A comparison of different chemical sanitizers for inactivating Escherichia coli O157:H7 and Listeria monocytogenes in solution and on apples, lettuce, strawberries, and cantaloupe

Efficacy Evaluation of Chlorine Dioxide and Hypochlorous Acid as Sanitisers on Quality and Shelf Life of Atlantic Salmon (Salmo salar) Fillets

Microbial contamination during seafood processing can often lead to a reduction in shelf life and the possibility of food-borne illnesses. Sanitisation with chlorine-based products during seafood processing is therefore sometimes undertaken. This study compared the effects of two sanitisers, chlorine dioxide (ClO2) and hypochlorous acid (HOCl) at their suggested concentration (5 ppm and 10 ppm; 50 ppm and 100 ppm respectively), on physical, chemical, and microbial qualities of Atlantic salmon (Salmo salar) fillets throughout 7 days of simulated retail display refrigeration. Parameters used for assessment included quality index (QI), drip loss, colour, texture, histology, total volatile base nitrogen (TVB-N), lipid oxidation (malonaldehyde, MDA), pH, and total viable count changes. Results indicated that whilst drip loss increased over the storage time, day 4 and 7 drip loss in both sanitisers decreased significantly compared with the control. There was a linear relationship (R > 0.70) between QI and storage time in all treatments, particularly in regard to skin brightness, flesh odour, and gaping parameters, but treatment differences were not present. Texture parameters including gumminess, chewiness, and hardness increased over time in the control whilst both sanitiser treatments seemed to provide protective effects against texture hardening during storage. The observed softening effects from the sanitiser treatments were aligned with microstructural and cytological changes in the histology results, as evidenced by a reduced fibre-fibre adhesion, myodigeneration, and an increase in interfibrillar space over storage time. Colour, especially chroma (C*), was shown to decrease over time in control, whereas insignificant protective effects were observed in both sanitiser treatments at day 7. Irrespective of treatment and storage time, MDA levels exceeded the acceptable limit on all days, whilst TVB-N levels were below the critical limit. Although pH was influenced by treatment and storage time, the pH was within the normal range. Microbiological results showed that with sanitiser addition, TVC was below the permissible level (106 CFU/g) until day 4 but ClO2 ice (5 ppm), ClO2 (10 ppm), and HOCl (100 ppm) treated fillets all exceeded the limit on day 7. The mixed results on the effect of sanitiser addition on fillet quality and shelf life suggested that further investigation on pathogen reduction, sanitiser introductory method, as well as testing the same treatments in low-fat fish models would be recommended.

The Gamma concept approach as a tool to predict fresh produce supporting or not the growth of L. monocytogenes

Challenge tests are commonly employed to evaluate the growth behavior of L. monocytogenes in food matrices; they are known for being expensive and time-consuming. An alternative could be the use of predictive models to forecast microbial behavior under different conditions. In this study, the growth behavior of L. monocytogenes in different fresh produce was evaluated using a predictive model based on the Gamma concept considering pH, water activity (aw), and temperature as input factors. An extensive literature search resulted in a total of 105 research articles selected to collect growth/no growth behavior data of L. monocytogenes. Up to 808 L. monocytogenes behavior values and physicochemical characteristics were extracted for different fruits and vegetables. The predictive performance of the model as a tool for identifying the produce commodities supporting the growth of L. monocytogenes was proved by comparing with the experimental data collected from the literature. The model provided satisfactory predictions on the behavior of L. monocytogenes in vegetables (>80% agreement with experimental observations). For leafy greens, a 90% agreement was achieved. In contrast, the performance of the Gamma model was less satisfactory for fruits, as it tends to overestimate the potential of acid commodities to inhibit the growth of L. monocytogenes.

Bio-based phenolic branched-chain fatty acid in wash water reduced populations of Listeria innocua on apple fruit

Phenolic branched-chain fatty acid (PBC-FA) emulsion was produced by dissolving it in ethanol and mixing with water (pH 7). The resulting monodispersed emulsion droplets were approximately 200 nm in diameter. The stability of the emulsion was evaluated by storing it at 4 and 20 °C for 30 days. The antimicrobial activity of the PBC-FA emulsion was tested against Escherichia coli and Listeria innocua (8 log CFU/mL) by determining the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) using a microdilution method. The PBC-FA was effective against L. innocua with MIC and MBC of 14.1 μg/mL and caused membrane permeation as determined with SEM and Live/Dead cell assay, but was not effective against E. coli O157:H7 at the tested concentrations (5-250 μg/mL). We also evaluated PBC-FA emulsion's potential to be used as a wash against L. innocua inoculated on apples. The results showed that the 500 μg/mL PBC-FA emulsion with 5 % ethanol had equivalent antimicrobial activity (2-3 logs reductions) against L. innocua as the 20 μg/mL chlorine solution, a commonly used sanitizer. 500 μg/mL PBC-FA emulsion had better antimicrobial efficacy when organic matter (chemical oxygen demand: 9.0 g/L) was present compared to 20 μg/mL of chlorine. The effect of PBC-FA on the quality of the apples, was determined by measuring changes in color, firmness, and soluble solids content over a 14-day storage period at 20 °C. The quality of the apples was not affected by PBC-FA over the 14-day storage period, suggesting that PBC-FA emulsion can be used as a wash for apples without affecting their quality.

Selective Transformation of Micropollutants in Saline Wastewater by Peracetic Acid: The Overlooked Brominating Agents

Peracetic acid (PAA) is an emerging alternative disinfectant for saline waters; HOBr or HOCl is known as the sole species contributing to halogenation reactions during PAA oxidation and disinfection. However, new results herein strongly indicated that the brominating agents (e.g., BrCl, Br2, BrOCl, and Br2O) are generated at concentrations typically lower than HOCl and HOBr but played significant roles in micropollutants transformation. The presence of Cl- and Br- at environmentally relevant levels could greatly accelerate the micropollutants (e.g., 17α-ethinylestraiol (EE2)) transformation by PAA. The kinetic model and quantum chemical calculations collectively indicated that the reactivities of bromine species toward EE2 follow the order of BrCl > Br2 > BrOCl > Br2O > HOBr. In saline waters with elevated Cl- and Br- levels, these overlooked brominating agents influence bromination rates of more nucleophilic constituents of natural organic matter and increase the total organic bromine. Overall, this work refines our knowledge regarding the species-specific reactivity of brominating agents and highlights the critical roles of these agents in micropollutant abatement and disinfection byproduct formation during PAA oxidation and disinfection.

