivated crops. Therefore, we investigated the degree of transmission of ARB and related antimicrobial resistance genes (ARGs) and, as well as clonal transmission of ARB from livestock to soil and crops through composting. This study was conducted at Rakuno Gakuen University farm in Hokkaido, Japan. Samples of cattle feces, solid and liquid composts, agricultural soil, and crops were collected. The abundance of Escherichia coli, coliforms, β-lactam-resistant E. coli, and β-lactam-resistant coliforms, as well as the copy numbers of ARG (specifically the bla gene related to β-lactam-resistant bacteria), were assessed using qPCR through colony counts on CHROMagar ECC with or without ampicillin, respectively, 160 days after compost application. After the application of the compost to the soil, there was an initial increase in E. coli and coliform numbers, followed by a subsequent decrease over time. This trend was also observed in the copy numbers of the bla gene. In the soil, 5.0 CFU g-1 E. coli was detected on day 0 (the day post-compost application), and then, E. coli was not quantified on 60 days post-application. Through phylogenetic analysis involving single nucleotide polymorphisms (SNPs) and using whole-genome sequencing, it was discovered that clonal blaCTX-M-positive E. coli and blaTEM-positive Escherichia fergusonii were present in cattle feces, liquid compost, and soil on day 0 as well as 7 days post-application. This showed that livestock-derived ARB were transmitted from compost to soil and persisted for at least 7 days in soil. These findings indicate a potential low-level transmission of livestock-associated bacteria to agricultural soil through composts was observed at low frequency, dissemination was detected. Therefore, decreasing ARB abundance during composting is important for public health.

Evaluation of Enterococcus faecium NRRL B-2354 as a surrogate for Listeria monocytogenes during chlorine and peroxyacetic acid interventions in simulated apple dump tank water

Sanitizers are widely incorporated in commercial apple dump tank systems to mitigate the cross-contamination of foodborne pathogens. This study validated the suitability of Enterococcus faecium NRRL B-2354 as a surrogate for Listeria monocytogenes during sanitizer interventions in dump tank water systems. E. faecium NRRL B-2354 inoculated on apples exhibited statistically equivalent susceptibility to L. monocytogenes when exposed to chlorine-based sanitizers (25-100 ppm free chlorine (FC)) and peroxyacetic acid (PAA, 20-80 ppm) in simulated dump tank water (SDTW) with 1000 ppm chemical oxygen demand (COD), resulting in 0.2-0.9 and 1.1-1.7 log CFU/apple reduction, respectively. Increasing the contact time did not affect sanitizer efficacies against E. faecium NRRL B-2354 and L. monocytogenes on apples. Chlorine and PAA interventions demonstrated statistically similar efficacies against both bacteria inoculated in SDTW. Chlorine at 25 and 100 ppm FC for 0.5-5 min contact yielded ~37.68-78.25 % and > 99.85 % inactivation, respectively, in water with 1000-4000 ppm COD, while ~51.55-99.86 % and > 99.97 % inactivation was observed for PAA at 20 and 80 ppm, respectively. No statistically significant difference was observed between the transference of E. faecium NRRL B-2354 and L. monocytogenes from inoculated apples to uninoculated apples and water, and from water to uninoculated apples during chlorine- or PAA-treated SDTW exposure. The data suggest E. faecium NRRL B-2354 is a viable surrogate for L. monocytogenes in dump tank washing systems, which could be used to predict the anti-Listeria efficacy of chlorine and PAA interventions during commercial apple processing. Further investigations are recommended to assess the suitability of E. faecium NRRL B-2354 as a surrogate for L. monocytogenes, when using different sanitizers and different types of produce to ensure reliable and comprehensive results.

Human intestinal enteroids and predictive models validate the operational limits of sanitizers used for viral disinfection of vegetable process wash water

Vegetables are globally associated with a considerable number of foodborne outbreaks caused by viral infections, specifically human norovirus. In fresh produce industry, washing represents a critical step for food safety as process wash water (PWW) needs to be maintained at appropriate microbial quality to prevent water-mediated cross-contamination. This study aimed to explore the disinfection efficacy of chlorine (free chlorine, FC), chlorine dioxide (ClO2) and peracetic acid (PAA) in PWW against infectious human norovirus and Tulane virus (TV). First, we tested the extent of TV inactivation in baby leaf, bell pepper, and vegetables mix PWW and monitored the viral decay by cell culture. Then, inactivation kinetics were defined for infectious human norovirus exposed to FC, ClO2 and PAA in baby leaves PWW using the human intestinal enteroids (HIE) system. Finally, kinetic inactivation models were fitted to TV reduction and decay of sanitizers to aid the implementation of disinfection strategies. Results showed that >8 log10 human norovirus and 3.9 log10 TV were inactivated by 20 ppm FC within 1 min; and by 3 ppm ClO2 in 1 min (TV) or 5 min (norovirus). PAA treatment at 80 ppm reduced ca. 2 log10 TV but not completely inactivated the virus even after 20 min exposure, while 5 min treatment prevented norovirus replication in HIE. TV inactivation in PWWs was described using an exponential decay model. Taking these data together, we demonstrated the value of applying the HIE model to validate current operational limits for the most commonly used sanitizers. The inactivation kinetics for human norovirus and TV, along with the predictive model described in this study expand the current knowledge to implement post-harvest produce safety procedures in industry settings.