Efficacy of commercial peroxyacetic acid on Vibrio parahaemolyticus planktonic cells and biofilms on stainless steel and Greenshell™ mussel (Perna canaliculus) surfaces

The potential of using commercial peroxyacetic acid (PAA) for Vibrio parahaemolyticus sanitization was evaluated. Commercial PAA of 0.005 % (v/v, PAA: 2.24 mg/L, hydrogen peroxide: 11.79 mg/L) resulted in a planktonic cell reduction of >7.00 log10 CFU/mL when initial V. parahaemolyticus cells averaged 7.64 log10 CFU/mL. For cells on stainless steel coupons, treatment of 0.02 % PAA (v/v, PAA: 8.96 mg/L, hydrogen peroxide: 47.16 mg/L) achieved >5.00 log10 CFU/cm2 reductions in biofilm cells for eight strains but not for the two strongest biofilm formers. PAA of 0.05 % (v/v, PAA: 22.39 mg/L, hydrogen peroxide: 117.91 mg/L) was required to inactivate >5.00 log10 CFU/cm2 biofilm cells from mussel shell surfaces. The detection of PAA residues after biofilm treatment demonstrated that higher biofilm production resulted in higher PAA residues (p < 0.05), suggesting biofilm is acting as a barrier interfering with PAA diffusing into the matrices. Based on the comparative analysis of genomes, robust biofilm formation and metabolic heterogeneity within niches might have contributed to the variations in PAA resistance of V. parahaemolyticus biofilms.

Use of Essential Oil Emulsions to Control Escherichia coli O157:H7 in the Postharvest Washing of Lettuce

Essential oils (EOs) have strong antibacterial properties and can be potential sanitizers to reduce pathogen load and prevent cross-contamination during postharvest washing. The objective of this study was to investigate the efficacy of emulsions containing oregano (OR; Origanum vulgare) and winter savory (WS; Satureja montana) EOs at different concentrations (0.94 and 1.88 µL/mL) and storage times (0 h, 24 h, and 7 days), in reducing Escherichia coli O157:H7 on the surface of three types of lettuce (romaine, crisphead, and butterhead). The EO emulsions were compared with one no-rinse treatment and three rinse treatments using water, 200 ppm chlorine, and 80 ppm peroxyacetic acid (PAA), respectively, in a simulated washing system. The results showed that while the EO emulsions significantly reduced E. coli O157:H7 on crisphead lettuce over time, not all treatments were effective for romaine and butterhead lettuce. The mixture of OR and WS at concentrations of 0.94 and 1.88 µL/mL was found to be the most effective in reducing E. coli O157:H7 on inoculated lettuce, resulting in reductions of 3.52 and 3.41 log CFU/g, respectively. Furthermore, the PAA and the mixture of OR and WS at 1.88 µL/mL effectively limited bacterial cross-contamination close to the detection limit for all lettuce types during all storage times. These results suggest that OR and WS EOs could serve as potential alternatives to chemical sanitizers for postharvest lettuce washing.

Persistence of Silver Nanoparticles Sorbed on Fresh-Cut Lettuce during Flume Washing and Centrifugal Drying

Increased agricultural use of silver nanoparticles (Ag NPs) may potentially lead to residual levels on fresh produce, raising food safety and public health concerns. However, the ability of typical washing practices to remove Ag NPs from fresh produce is poorly understood. This study investigated the removal of Ag NPs from Ag NP-contaminated lettuce during bench-top and pilot-scale washing and drying. Ag NP removal was first assessed by washing lettuce leaves in a 4-L carboy batch system using water containing chlorine (100 mg/L) or peroxyacetic acid (80 mg/L) with and without a 2.5% organic load and water alone as the control. Overall, these treatments removed only 3-7% of the sorbed Ag from the lettuce. Thereafter, Ag NP-contaminated lettuce leaves were flume-washed for 90 s in a pilot-scale processing line using ∼600 L of recirculating water with or without a chlorine-based sanitizer (100 mg/L) and then centrifugally dried. After processing, only 0.3-3% of the sorbed Ag was removed, probably due to the strong binding of Ag with plant organic materials. Centrifugation only removed a minor amount of Ag as compared to flume washing. However, the Ag concentration in the ∼750 mL of centrifugation water was much higher as compared to the flume water, suggesting that the centrifugation water would be preferred when assessing fresh-cut leafy greens for Ag contamination. These findings indicate that Ag NPs may persist on contaminated leafy greens with commercial flume washing systems unable to substantially reduce Ag NP levels.

Inactivation methods for human coronavirus 229E on various food-contact surfaces and foods

Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), the cause of the COVID-19 outbreaks, is transmitted by respiratory droplets and has become a life-threatening viral pandemic worldwide. The aim of this study was to evaluate the effects of different chemical (chlorine dioxide [ClO2] and peroxyacetic acid [PAA]) and physical (ultraviolet [UV]-C irradiation) inactivation methods on various food-contact surfaces (stainless steel [SS] and polypropylene [PP]) and foods (lettuce, chicken breast, and salmon) contaminated with human coronavirus 229E (HCoV-229E). Treatments with the maximum concentration of ClO2 (500 ppm) and PAA (200 ppm) for 5 min achieved >99.9% inactivation on SS and PP. At 200 ppm ClO2 for 1 min on lettuce, chicken breast, and salmon, the HCoV-229E titers were 1.19, 3.54, and 3.97 log10 TCID50/mL, respectively. Exposure (5 min) to 80 ppm PAA achieved 1.68 log10 reduction on lettuce, and 2.03 and 1.43 log10 reductions on chicken breast and salmon, respectively, treated with 1500 ppm PAA. In the carrier tests, HCoV-229E titers on food-contact surfaces were significantly decreased (p < 0.05) with increased doses of UV-C (0-60 mJ/cm2) and not detected at the maximum UV-C dose (Detection limit: 1.0 log10 TCID50/coupon). The UV-C dose of 900 mJ/cm2 proved more effective on chicken breast (>2 log10 reduction) than on lettuce and salmon (>1 log10 reduction). However, there were no quality changes (p > 0.05) in food samples after inactivation treatments except the maximum PAA concentration (5 min) and the UV-C dose (1800 mJ/cm2).