Disinfection efficiency of chlorine dioxide and peracetic acid against MNV-1 and HAV in simulated soil-rich wash water

Wash water from fresh vegetables and root vegetables is an important vehicle for foodborne virus transmission. However, there is lack of assessing rapid viral inactivation strategies in wash water characterized by a high soil content at the post-harvest stage. Considering the significance of food safety during the washing stage for fresh and root vegetable produce prior to marketing, we assessed the inactivation efficacy by using chlorine dioxide (ClO2) and peracetic acid (PAA) against a surrogate of human norovirus (murine norovirus 1, MNV-1) and hepatitis A virus (HAV), in wash water containing black soil and clay loam. The results indicated that MNV-1 and HAV were reduced to the process limit of detection (PLOD), with reductions ranging from 4.89 to 6.35 log10 PFU, and 4.63 to 4.96 log10 PFU when treated with ClO2 at 2.5 ppm for 10 mins. Comparatively, when treated with 500 ppm of PAA for 10 mins, MNV-1 and HAV were maximum reduced to 1.75 ± 0.23 log10 PFU (4.50 log10 PFU reduction) and 2.13 ± 0.12 log10 PFU (2.72 log10 PFU reduction). This demonstrated the efficacy of ClO2 in eliminating foodborne viruses in soil-rich wash water. When we validated the recovery of the virus from two types of wash water, the pH (9.24 ± 0.33 and 5.95 ± 0.05) had no impact on the recovery of MNV-1, while the recovery of HAV was less than 1 %. By adjusting the pH to a neutral level, recovery of HAV and its RNA levels was increased to 15.94 and 3.89 %. Thus, this study emphasized the critical role of pH in the recovery of HAV from the complex soil-rich aqueous environment, and the efficacy of ClO2 serving as a pivotal reference for the development of control strategies against foodborne viruses in the supply chain of fresh and root vegetables.

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.

Transfer of Enterococcus faecium and Salmonella enterica during simulated postharvest handling of yellow onions (Allium cepa)

Bacterial transfer during postharvest handling of fresh produce provides a mechanism for spreading pathogens, but risk factors in dry environments are poorly understood. The aim of the study was to investigate factors influencing bacterial transfer between yellow onions (Allium cepa) and polyurethane (PU) or stainless steel (SS) under dry conditions. Rifampin-resistant Enterococcus faecium NRRL B-2354 or a five-strain cocktail of Salmonella was inoculated onto onion skin or PU surfaces at high or moderate levels using peptone, onion extract, or soil water as inoculum carriers. Transfer from inoculated to uninoculated surfaces was conducted using a texture analyzer to control force, time, and number of contacts. Transfer rates (ratio of recipient surface to donor surface populations) of E. faecium (4-5%) were significantly higher than those of Salmonella (0.5-0.6%) at the high (7 log CFU/cm2) but not moderate (5 log CFU/cm2) inoculum levels. Significantly higher populations of E. faecium transferred from onion to PU than from PU to onion. The transfer rates of E. faecium were impacted by inoculum carrier (61% [onion extract], 1.6% [peptone], and 0.31% [soil]) but not by inoculation level or recipient surface (PU versus SS). Bacterial transfer during dry onion handling is significantly dependent on bacterial species, inoculation levels, inoculum carrier, and transfer direction.