Microbubbles Remove Listeria monocytogenes from the Surface of Stainless Steel, Cucumber, and Avocado

Fresh produce may be contaminated by bacterial pathogens, including Listeria monocytogenes, during harvesting, packaging, or transporting. A low-intensity cavitation process with air being injected into water was studied to determine the microbubbles' efficiency when detaching L. monocytogenes from stainless steel and the surface of fresh cucumber and avocado. Stainless steel coupons (1″ × 2″), cucumber, and avocado surfaces were inoculated with L. monocytogenes (LCDC strain). After 1, 24 or 48 h, loosely attached cells were washed off, and inoculated areas were targeted by microbubbles (~0.1-0.5 mm dia.) through a bubble diffuser (1.0 L air/min) for 1, 2, 5, or 10 min. For steel, L. monocytogenes (48 h drying) detachment peaked at 2.95 mean log reduction after 10 min of microbubbles when compared to a no-bubble treatment. After 48 h pathogen drying, cucumbers treated for 10 min showed a 1.78 mean log reduction of L. monocytogenes. For avocados, L. monocytogenes (24 h drying) detachment peaked at 1.65 log reduction after 10 min of microbubbles. Microbubble applications may be an effective, economical, and environmentally friendly way to remove L. monocytogenes, and possibly other bacterial pathogens, from food contact surfaces and the surfaces of whole, intact fresh produce.

Development of benchmark datasets for text mining and sentiment analysis to accelerate regulatory literature review

In the field of regulatory science, reviewing literature is an essential and important step, which most of the time is conducted by manually reading hundreds of articles. Although this process is highly time-consuming and labor-intensive, most output of this process is not well transformed into machine-readable format. The limited availability of data has largely constrained the artificial intelligence (AI) system development to facilitate this literature reviewing in the regulatory process. In the past decade, AI has revolutionized the area of text mining as many deep learning approaches have been developed to search, annotate, and classify relevant documents. After the great advancement of AI algorithms, a lack of high-quality data instead of the algorithms has recently become the bottleneck of AI system development. Herein, we constructed two large benchmark datasets, Chlorine Efficacy dataset (CHE) and Chlorine Safety dataset (CHS), under a regulatory scenario that sought to assess the antiseptic efficacy and toxicity of chlorine. For each dataset, ∼10,000 scientific articles were initially collected, manually reviewed, and their relevance to the review task were labeled. To ensure high data quality, each paper was labeled by a consensus among multiple experienced reviewers. The overall relevance rate was 27.21% (2,663 of 9,788) for CHE and 7.50% (761 of 10,153) for CHS, respectively. Furthermore, the relevant articles were categorized into five subgroups based on the focus of their content. Next, we developed an attention-based classification language model using these two datasets. The proposed classification model yielded 0.857 and 0.908 of Area Under the Curve (AUC) for CHE and CHS dataset, respectively. This performance was significantly better than permutation test (p < 10E-9), demonstrating that the labeling processes were valid. To conclude, our datasets can be used as benchmark to develop AI systems, which can further facilitate the literature review process in regulatory science.

Listeria monocytogenes Outbreaks Related to Commercially Produced Caramel Apples: Developments in Sanitation, Product Formulation, and Packaging: A Review

ABSTRACT

Prior to a deadly 2014 listeriosis outbreak, caramel apples were not thought to be vehicles for the foodborne pathogen Listeria monocytogenes. The purpose of this review article is to summarize what has been learned from research prompted by this outbreak. This overview includes descriptions of the two L. monocytogenes infection outbreaks related to prepackaged caramel apples and a brief discussion of apple sanitation, the production processes used to make caramel apples, and research on ways to prevent future outbreaks associated with caramel apples. A qualitative analysis of the literature and interviews with current caramel apple manufacturers were conducted. Sanitation, packaging, and storage procedures used by manufacturers in the past may not effectively inactivate L. monocytogenes from contaminated product. Novel apple sanitation methods and product formulations to control L. monocytogenes on caramel apples have been developed and, in some cases, implemented in commercial production.

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Behavior of Silver Nanoparticles in Chlorinated Lettuce Wash Water

ABSTRACT

Use of silver nanoparticles (Ag NPs) in pesticides may lead to residual levels in food crops, thus raising food safety and environmental concerns. Because little is known about Ag NP behavior in wash water during typical commercial washing of fresh produce, this study assessed the temporal changes in Ag NP behavior when exposed to 2 to 100 mg/L free chlorine (Cl2) in simulated lettuce wash water for up to 10 days. Aggregate size and zeta potential of Ag NPs (5 mg/L) were evaluated in the presence and absence of dissolved lettuce extract (DLE, 0.1%), with Ag NPs in deionized water serving as the control treatment. In the presence of chlorine, greater aggregation of Ag NPs occurred over time (49 to 431 nm) compared with the control treatment (P < 0.05). Lower zeta potentials (-39 to -95 mV) were observed in the chlorine-only treatments, likely due to the formation of AgCl particles. Larger aggregates and lower zeta potentials were also observed in DLE (84 to 273 nm and -28 to -32 mV, respectively), as compared with the control treatment. After 7 to 10 days, larger aggregates were seen in the chlorine-only treatments as compared with the DLE treatments, despite lower zeta potentials, probably facilitated by nucleation and crystal growth of AgCl. Transmission electron microscopy with energy dispersive spectroscopy confirmed the formation of AgCl-Ag NP composite particles with chlorine and the embedding of AgCl and Ag NPs in the DLE matrix. Thus, DLE might stabilize and protect Ag NPs from chlorine. These findings indicate that chlorine and plant-released organic material can substantially change the behavior of Ag NPs, which may, in turn, impact both removal from fresh-cut produce during washing and their environmental fate.

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

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

Applications of Essential Oils as Antibacterial Agents in Minimally Processed Fruits and Vegetables—A Review

Microbial foodborne diseases are a major health concern. In this regard, one of the major risk factors is related to consumer preferences for “ready-to-eat” or minimally processed (MP) fruits and vegetables. Essential oil (EO) is a viable alternative used to reduce pathogenic bacteria and increase the shelf-life of MP foods, due to the health risks associated with food chlorine. Indeed, there has been increased interest in using EO in fresh produce. However, more information about EO applications in MP foods is necessary. For instance, although in vitro tests have defined EO as a valuable antimicrobial agent, its practical use in MP foods can be hampered by unrealistic concentrations, as most studies focus on growth reductions instead of bactericidal activity, which, in the case of MP foods, is of utmost importance. The present review focuses on the effects of EO in MP food pathogens, including the more realistic applications. Overall, due to this type of information, EO could be better regarded as an “added value” to the food industry.