An Effective Sanitizer for Fresh Produce Production: In Situ Plasma-Activated Water Treatment Inactivates Pathogenic Bacteria and Maintains the Quality of Cucurbit Fruit

The effect of plasma-activated water (PAW) generated with a dielectric barrier discharge diffusor (DBDD) system on microbial load and organoleptic quality of cucamelons was investigated and compared to the established sanitizer, sodium hypochlorite (NaOCl). Pathogenic serotypes of Escherichia coli, Salmonella enterica, and Listeria monocytogenes were inoculated onto the surface of cucamelons (6.5 log CFU g-1) and into the wash water (6 log CFU mL-1). PAW treatment involved 2 min in situ with water activated at 1,500 Hz and 120 V and air as the feed gas; NaOCl treatment was a wash with 100 ppm total chlorine; control treatment was a wash with tap water. PAW treatment produced a 3-log CFU g-1 reduction of pathogens on the cucamelon surface without negatively impacting quality or shelf life. NaOCl treatment reduced the pathogenic bacteria on the cucamelon surface by 3 to 4 log CFU g-1; however, this treatment also reduced fruit shelf life and quality. Both systems reduced 6-log CFU mL-1 pathogens in the wash water to below detectable limits. The critical role of superoxide anion radical (·O2-) in the antimicrobial power of DBDD-PAW was demonstrated through a Tiron scavenger assay, and chemistry modeling confirmed that ·O2- generation readily occurs in DBDD-PAW generated with the employed settings. Modeling of the physical forces produced during plasma treatment showed that bacteria likely experience strong local electric fields and polarization. We hypothesize that these physical effects synergize with reactive chemical species to produce the acute antimicrobial activity seen with the in situ PAW system. IMPORTANCE Plasma-activated water (PAW) is an emerging sanitizer in the fresh food industry, where food safety must be achieved without a thermal kill step. Here, we demonstrate PAW generated in situ to be a competitive sanitizer technology, providing a significant reduction of pathogenic and spoilage microorganisms while maintaining the quality and shelf life of the produce item. Our experimental results are supported by modeling of the plasma chemistry and applied physical forces, which show that the system can generate highly reactive ·O2- and strong electric fields that combine to produce potent antimicrobial power. In situ PAW has promise in industrial applications as it requires only low power (12 W), tap water, and air. Moreover, it does not produce toxic by-products or hazardous effluent waste, making it a sustainable solution for fresh food safety.

The Effect of Water Hardness and pH on the Efficacy of Peracetic Acid and Sodium Hypochlorite against SARS-CoV-2 on Food-Contact Surfaces

Sodium hypochlorite (NaOCl) and peracetic acid (PAA) are commonly used disinfectants with a maximum recommended concentration of 200 ppm for food-contact surfaces. The objectives of this study were to assess the effect of pH and water hardness on NaOCl and PAA efficacy against SARS-CoV-2 on stainless steel (SS). The two disinfectants were prepared at 200 ppm in water of hardness 150 or 300 ppm with the final pH adjusted to 5, 6, 7, or 8. Disinfectants were applied to virus-contaminated SS for one minute at room temperature following the ASTM E2197 standard assay. SARS-CoV-2 infectivity was quantified using TCID50 assay on Vero-E6 cells. In general, increasingly hard water decreased the efficacy of NaOCl while increasing the efficacy of PAA. Hard water at 300 ppm significantly increased virus log reduction with PAA at pH 8 by ~1.5 log. The maximum virus log reductions were observed at pH 5 for both NaOCl (~1.2 log) and PAA (~2 log) at 150 and 300 ppm hard water, respectively. In conclusion, PAA performed significantly better than NaOCl with harder water. However, both disinfectants at 200 ppm and one minute were not effective (≤3 log) against SARS-CoV-2 on contaminated food-contact surfaces, which may facilitate the role of these surfaces in virus transmission.

Chlorate Levels in Dairy Products Produced and Consumed in Ireland

In recent years, chlorate has become a residue of concern internationally, due to the risk that it poses to thyroid gland function. However, little is known about its occurrence in dairy products of Irish origin. To address this, a study was conducted in which samples of milk (n = 317), cream (n = 199), butter (n = 178), cheese (n = 144) and yoghurt (n = 440) were collected from grocery stores in the Republic of Ireland. Sampling was conducted across spring, summer, autumn and winter of 2021. Samples from multiple manufacturers of each respective dairy product were procured and analysed for chlorate using UPLC-MS/MS. Chlorate was detected in milk, cream, natural, blueberry, strawberry and raspberry yoghurts. Mean chlorate levels detected in these products were 0.0088, 0.0057, 0.055, 0.067, 0.077 and 0.095 mg kg^-1, respectively. Chlorate was undetected in butter and cheese (<0.01 mg kg^-1). All products sampled, except yoghurt, were found to be compliant with the EU limit for chlorate in milk (0.10 mg kg^-1). Some manufacturers produced product with greater incidence and levels of chlorate. Chlorate levels from samples tested at different times of the year did not differ significantly, with the exception of strawberry and raspberry yoghurts which had higher chlorate levels in the winter period.