Biocontrol of Listeria monocytogenes and Salmonella enterica on Fresh Strawberries with Lactic Acid Bacteria During Refrigerated Storage

Small fruits such as strawberries have been increasingly implicated in outbreaks of foodborne illnesses. Salmonella enterica and Listeria monocytogenes may contaminate strawberries leading to potential public health concern. The objective of this study was to investigate the efficacy of a combined lactic acid bacteria (LAB) treatment of Lactobacillus plantarum and Pediococcus pentosaceus for controlling S. enterica and L. monocytogenes on fresh strawberries during storage at 4°C and 10°C. Strawberries purchased from a local grocery store were separately dip inoculated with Salmonella Newport, Salmonella Tennessee, Salmonella Thompson, or a three-strain cocktail of L. monocytogenes at ∼9 log colony-forming unit (CFU)/mL and allowed to air-dry for 1 h. Inoculated strawberries were then divided into three groups: (1) Control (pathogen alone), (2) Man, Rogosa, Sharpe (MRS) control (dipping in MRS broth), and (3) LAB treatment (dipping in a LAB cocktail of L. plantarum and P. pentosaceus). After treatment, strawberries were stored at 4°C or 10°C for 7 d in vented clamshell containers. Surviving Listeria, Salmonella, and LAB populations on strawberries were determined on 0, 1, 3, and 7 d post-treatment by plating on selective agars. At both 4°C and 10°C, LAB treatment significantly decreased Listeria populations by up to 2 log CFU/g compared to controls after 3 d of storage (p < 0.05). When strawberries were stored at 4°C, LAB treatment reduced ∼2.5 log, ∼2.7 log, and ∼2.9 log CFU/g in Salmonella Newport, Salmonella Tennessee, and Salmonella Thompson populations, respectively, compared to control on day 7. Similarly, ∼2.5 log CFU/g reductions of Salmonella populations were observed with LAB treatment at 10°C on day 7. LAB populations remained at ∼7.5 log CFU/g levels on strawberries at both temperatures throughout the entire study. Results of this study suggest that a combined LAB treatment can be potentially used as biocontrol agents against Salmonella and L. monocytogenes on strawberries at postharvest level.

Aqueous chlorine dioxide generated with organic acids have higher antimicrobial efficacy than those generated with inorganic acids

Chlorine dioxide (ClO₂) is commonly generated by mixing sodium chlorite and acid. This study aimed to evaluate how acid affects the release kinetics and antimicrobial property of ClO₂. Solutions made with weak acids released ClO₂ more slowly and had higher stability than those made with hydrochloric acid. Escherichia coli O157:H7, Salmonella Typhimurium, and Listeria monocytogenes were treated with 1, 2.5, and 5 ppm ClO₂ for 3 or 5 min. Lettuce inoculated with the pathogenic bacteria were treated with 2.5 and 5 ppm ClO₂ for 5 min. The effects of peptone load at 0.01% and 0.02% on the antimicrobial efficacy of ClO₂ were investigated in S. Typhimurium cell suspensions. The contribution of acids alone at the pH of the ClO₂ solutions to bacterial reduction was also evaluated. The 2.5 ppm ClO₂ solutions made with citric acid, lactic acid, and malic acid showed higher reductions in all three bacteria than ClO₂ made with hydrochloric acid and sodium bisulfate. The 5 ppm ClO₂ solutions produced with organic acids reduced populations of all bacterial strains from 7 log CFU/mL to undetectable level in 3 min, except S. Typhimurium treated by ClO₂ produced with lactic acid. On inoculated Romaine lettuce model, 5 ppm ClO₂ produced with lactic acid and malic acid resulted in the highest reduction of E. coli O157:H7, S. Typhimurium, and L. monocytogenes of approximately 1.4, 1.7, and 2.4 log CFU/g, respectively. The antimicrobial efficacy of ClO₂ made with HCl and NaHSO₄ were affected by 0.01% and 0.02% peptone load, respectively. Food-grade organic acids produced aqueous ClO₂ solutions with stronger antimicrobial properties than inorganic acids. The acids alone at the pH of ClO₂ did not show significant bacterial reductions.

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

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

Development of Strategies to Minimize the Risk of Listeria monocytogenes Contamination in Radish, Oriental Melon, and Carrots

Contamination by Listeria monocytogenes in packaged produce is a major concern. The purpose of this study was to find natural and affordable sanitizers to reduce L. monocytogenes contamination in agricultural products. Organic acids, ultraviolet-C (UV-C), and ethanol were analyzed either alone or in combination to assess their ability to reduce L. monocytogenes population in radish, oriental melon, and carrot samples. In radish samples, 3% malic acid combined with UV-C at a dosage of 144 mj/cm² significantly reduced (>4 log CFU/g) the population of L. monocytogenes (1.44 ± 0.5) compared to the control sample (5.14 ± 0.09). In the case of the melon samples, exposure to UV-C at a dosage of 144 mj/cm² combined with 3% lactic acid (2.73 ± 0.75) or 50% ethanol (2.30 ± 0.01) was effective against L. monocytogenes compared to the control sample (5.10 ± 0.19). In carrot samples, 3% lactic acid combined with 144 mj/cm² dosage UV-C reduced L. monocytogenes population (4.48 ± 0.25) more than in the control sample (5.85 ± 0.08). These results reveal that sanitizers that are effective for one crop are less effective for another crop indicating that effective prevention methods should be customized for each crop to prevent pathogen cross contamination during postharvest washing.

Kitchen-Scale Treatments for Reduction of Listeria monocytogenes in Prepared Produce

ABSTRACT

Listeriosis, a foodborne illness caused by Listeria monocytogenes, has relatively low incidence, but a substantial mortality rate, particularly in immunocompromised populations. Because of the known risk of L. monocytogenes and other pathogens in produce, immunocompromised individuals are often placed on neutropenic diets that exclude fresh produce. Therefore, this study aimed to evaluate several kitchen-scale treatments as potential interventions to reduce L. monocytogenes in prepared produce. Cucumbers, apples, and celery were dip inoculated with a three-strain cocktail of L. monocytogenes and dried for 24 h. Inoculated products were subjected to the following treatments as applicable: commercial sanitizer soak (90 s, with agitation), tap water rinse (15 s), tap water soak (90 s, with agitation), surface blanching (25 s), tap water rinse (15 s) followed by peeling, and surface blanching (25 s) followed by peeling. In addition, inoculum uptake in celery and the impact of two types of peelers (mechanical crank and manual) were assessed. Treated samples were plated on differential media and incubated for 48 h at 37°C. L. monocytogenes populations were then enumerated and compared with the untreated control (in log CFUs per gram). All treatments lacked efficacy for celery, with reductions significantly less (P < 0.05) than in other products, likely because of inoculum internalization. The sanitizer soak, tap water rinse, and tap water soak did not differ in efficacy (P > 0.05), which was low for cucumbers (<1.5 log CFU/g), apples (<1.3 log CFU/g), and celery (<0.7 log CFU/g). The two types of apple peelers did not differ in efficacy (P > 0.05). Surface blanching and surface blanching followed by peeling were the most effective treatments for both cucumbers and apples (P < 0.05), with average reductions of 4.2 to 5.1 and 3.5 to 5.9 log CFU/g, respectively.