Effect of Food Matrix and Treatment Time on the Effectiveness of Grape Seed Extract as an Antilisterial Treatment in Fresh Produce

Listeriosis outbreaks were associated with contaminated fruits and vegetables, including cantaloupe, apples, and celery. Grape seed extract (GSE) is a natural antimicrobial with potential for reducing Listeria monocytogenes contamination in food. This study assessed the effectiveness of GSE to reduce L. monocytogenes on fresh produce and the impact of food matrices on its antilisterial activity. GSE showed MIC values of 30-35 μg/mL against four Listeria strains used in this study. A total of 100 g portions of cantaloupe, apples, and celery were inoculated with L. monocytogenes and treated with 100-1000 μg/mL of GSE for 5 or 15 min. Results were analyzed using Rstudio and a Tukey's test. Treated produce had significantly lower L. monocytogenes counts than the control samples (p-value < 0.05). The inhibition was significantly higher on apples and lowest on cantaloupe. Moreover, a 15 min treatment was found to be more effective than a 5 min treatment in reducing L. monocytogenes on all produce types. The reduction in L. monocytogenes levels varied between 0.61 and 2.5 log₁₀ CFU reduction, depending on the treatment concentration, duration, and produce matrix. These findings suggest that GSE is an effective antilisterial treatment for fresh produce, with varying levels of effectiveness depending on the food matrix and treatment time.

Pre-harvest biocontrol of Listeria and Escherichia coli O157 on lettuce and spinach by lactic acid bacteria

Recent outbreaks linked to contaminated leafy greens underline the need for identifying effective natural approaches to improve produce safety at pre-harvest level. Lactic acid bacteria (LAB) have been evaluated as biocontrol agents in food products. In this study, the efficacy of a cocktail of LAB including Lactococcus lactis, Lactiplantibacillus plantarum, Lactobacillus johnsonii, and Lactobacillus acidophilus as pre-harvest biocontrol agents against Listeria and Escherichia coli O157 on lettuce and spinach was investigated. Bacterial pathogens L. monocytogenes and E. coli O157:H7 and the non-pathogenic surrogates L. innocua and E. coli O157:H12 were used to spray-inoculate cultivars of lettuce and spinach grown in growth chamber and in field, respectively. Inoculated plants were spray-treated with water or a cocktail of LAB. On day 0, 3, and 5 post-inoculation, four samples from each group were collected and bacterial populations were determined by serial dilution and spiral plating on selective agars. LAB treatment exhibited an immediate antimicrobial efficacy against L. monocytogenes and E. coli O157:H7 on "Green Star" lettuce by ~2 and ~ 1 log reductions under growth chamber conditions, respectively (P < 0.05). The effect of LAB against E. coli O157:H7 on "New Red Fire" lettuce remained effective during the 5-day period in growth chamber (P < 0.05). Treatment of LAB delivered an effective bactericidal effect against E. coli O157:H12 immediately after application on the field-grown lettuce plants (P < 0.05). Approximately 1 log L. innocua reduction was observed on "Matador" and "Palco" spinach on day 5 (P < 0.05). Results of this study support that LAB could potentially be applied as biocontrol agents for controlling Listeria and E. coli O157 contamination on leafy greens at the pre-harvest level.

Cross-contamination of Escherichia coli O157:H7 and Listeria monocytogenes in the viable but non-culturable (VBNC) state during washing of leafy greens and the revival during shelf-life

Some water disinfection treatments, such as chlorine and chlorine dioxide, used in the fresh-cut industry to maintain the microbiological quality of process water (PW), inactivate bacterial cells in the water but they also lead to the induction of an intermediate state between viable and non-viable known as viable but non-culturable (VBNC) state. Viable cells can participate in cross-contamination events but the significance of VBNC cells in PW, transfer to the product and potential resuscitation capacity during storage is unclear. The present study aims to determine first, if VBNC cells present in PW can cross-contaminate leafy greens during washing and secondly its potential revival during shelf-life. Process water characterized by a high chemical oxygen demand, due to the presence of high levels of organic matter, was inoculated with Listeria monocytogenes or Escherichia coli O157:H7. Inoculated PW was then treated for 1 min with chlorine dioxide (3 mg/L) or chlorine (5 mg/L) to generate VBNC cells. Absence of culturable cells was confirmed by plate count and VBNC cells by viability quantitative polymerase chain reaction (v-qPCR) complemented with two dyes, ethidium (EMA) and propidium (PMAxx) monoazide. Cross-contamination of shredded lettuce was demonstrated by monitoring the VBNC cells after washing the product for 1 min in the contaminated PW and during shelf life (15 days at 7 °C). In the case of L. monocytogenes, considering the total concentration of L. monocytogenes VBNC cells present in the PW, only a low proportion of cells were able to cross-contaminate the product during washing. VBNC L. monocytogenes cells were able to resuscitate on the product during shelf life, although levels of cultivable bacteria, close to the limit if detection (0.7 ± 0.0 log CFU/g), were only detected at the end of storage. On the other hand, VBNC cells of E. coli O157:H7 present in PW were not able to cross-contaminate shredded lettuce during washing. Moreover, when shredded lettuce was artificially inoculated with VBNC E. coli O157:H7, resuscitation of the VBNC cells during storage (15 days at 7 °C) was not observed. Based on the results obtained, injured L. monocytogenes cells present in the PW are able to be transferred to the product during washing. If VBNC L. monocytogenes cells present in leafy greens (shredded lettuce and baby spinach), they can resuscitate, although cultivable numbers remained very low. Taking all the results together, it could be concluded that under industrial conditions, VBNC cells can be transferred from water to product during washing, but their capacity to resuscitate in the leafy greens during storage is low.

Leveraging risk assessment for foodborne outbreak investigations: The Quantitative Risk Assessment-Epidemic Curve Prediction Model

Root cause analysis can be used in foodborne illness outbreak investigations to determine the underlying causes of an outbreak and to help identify actions that could be taken to prevent future outbreaks. We developed a new tool, the Quantitative Risk Assessment-Epidemic Curve Prediction Model (QRA-EC), to assist with these goals and applied it to a case study to investigate and illustrate the utility of leveraging quantitative risk assessment to provide unique insights for foodborne illness outbreak root cause analysis. We used a 2019 Salmonella outbreak linked to melons as a case study to demonstrate the utility of this model (Centers for Disease Control and Prevention [CDC], 2019). The model was used to evaluate the impact of various root cause hypotheses (representing different contamination sources and food safety system failures in the melon supply chain) on the predicted number and timeline of illnesses. The predicted number of illnesses varied by contamination source and was strongly impacted by the prevalence and level of Salmonella contamination on the surface/inside of whole melons and inside contamination niches on equipment surfaces. The timeline of illnesses was most strongly impacted by equipment sanitation efficacy for contamination niches. Evaluations of a wide range of scenarios representing various potential root causes enabled us to identify which hypotheses, were likely to result in an outbreak of similar size and illness timeline to the 2019 Salmonella melon outbreak. The QRA-EC framework can be adapted to accommodate any food-pathogen pairs to provide insights for foodborne outbreak investigations.

Electrolyzed-Reduced Water: Review II: Safety Concerns and Effectiveness as a Source of Hydrogen Water

Many studies demonstrate the safety of alkaline-electrolyzed-reduced water (ERW); however, several animal studies have reported significant tissue damage and hyperkalemia after drinking ERW. The mechanism responsible for these results remains unknown but may be due to electrode degradation associated with the production of higher pH, in which platinum nanoparticles and other metals that have harmful effects may leach into the water. Clinical studies have reported that, when ERW exceeds pH 9.8, some people develop dangerous hyperkalemia. Accordingly, regulations on ERW mandate that the pH of ERW should not exceed 9.8. It is recommended that those with impaired kidney function refrain from using ERW without medical supervision. Other potential safety concerns include impaired growth, reduced mineral, vitamin, and nutrient absorption, harmful bacterial overgrowth, and damage to the mucosal lining causing excessive thirst. Since the concentration of H2 in ERW may be well below therapeutic levels, users are encouraged to frequently measure the H2 concentration with accurate methods, avoiding ORP or ORP-based H2 meters. Importantly, although, there have been many people that have used high-pH ERW without any issues, additional safety research on ERW is warranted, and ERW users should follow recommendations to not ingest ERW above 9.8 pH.

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

Effect of ultraviolet light treatment on microbiological safety and quality of fresh produce: An overview

Fresh and fresh-cut fruits and vegetables have been associated in several foodborne illness outbreaks. Although investigations from those outbreaks reported that the contamination with pathogenic microorganisms may occur at any point in the farm to fork continuum, effective control strategies are still being widely investigated. In that direction, the concept of hurdle technology involving a sequence of different interventions have been widely explored. Among those interventions, ultraviolet (UV) light alone or in combination with other treatments such as use of organic acids or sanitizer solutions, has found to be a promising approach to maintain the microbiological safety and quality of fresh and fresh-cut produce. Recent advances in using UV as a part of hurdle technology on the safety of fresh produce at different stages are presented here. Furthermore, this review discusses the mechanism of UV induced antimicrobial activity, factors that influence antimicrobial efficacy and its effect on produce. In addition, the challenges, and prospects of using UV irradiation as an intervention treatment were also discussed.