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Fate of Salmonella Typhimurium and Listeria monocytogenes on Whole Papaya during Storage and Antimicrobial Efficiency of Aqueous Chlorine Dioxide Generated with HCl, Malic Acid or Lactic Acid on Whole Papaya

Papaya-associated foodborne illness outbreaks have been frequently reported worldwide. The goal of this study was to evaluate the behavior of Salmonella Typhimurium and Listeria monocytogenes on whole papaya during storage and sanitizing process. Fresh green papayas were inoculated with approximately 7 log CFU of S. Typhimurium and L. monocytogenes and stored at 21 or 7 °C for 14 days. Bacteria counts were determined on day 0, 1, 7, 10 and 14. Fresh green papayas inoculated with approximately 8 log CFU of the bacteria were treated for 5 min with 2.5, 5 and 10 ppm aqueous chlorine dioxide (ClO₂). The ClO₂ solutions were generated by mixing sodium chlorite with an acid, which was HCl, lactic acid or malic acid. The detection limit of the enumeration method was 2.40 log CFU per papaya. At the end of storage period, S. Typhimurium and L. monocytogenes grew by 1.88 and 1.24 log CFU on papayas at 21 °C, respectively. Both bacteria maintained their initial population at inoculation on papayas stored at 7 °C. Higher concentrations of ClO₂ reduced more bacteria on papaya. 10 ppm ClO_2, regardless the acid used to generate the solutions, inactivated S. Typhimurium to undetectable level on papaya. 10 ppm ClO₂ generated with HCl, lactic acid and malic acid reduced L. monocytogenes by 4.40, 6.54 and 8.04 log CFU on papaya, respectively. Overall, ClO₂ generated with malic acid showed significantly higher bacterial reduction than ClO₂ generated with HCl or lactic acid. These results indicate there is a risk of survival and growth for S. Typhimurium and L. monocytogenes on papaya at commercial storage conditions. Aqueous ClO₂ generated with malic acid shows effectiveness in inactivating the pathogenic bacteria on papaya.

Practical in-storage interventions to control foodborne pathogens on fresh produce

Although tremendous efforts have been made to ensure fresh produce safety, various foodborne outbreaks and recalls occur annually. Most of the current intervention strategies are evaluated within a short timeframe (less than 1 h), leaving the behavior of the remaining pathogens unknown during subsequent storages. This review summarized outbreak and recall surveillance data from 2009 to 2018 obtained from government agencies in the United States to identify major safety concerns associated with fresh produce, discussed the postharvest handling of fresh produce and the limitations of current antimicrobial interventions, and reviewed the intervention strategies that have the potential to be applied in each storage stage at the commercial scale. One long-term (up to 12 months) prepacking storage (apples, pears, citrus among others) and three short-term (up to 3 months) postpacking storages were identified. During the prepacking storage, continuous application of gaseous ozone at low doses (≤1 ppm) is a feasible option. Proper concentration, adequate circulation, as well as excess gas destruction and ventilation systems are essential to commercial application. At the postpacking storage stages, continuous inhibition can be achieved through controlled release of gaseous chlorine dioxide in packaging, antimicrobial edible coatings, and biocontrol agents. During commercialization, factors that need to be taken into consideration include physicochemical properties of antimicrobials, impacts on fresh produce quality and sensory attributes, recontamination and cross-contamination, cost, and feasibility of large-scale production. To improve fresh produce safety and quality during storage, the collaboration between researchers and the fresh produce industry needs to be improved.

Synergistic Effects of Lauric Arginate and Peracetic Acid in Reducing Listeria monocytogenes on Fresh Apples

Apples are naturally coated with a water-repelling hydrophobic wax layer, which may limit the antimicrobial efficacies of surface sanitizer solutions. Lauric arginate (LAE) is a cationic surfactant with antimicrobial efficacy against Listeria monocytogenes. In this study, we investigated the antimicrobial and the wettability effects of LAE in enhancing anti-L. monocytogenes efficacy of peracetic acid (PAA) and further verified the optimized treatment combinations in a pilot spray-bar brush bed system. Apples after 48 h of inoculation were treated with PAA surface sanitation in combination with different concentrations of LAE at 22 or 46°C. The effectiveness of PAA with LAE solutions in decontaminating L. monocytogenes significantly increased with the increased concentration of PAA (60-80 ppm) or LAE (0.01-0.05%) or the treatment temperature (from 22 to 46°C). A 30-120-sec wash by 80 ppm PAA with 0.01 and 0.05% LAE at 22°C reduced L. monocytogenes on apples by 2.10-2.25 and 2.48-2.58 log10 CFU/apple, respectively. Including LAE in the PAA solution decreased contact angles on apple surfaces. However, the increased wettability of the sanitizer solution may not be the main contributor to the enhanced antimicrobial efficacy of the PAA solution, given that the addition of Tween 80 or Tween 85 only slightly boosted the anti-L. monocytogenes efficacy of PAA solutions though both increased the wettability of the PAA solutions. The synergistic effects of PAA and LAE were further validated in a pilot spray-bar brush bed packing system, where a 30-sec spray wash with 80 ppm PAA and 0.05% LAE at 22 and 46°C caused 1.68 and 2.08 log reduction of Listeria on fresh apples, respectively. This study provides an improved PAA process/preventive strategy for ensuring microbial food safety of fresh apples that is applicable to commercial apple packing lines.