Combination of ultrasound-peracetic acid washing and ultrasound-assisted aerosolized ascorbic acid: A novel rinsing-free disinfection method that improves the antibacterial and antioxidant activities in cherry tomato

Traditional ultrasound (US)-assisted disinfection is only effective during washing. Coating is an effective method to control microbial growth after washing; however, cross-contamination can occur during immersion in the coating aqueous solution. Tap water (TW) rinsing is generally used to remove sanitizer residues after US-assisted washing; however, the Food and Drug Administration stated that rinsing is unnecessary when the peracetic acid (PAA) concentration does not exceed 80 ppm. In this study, we proposed a novel US-assisted hurdle technology of 80 ppm PAA combined with low-frequency US (25 kHz) during washing, followed by US-assisted aerosolization processing (nonimmersion coating). Ascorbic acid (AA), a safe and low-cost agent, was selected as the aerosolization solution. Cherry tomatoes were selected as the model, and the proposed method was compared with traditional US-assisted disinfection methods (US-10 ppm free chlorine washing + TW rinsing and US-5 ppm chlorine dioxide washing + TW rinsing) to analyze the disinfection efficacy and quality changes. During storage, US-PAA + 1%AA facilitated additional 0.7-0.9, 0.6-0.8, 0.7-1.0, and 0.5-1.0 log CFU/g reductions in the counts of Escherichia coli O157:H7, Salmonella Typhimurium, aerobic mesophilic counts, and molds and yeasts, respectively, as compared with traditional US-assisted methods. Sensory properties, color index, total soluble solids, titratable acidity, and weight loss were not negatively affected by any of the treatments. Firmness was slightly reduced after all treatments; however, the firmness of the samples was maintained during storage, in contrast with the decreased firmness observed in the control. Phenolic content and antioxidant activity significantly increased after all treatments. Further analysis of two key enzymes (phenylalanine ammonia-lyase and 4-coumarate-CoA ligase) involved in phenolic synthesis showed that their levels significantly increased following all treatments, leading to an increase in phenolic content and antioxidant activity. This result also indicated that US-assisted washing could act as an abiotic elicitor to increase nutritional content. Overall, US-PAA + 1%AA treatment served as an effective method for disinfecting produce during washing and for controlling microbial growth after washing without prolonging the processing time, which is an advantage over traditional US-assisted washing.

Efficacy of a Mixed Peroxyorganic Acid Antimicrobial Wash Solution against Salmonella, Escherichia coli O157:H7, or Listeria monocytogenes on Cherry Tomatoes

ABSTRACT

A study was conducted to evaluate a new organic mixed peroxyacid solution produce wash composed of a combination of organic acids (lactic acid and one or more fruit acids) and hydrogen peroxide for activity against foodborne pathogens. The mixed peroxyacid was challenged against Salmonella enterica, Escherichia coli O157:H7, and Listeria monocytogenes in suspension or on the surface of dip-inoculated cherry tomatoes. Cherry tomatoes were also treated with 8 ppm of free chlorine in the form of sodium hypochlorite. When tested against planktonic cells of Salmonella and E. coli O157:H7 in pure culture for 120 s, these pathogens were reduced by 7.5 and 7.1 log CFU/mL, respectively, by the 0.40% peroxyacid solution, and L. monocytogenes was decreased by 5.0 log CFU/mL by the 0.80% solution. When cherry tomatoes were dip inoculated and treated with 8 ppm of free chlorine, Salmonella and E. coli O157:H7 populations decreased by 2.5 and 2.6 log CFU/g, respectively; these reductions were not significantly different from those obtained after sterile water rinses. However, the 1.0% peroxyacid solution reduced the same microorganisms by 3.8 and 3.4 log CFU/g, respectively, which was significantly greater (P < 0.05) than the reductions achieved by the 2-min sterile water rinse. For tomatoes dip inoculated with L. monocytogenes, populations were reduced by 3.5 log CFU/g by the 1.0% peroxyacid solution, which was significantly greater (P < 0.05) than reductions achieved by 8 ppm of free chlorine (2.6 log CFU/g) or sterile water (1.7 log CFU/g). These results indicate that this peroxyacid combination is an effective organic antimicrobial agent for preventing cross-contamination during the washing of cherry tomatoes and can inactivate S. enterica, E. coli O157:H7, and L. monocytogenes by up to 3.8, 3.4, and 3.5 log CFU/g, respectively.