Prevalence of Listeria Species on Food Contact Surfaces in Washington State Apple Packinghouses

The 2014 caramel apple listeriosis outbreak was traced back to cross-contamination between food contact surfaces (FCS) of equipment used for packing and fresh apples. For Washington state, the leading apple producer in the United States with 79% of its total production directed to the fresh market, managing the risk of apple contamination with Listeria monocytogenes within the packing environment is crucial. The objectives of this study were to determine the prevalence of Listeria spp. on FCS in Washington state apple packinghouses over two packing seasons and to identify those FCS types with the greatest likelihood to harbor Listeria spp. Five commercial apple packinghouses were visited quarterly over two consecutive year-long packing seasons. A range of 27 to 50 FCS were swabbed at each facility to detect Listeria spp. at two sample times, (i) postsanitation and (ii) in-process (3 h of packinghouse operation), following a modified protocol of the FDA's Bacteriological Analytical Manual method. Among 2,988 samples tested, 4.6% (n = 136) were positive for Listeria spp. Wax coating was the unit operation from which Listeria spp. were most frequently isolated. The FCS that showed the greatest prevalence of Listeria spp. were polishing brushes, stainless steel dividers and brushes under fans/blowers, and dryer rollers. The prevalence of Listeria spp. on FCS increased throughout apple storage time. The results of this study will aid apple packers in controlling for contamination and harborage of L. monocytogenes and improving cleaning and practices for sanitation of the FCS on which Listeria spp. are the most prevalent.IMPORTANCE Since 2014, fresh apples have been linked to outbreaks and recalls associated with postharvest cross-contamination with the foodborne pathogen L. monocytogenes These situations drive both public health burden and economic loss and underscore the need for continued scrutiny of packinghouse management to eliminate potential Listeria niches. This research assesses the prevalence of Listeria spp. on FCS in apple packinghouses and identifies those FCS most likely to harbor Listeria spp. Such findings are essential for the apple-packing industry striving to further understand and exhaustively mitigate the risk of contamination with L. monocytogenes to prevent future listeriosis outbreaks and recalls.

Effect of Gaseous Ozone Process on Cantaloupe Melon Peel: Assessment of Quality and Antilisterial Indicators

Fruit waste parts, particularly peel, are abundant sources of bioactive compounds. To be included in the formulation of value-added foods, peel needs to be transformed and subjected to a preservation process. Therefore, this study seeks to assess the effect of ozone on the quality and antilisterial indicators of cantaloupe melon peel paste, aiming at obtaining a product with the potential to be used as a food additive. Ozone was bubbled during 30 and 60 min, and some physicochemical characteristics (soluble solids content, pH and colour), bioactive compounds (total phenolics, chlorophylls and vitamin C) and antioxidant activity were analysed. Peel was also inoculated with Listeria innocua, used as a treatment efficiency indicator. The results indicated that, although ozone negatively affected antioxidant activity, it positively influenced all bioactive compounds analysed. An L. innocua reduction of 1.2 log cycle was achieved after ozone exposure. Ozone should be exploited as a promising technology to assure the quality/safety of cantaloupe melon peel. Indeed, if melon peel is conveniently converted into a suitable form that can be used as a food ingredient, this will promote the valorisation of waste materials with the consequent reduction of industrial by-products and new perspectives for market opportunities.

Synergistic effect of citric acid and xenon light for inactivating foodborne pathogens on spinach leaves

The aim of this study was to evaluate the synergistic antimicrobial effect of xenon light (XL) and citric acid (CA) combination against Escherichia coli O157:H7, Salmonella Typhimurium, and Listeria monocytogenes on spinach leaves and determine the effect of XL-CA combination on quality of spinach leaves. The XL-CA combined treatment for 8 min synergistically decreased the cell counts of E. coli O157:H7 and S. Typhimurium by 5.25 and 5.05 log CFU/cm², respectively, and additively decreased the L. monocytogenes cells by 5.02 log unit on spinach. The mechanisms underlying synergistic lethal effect of the XL-CA combination were investigated. Qualitative and quantitative analyses revealed that the bacterial cell membrane damage was strongly associated with the synergistic antimicrobial effect of the XL-CA combination. Additionally, treatment with XL-CA combination for 8 min did not affect the quality attributes (color, total phenol contents, and texture) of spinach leaves. These results suggest that the XL-CA combination treatment can be effectively used to control major pathogens on fresh produce.

Effect of Chlorine Dioxide Treatment on Human Pathogens on Iceberg Lettuce

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

Postharvest Reduction of Salmonella enterica on Tomatoes Using a Pelargonic Acid Emulsion

A novel produce wash consisting of pelargonic acid (PEL) emulsions was tested on tomatoes contaminated with a five-serovar Salmonella enterica cocktail. Ability to reduce contamination on the inoculated tomato surface, as well as mitigation of subsequent cross-contamination to uninoculated tomatoes washed in re-used/spent wash water were examined. Sanitizer efficacy was also examined over 1 and 7 d storage time (8 °C, recommended for red ripe tomatoes) and in the presence of 0.5% (w/v) organic load. PEL performed statistically the same (p ≤ 0.05) at both 30 mM and 50 mM concentrations and resulted in greater than 1, 5 and 6 log CFU/g Salmonella reductions at 0 h, 1 d and 7 d, respectively, when compared to a water-only or no rinse (NR) treatment. This was also a significantly greater reduction than was observed due to chlorine (sodium hypochlorite) and peroxyacetic acid (PAA) at all time points (p ≤ 0.01). Organic load had no impact on sanitizer efficacy for all examined treatments. Finally, PEL had a deleterious impact on tomato texture. At 1 d, ca. 5 N and 7 N were required to achieve tomato skin penetration and compression, respectively, compared to >9 N and 15 N required by all other treatments (p ≤ 0.05). While PEL sanitizers effectively reduced inoculated Salmonella and subsequent transfer to uninoculated tomatoes, reformulation may be necessary to prevent deleterious quality impacts on produce.

Fresh Produce Safety and Quality: Chlorine Dioxide's Role

Maintaining microbial safety and quality of fresh fruits and vegetables are a global concern. Harmful microbes can contaminate fresh produce at any stage from farm to fork. Microbial contamination can affect the quality and shelf-life of fresh produce, and the consumption of contaminated food can cause foodborne illnesses. Additionally, there has been an increased emphasis on the freshness and appearance of fresh produce by modern consumers. Hence, disinfection methods that not only reduce microbial load but also preserve the quality of fresh produce are required. Chlorine dioxide (ClO₂) has emerged as a better alternative to chlorine-based disinfectants. In this review, we discuss the efficacy of gaseous and aqueous ClO₂ in inhibiting microbial growth immediately after treatment (short-term effect) versus regulating microbial growth during storage of fresh produce (long-term effect). We further elaborate upon the effects of ClO₂ application on retaining or enhancing the quality of fresh produce and discuss the current understanding of the mode of action of ClO₂ against microbes affecting fresh produce.

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

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

Verification of peroxyacetic acid treatment against L. monocytogenes on fresh apples using E. faecium NRRL B-2354 as a surrogate in commercial spray-bar operations

Peroxyacetic acid (PAA) is a commonly used antimicrobial in apple spray bar interventions during post-harvest packing. However, limited information is available about its efficacy against foodborne pathogens on fresh apples under commercial packing conditions. In this study, the practical efficacies of PAA against Listeria monocytogenes on fresh apples during spray bar operation at ambient and elevated temperature were validated in three commercial packing facilities using Enterococcus faecium NRRL B-2354 as a surrogate strain. Apples were inoculated with E. faecium at ~6.5 Log₁₀ CFU/apple and subjected to PAA spray bar interventions per commercial packing line practice. At each temperature and contact time intervention combination, 20-24 inoculated apples were processed together with 72-80 non-inoculated apples. Applying 80 ppm PAA at ambient temperature (17-21 °C) achieved a similar log reduction (P > 0.05) of E. faecium on Granny Smith apples (GSA) in three apple packing facilities, which caused 1.12-1.23 and 1.18-1.32 Log₁₀ CFU/apple reductions of E. faecium on GSA for 30-sec and 60-sec intervention, respectively. Increasing the temperature of the PAA solution to 43-45 °C enhanced its bactericidal effect against E. faecium, causing 1.45, 1.86 and 2.19 Log₁₀ CFU/apple reductions in three packing facilities for a 30-sec contact, and 1.50, 2.24, and 2.29 Log₁₀ CFU/apple reductions for a 60-sec contact, respectively. Similar efficacies (P > 0.05) of PAA at both ambient and elevated temperature were also observed on Fuji apples. Spraying PAA on apples at ambient or elevated temperature reduced the level of E. faecium cross-contamination from inoculated apples to non-inoculated apples but could not eliminate cross-contamination. Data from this study provides valuable technical information and a reference point for the apple industry in controlling L. monocytogenes and verifying the effectiveness of their practices.

Evaluation of azamethiphos and dimethoate degradation using chlorine dioxide during water treatment

Chlorine dioxide (ClO₂) degradation of the organophosphorus pesticides azamethiphos (AZA) and dimethoate (DM) (10 mg/L) in deionized water and in Sava River water was investigated for the first time. Pesticide degradation was studied in terms of ClO₂ level (5 and 10 mg/L), degradation duration (0.5, 1, 2, 3, 6, and 24 h), pH (3.00, 7.00, and 9.00), and under light/dark conditions in deionized water. Degradation was monitored using high-performance liquid chromatography. Gas chromatography coupled with triple quadrupole mass detector was used to identify degradation products of pesticides. Total organic carbon was measured to determine the extent of mineralization after pesticide degradation. Real river water was used under recommended conditions to study the influence of organic matter on pesticide degradation. High degradation efficiency (88-100% for AZA and 85-98% for DM) was achieved in deionized water under various conditions, proving the flexibility of ClO₂ degradation for the examined organophosphorus pesticides. In Sava River water, however, extended treatment duration achieved lower degradation efficiency, so ClO₂ oxidized both the pesticides and dissolved organic matter in parallel. After degradation, AZA produced four identified products (6-chlorooxazolo[4,5-b]pyridin-2(3H)-one; O,O,S-trimethyl phosphorothioate; 6-chloro-3-(hydroxymethyl)oxazolo[4,5-b]pyridin-2(3H)-one; O,O-dimethyl S-hydrogen phosphorothioate) and DM produced three (O,O-dimethyl S-(2-(methylamino)-2-oxoethyl) phosphorothioate; e.g., omethoate; S-(2-(methylamino)-2-oxoethyl) O,O-dihydrogen phosphorothioate; O,O,S-trimethyl phosphorodithioate). Simple pesticide degradation mechanisms were deduced. Daphnia magna toxicity tests showed degradation products were less toxic than parent compounds. These results contribute to our understanding of the multiple influences that organophosphorus pesticides and their degradation products have on environmental ecosystems and to improving pesticide removal processes from water.

Influence of product volume on water antimicrobial efficacy and cross-contamination during retail batch washing of lettuce

Fresh produce shall be thoroughly washed at the retail level prior to serving to the consumer with potable water. Foodborne pathogens if present on a product may transfer to the wash water and cross-contaminate other products immersed in the water. Typically, an entire carton of lettuce (24 heads) is washed together increasing the likelihood of cross-contamination due to the close contact between each head. This study aimed to compare the effects of two wash batch volumes - "low" (8 heads) and "high" (24 heads) on the efficacy of two commercial water antimicrobials and cross-contamination. Red leaf lettuce was spot-inoculated (~5.0 log CFU/g) with Shiga toxin-producing Escherichia coli (STEC) and Listeria monocytogenes. In the first batch of washing, inoculated lettuce was washed with non-inoculated lettuce, followed by reuse of the water/antimicrobials twice washing only non-inoculated lettuce. Samples of inoculated and non-inoculated lettuce were collected to determine aerobic plate count (APC) as well as the populations of STEC and L. monocytogenes. Microbiological analysis of the wash water was also conducted. Wash volume (8 versus 24 lettuce heads) had limited effects on the antimicrobial activities of the interventions evaluated. Instead, high-volume wash increased the rate of cross-contamination between non-inoculated and inoculated lettuce, and cross-contamination of non-inoculated lettuce through wash water reuse. Retailers should consider volume of product processed per batch, reuse of wash water, and use of an appropriate water antimicrobial in consideration of mitigating potential product cross-contamination.

Effectiveness of a peracetic acid solution on Escherichia coli reduction during fresh-cut lettuce processing at the laboratory and industrial scales

Fresh leafy greens like lettuce can be consumed raw and are susceptible to foodborne pathogens if they become contaminated. Recently, the number of reported pathogenic foodborne outbreaks related to leafy greens has increased. Therefore, it is important to try to alleviate the human health burden associated with these outbreaks. Processing of fresh-cut lettuce, including washing, is a step in the supply chain that needs to be well controlled to avoid cross-contamination. Current measures to control the quality of lettuce during washing include the use of chemicals like chlorine; however, questions regarding the safety of chlorine have prompted research for alternative solutions with peracetic acid (PAA). This study evaluates the effectiveness of a PAA (c.a. 75 mg/L) solution on the reduction of a commensal E. coli strain during the washing of fresh-cut lettuce. Experiments were performed at the laboratory scale and validated at the industrial scale. We observed that the use of PAA was not adversely affected by the organic load in the water. The contact time and dose of the PAA showed to be relevant factors, as observed by the approximately 5-log reduction of E. coli in the water. Results showed that once introduced during washing, E. coli remained attached to the lettuce, thus supporting the need to control for pathogenic bacteria earlier in the supply chain (e.g., during primary production) as well as during washing. Moreover, our results showed that the use of PAA during washing did not have an apparent effect on the levels of fluorescent pseudomonads (FP) and total heterotrophic bacteria (THB) in lettuce. Overall, our results at the laboratory and industrial scales confirmed that during the processing of fresh-cut produce, where the accumulation of soil, debris, and other plant exudates can negatively affect washing, the use of a PAA (c.a. 75 mg/L) solution was an effective and safe wash water disinfectant that can potentially be used at the industrial scale.