HIGHLIGHTS

Pre-oxidation of spent lettuce wash water by continuous Advanced Oxidation Process to reduce chlorine demand and cross-contamination of pathogens during post-harvest washing

A continuous Photo-Fenton Advanced-Oxidation-Process (AOP) for reducing the chlorine-demand of spent lettuce wash water was developed based on the generation of hydroxyl-radicals from the UV-C degradation of hydrogen peroxide in the presence of ferric-catalyst. It was found that an interaction between UV-C and hydrogen peroxide or ferric-catalyst concentration was associated with high hydroxyl-radical generation as determined from the oxidation of methylene blue. The optimal AOP treatment was identified as 320 mJ/cm2 UV-C dose, 9.6 mg/L H2O2, and 9 mg/L ferric-catalyst. When the treatment was applied to simulated lettuce spent wash water (6.6 g romaine lettuce per liter of distilled water containing 100 mg bentonite; pH 6.9) the chlorine demand was reduced from 150 ppm to 130 ppm. The chlorination of AOP treated water did not result in a greater log reduction of pathogens (Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella) on lettuce but did reduce cross-contamination between batches during washing. The chlorinated byproducts formed in AOP treated water exhibited higher antimicrobial activity compared to untreated controls. Although the treatment was successful in reducing cross-contamination of lettuce batches the cytotoxicity of disinfection byproducts requires to be assessed.

Evaluation of Potential Impacts of Free Chlorine during Washing of Fresh-Cut Leafy Greens on Escherichia coli O157:H7 Cross-Contamination and Risk of Illness

Addition of chlorine-based antimicrobial substances to fresh-cut leafy green wash water is done to minimize microbial cross-contamination during processing. We developed the FDA Leafy Green Risk Assessment Model (FDA-LGRAM) to quantify the impact of free chlorine concentration in wash water during fresh-cut lettuce processing on the extent of water-mediated cross-contamination between shredded lettuce and the associated risk of illness due to exposure to Escherichia coli O157:H7. At different contamination prevalence and levels of E. coli O157:H7 on incoming lettuce heads, the model compared the predicted prevalence of contaminated fresh-cut lettuce packages and the risk of illness per serving between: (1) a scenario where fresh-cut lettuce was packaged without washing; and (2) scenarios involving washing fresh-cut lettuce with different levels of free chlorine (0 ppm, 5 ppm, 10 ppm, 15 ppm, and 20 ppm) prior to packaging. Our results indicate that the free chlorine level in wash water has a substantial impact on the predicted prevalence of contaminated fresh-cut lettuce packages and the risk of illness associated with E. coli O157:H7 in fresh-cut lettuce. Results showed that the required level of free chlorine that can minimize water-mediated cross-contamination and reduce the corresponding risk of illness depended on contamination prevalence and levels of E. coli O157:H7 on incoming lettuce heads. Our model also indicated that the pathogen inactivation rate in wash water via free chlorine was a key model parameter that had a significant impact on the extent of cross-contamination during washing and the predicted associated risk of illness.

The antimicrobial interventions of cilantro (Coriandrum sativum) in mitigating cross-contamination of foodborne pathogens during the retail soaking process

The efficacy of commercially available antimicrobials for fresh produce, electrolyzed water (EW; ca. 60 mg/L of free chlorine), a combination of lactic acid and phosphoric acid-based (LPA), and citric acid-based (CA) was compared with tap water (TW) in preventing cross-contamination during the soaking step of crisping at a retail setting. A bunch of cilantro (103.7 ± 14.9 g/bunch) was inoculated with 3-strain cocktail of nalidixic acid-resistant Salmonella enterica and E. coli O157:H7, S. enterica and Listeria monocytogenes, or E. coli O157:H7 and L. monocytogenes (ca. 5.0 log CFU/g). One inoculated and seven non-inoculated cilantro bunches were soaked in 76 L of TW, EW, LPA, and CA for five minutes. Two additional soakings, each with eight bunches of non-inoculated cilantro were performed in the same soaking water. To determine the cross-contamination of inoculated foodborne pathogens via soaking water, the cilantro samples and soaking water following each soaking step were subjected to microbiological analyses using selective media supplemented with nalidixic acid (100 μg/mL). During the first soaking, significantly greater reductions in Salmonella (2.9 ± 0.5 log CFU/g), E. coli O157:H7 (3.0 ± 0.1), and L. monocytogenes (2.7 ± 0.3) on cilantro were achieved with EW compared to soaking with TW, LPA, and CA (P &lt; 0.05). Cross-contamination of foodborne pathogens from inoculated cilantro to non-inoculated cilantro was completely mitigated by EW during three subsequent soaking events. With the exception of TW soaking water, no inoculated foodborne pathogens were detected in the 100 mL soaking water of EW, CA, and LPA collected. Including an appropriate concentration of chemical antimicrobial in water during the soaking step of crisping aids in mitigating cross-contamination of foodborne pathogen(s) in cilantro bunches.