Exploring the Efficacy and Mechanisms of a Crop Sterilant for Reducing Infestation by Spotted-Wing Drosophila (Diptera: Drosophilidae)

Vinegar flies (Diptera: Drosophilidae) are well known to be associated with yeasts, which provide important nutrients and emit attractive semiochemicals. Drosophila suzukii (Matsumura) has become a major pest of berries and cherries around the world, requiring intensive management to maintain fruit quality. Although insecticides remain a dominant control approach, disruption of fly-yeast-host interactions remains a promising avenue for reducing the economic impact of this pest. We conducted field and laboratory experiments to explore whether a crop sterilant (peroxyacetic acid and hydrogen peroxide) developed for disease control can affect D. suzukii. In 2 yr of field tests in highbush blueberries, we found significantly lower infestation by D. suzukii in plots treated with the crop sterilant, both alone and in a rotation program with zeta-cypermethrin. When shoots from treated plots were tested in no-choice bioassays, crop sterilant treatments did not affect adult mortality or oviposition, but they reduced infestation. To explore the mechanisms in the laboratory, we found that the crop sterilant did not affect adult mortality, nor oviposition on treated fruit under no-choice settings, but adult flies settled and oviposited less on treated fruit in choice settings. When the crop sterilant was applied to colonies of Hanseniaspora uvarum (Niehaus) (Saccharomycetales: Saccharomycodaceae) and Issatchenkia terricola (Van der Walt) (Saccharomycetales: Saccharomycetacea) yeasts that are attractive and provide nutrition to D. suzukii, there was a dose-dependent inhibition of their growth. We highlight the potential for microbial management as a component of integrated pest management programs and prioritize research needs to incorporate this approach into control programs.

The Role of Pathogenic E. coli in Fresh Vegetables: Behavior, Contamination Factors, and Preventive Measures

Many raw vegetables, such as tomato, chili, onion, lettuce, arugula, spinach, and cilantro, are incorporated into fresh dishes including ready-to-eat salads and sauces. The consumption of these foods confers a high nutritional value to the human diet. However, the number of foodborne outbreaks associated with fresh produce has been increasing, with Escherichia coli being the most common pathogen associated with them. In humans, pathogenic E. coli strains cause diarrhea, hemorrhagic colitis, hemolytic uremic syndrome, and other indications. Vegetables can be contaminated with E. coli at any point from pre- to postharvest. This bacterium is able to survive in many environmental conditions due to a variety of mechanisms, such as adhesion to surfaces and internalization in fresh products, thereby limiting the usefulness of conventional processing and chemical sanitizing methods used by the food industry. The aim of this review is to provide a general description of the behavior and importance of pathogenic E. coli in ready-to-eat vegetable dishes. This information can contribute to the development of effective control measures for enhancing food safety.

Reduction of Escherichia coli O157:H7 and naturally present microbes on fresh-cut lettuce using lactic acid and aqueous ozone

Lactic acid (LA) is an effective sanitizer for disinfection of fresh produce. Tap water is generally used to wash disinfected fresh produce because sanitizer residues negatively affect the quality and organoleptic properties of the produce. However, tap water is ineffective for secondary disinfection compared with sanitizers. Thus, we propose a disinfection method using LA plus aqueous ozone (AO), an oxidizing sanitizer that does not lead to secondary residue. We compared the proposed method of 1% LA (90 s) plus 1 mg L-1 AO (30 s) or 2 mg L-1 AO (30 s) with the traditional method of 100 ppm chlorine (120 s) or 1% LA (120 s) plus tap water (30 s) and 2 mg L-1 AO (150 s). Microbial analysis showed that LA plus AO led to the greatest reductions in microbes (Escherichia coli O157:H7, aerobic mesophilic counts, aerobic psychrophilic counts, moulds, and yeasts) during storage (0-5 days at 5 °C). Quality analysis (colour, sensory qualities, electrolyte leakage, polyphenolic content, and weight loss) showed that LA + AO did not cause additional quality loss compared with tap water treatment. These results indicate that the hurdle technology proposed (LA plus AO) has a good potential for use in fresh produce disinfection.

Enhanced Efficacy of Peroxyacetic Acid Against Listeria monocytogenes on Fresh Apples at Elevated Temperature

Peroxyacetic acid (PAA) is the most commonly used antimicrobial in spray bar antimicrobial treatment during fresh apple packing and processing. However, there are limited data regarding its practical efficacy against Listeria monocytogenes on fresh apples. This study evaluated the antimicrobial activity of PAA against L. monocytogenes on fresh apples applicable to current industry practice, and further examined practical parameters impacting its efficacy to maximize the biocidal effects. Apples were inoculated with a three-strain L. monocytogenes cocktail at ~6.0 Log₁₀ CFU/apple and then subjected to comparative antimicrobial treatments after 48 h post-inoculation. An 80 ppm PAA treatment, at 30-s and 2-min exposure, reduced L. monocytogenes on fresh apples by ~1.3 or 1.7 Log₁₀ CFU/apple, respectively. The anti-Listeria efficacy of PAA was not affected by the water hardness and pH of PAA solution, while it improved dramatically when applied at elevated temperature. A 2-min exposure of 80 ppm PAA at 43 and 46°C resulted in a 2.3 and 2.6 Log₁₀ CFU/apple reduction, respectively. A 30-s contact time of 80 ppm PAA at 43-46°C reduced L. monocytogenes on apples by 2.2-2.4 Log₁₀ CFU/apple. Similarly, PAA intervention at elevated temperatures significantly strengthened its effectiveness against naturally occurring apple microbiota. PAA treatment at 43-46°C can provide a vital method to improve antimicrobial efficacy against both L. monocytogenes and indigenous microbiota on fresh apples. Our data provide valuable information and reference points for the apple industry to further validate or verify process controls.