Combined use of ultrasound-assisted washing with in-package atmospheric cold plasma processing as a novel non-thermal hurdle technology for ready-to-eat blueberry disinfection

Ultrasound (US) has limited disinfection efficacy, and it has been recommended to combine it with chemical disinfectants during fresh produce washing. After washing and before packaging, the disinfection effect of US-assisted washing can be weakened; thus, in-package disinfection is important. As a nutritious fruit, there are no packaged blueberries can be directly eaten. Therefore, in this study, blueberry was selected as the model, and the two most commonly used disinfectants (free chlorine [FC] at 10 ppm and peracetic acid [PAA] at 80 ppm) were combined with low-frequency US (25 kHz) during washing, followed by in-package disinfection using dielectric barrier discharge cold plasma (CP). The disinfection efficacy of US-FC and US-PAA against Escherichia coli O157:H7 and Salmonella Typhimurium was significantly higher than that of US, PAA, or FC alone. The highest disinfection efficacy of CP was observed at the pulse frequency range of 400-800 Hz. For US-FC (1 min) + CP (1 min), an additional 0.86, 0.71, 0.42, and 0.29 log CFU/g of reduction for E. coli O157:H7, S. Typhimurium, aerobic mesophilic counts, and mold and yeast was achieved, respectively, compared with US-FC (2 min) alone. For US-PAA (1 min) + CP (1 min) an additional 0.71, 0.59, 0.32, and 0.21 log CFU/g of reduction was achieved for the above organisms, respectively, compared with US-PAA (2 min) alone. Quality loss (in total color difference, firmness, and anthocyanin content) was not observed after treatment with US-FC + CP, US-PAA + CP, US-FC, or US-PAA. After treatment with US-FC + CP or US-PAA + CP, the reactive oxygen species (ROS) content was significantly lower than that in the other groups, and antioxidant enzyme activity was significantly higher than that in the other groups, suggesting that in-package CP can activate the blueberry antioxidant system to scavenge ROS, thereby lowering the risk of quality loss. US-CP combination not only improves the disinfection efficacy but also lowers quality loss caused by ROS, without prolonging the processing time.

Use of aqueous ozone rinsing to improve the disinfection efficacy and shorten the processing time of ultrasound-assisted washing of fresh produce

In minimal processing industry, chlorine is widely used in the disinfection process and ultrasound (US) increases the disinfection efficacy of chlorine and reduces the cross-contamination incidence during washing. Tap water (TW), which has no disinfection effect, is generally used to rinse off sanitizer residues on the surface of disinfected fresh-cut vegetables. In this study, aqueous ozone (AO), a low-cost and residue-free sanitizer, was used to replace TW rinsing in combination with US (28 kHz)-chlorine (free chlorine [FC] at 10 ppm, a concentration recommended for industrial use) for the disinfection of fresh-cut lettuce as a model. US-chlorine (40 s) + 2.0 ppm AO (60 s) treatment resulted in browning spots on lettuce surface at the end of storage. In contrast, US-chlorine (40 s) + 1.0 ppm AO (60 s) did not lead to deterioration of the sensory quality (sensory crispness, color, and flavor) and a change in total color difference, and the activities of browning-related enzymes were significantly lower. Moreover, US-chlorine (40 s) + 1.0 ppm of AO (60 s) treatment led to significantly lower counts of Escherichia coli O157:H7, Salmonella Typhimurium, aerobic mesophilic (AMC), and molds and yeasts (M&Y) on days 0-7 than US-chlorine (60 s) + TW (60 s) and single 1.0 ppm AO (120 s) treatments, suggesting that AO provided an additional disinfection effect over TW, while reducing the overall processing time by 20 s. Cell membrane permeability analysis (alkaline phosphatase, protein, nucleotide, and adenosine triphosphate leakage) showed that the combination with 1.0 ppm AO caused more severe cell membrane damage in E. coli O157:H7 and S. Typhimurium, explaining the higher disinfection efficacy. 16S rRNA sequencing revealed that following US-chlorine (40 s) + 1.0 ppm of AO (60 s) treatment, Massilia and Acinetobacter had higher relative abundances (RAs) on day 7 than after US-chlorine (60 s) + TW (60 s) treatment, whereas the RAs of Escherichia-Shigella was significantly lower, indicating that the former treatment has a superior capacity in maintaining a stable microbial composition. This explains from an ecological point of view why US-chlorine (40 s) + 1.0 ppm of AO (60 s) led to the lowest AMC and M&Y counts during storage. The study results provide evidence that AO has potential as an alternative to TW rinsing to increase the disinfection efficacy of US-chlorine.