The effect of different processing parameters on the efficacy of commercial post-harvest washing of minimally processed spinach and shredded lettuce

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.

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.

Effects of washing with boric acid solutions on residual boric acid content, microbiological load, and quality of fresh-cut spinach

Insufficient disinfection of fresh-cut spinach poses significant health risks, along with potential issues like odor, color changes, and softening during short-term storage. To address these challenges, boric acid solutions were explored as an alternative to chlorine washes, which are known to produce toxic compounds. Among various concentrations, 1 % boric acid exhibited the most effective microbial inactivation, leading to substantial reductions in total mesophilic aerobic bacteria, total yeast and mold, and Enterobacteriaceae counts, with reductions of 1.64, 1.38, and 1.77 logs, respectively. Additionally, washing spinach leaves with this solution for 1 min maintained quality parameters, with enhanced antioxidant activity (55.26 mg kg-1 Trolox equivalent), increased total phenolic content (1214.06 mg kg-1 gallic acid equivalent), retention of chlorophyll a (839.16 mg kg-1), chlorophyll b (539.61 mg kg-1) and ascorbic acid content (264.72 mg kg-1). Mechanical properties such as puncture strength (1.81 N) and puncture distance (52.78 mm) also showed favorable outcomes, alongside optimal moisture content at 89.81 %. Notably, residual boric acid content was lowest in spinach leaves (1252.49 mg kg-1) and highest in the wash water (53.88 mg kg-1) after treatment. Scanning electron microscopy images demonstrated maintained tissue integrity, while Hunter Lab readings indicated minimal color changes post-washing. Additionally, sensory evaluations and various physicochemical analyses further supported the efficacy of boric acid washing. Consequently, washing spinach leaves with a 1 % boric acid solution for 1 min yielded favorable results across multiple quality parameters. These findings suggest the potential of boric acid as a safe and effective alternative disinfectant in the fresh-cut produce industry, highlighting its practical implications for food safety and quality. Future research should focus on exploring long-term effects and optimizing washing protocols for broader applications.

One Health Perspectives on Food Safety in Minimally Processed Vegetables and Fruits: From Farm to Fork

While food markets and food production chains are experiencing exponential growth, global attention to food safety is steadily increasing. This is particularly crucial for ready-to-eat products such as fresh-cut salads and fruits, as these items are consumed raw without prior heat treatment, making the presence of pathogenic microorganisms quite frequent. Moreover, many studies on foodborne illnesses associated with these foods often overlook the transmission links from the initial contamination source. The prevention and control of the dissemination of foodborne pathogens should be approached holistically, involving agricultural production, processing, transport, food production, and extending to final consumption, all while adopting a One Health perspective. In this context, our objective is to compile available information on the challenges related to microbiological contamination in minimally handled fruits and vegetables. This includes major reported outbreaks, specific bacterial strains, and associated statistics throughout the production chain. We address the sources of contamination at each stage, along with issues related to food manipulation and disinfection. Additionally, we provide potential solutions to promote a healthier approach to fresh-cut fruits and vegetables. This information will be valuable for both researchers and food producers, particularly those focused on ensuring food safety and quality.

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.

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.

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

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

Application of a Bacteriophage–Sanitizer Combination in Post-Harvest Control of E. coli O157:H7 Contamination on Spinach Leaves in the Presence or Absence of a High Organic Load Produce Wash

Foodborne illness due to the consumption of contaminated products continues to be a serious public health issue. Bacteriophages might provide a natural and effective way to control and reduce the pathogenic bacterial population on food products. Researchers have conducted various experiments to prove their effectiveness against different pathogens and their ability to act as a natural intervention to control pathogen populations, especially in the food industry. In this study, a cocktail of bacteriophages (phages) was added to wash water in the presence of a high organic load along with commercially used sanitizers (chlorine or Sanidate 5.0) to study the efficacy of the phage–sanitizer combination in the challenge water. It was determined that in the absence of organic loads, the sanitizer by itself or the combination with phages significantly (p < 0.001) reduced the contamination by 3.00–5.00 log CFU/mL. In the presence of organic loads, the sanitizer by itself did not contribute to a significant reduction (p > 0.05) compared to the control. However, the sanitizer–phage combination led to a 3.00-log and 6.00-log reduction (p < 0.001) of the pathogen at the end of 3 and 6 h, respectively, in the presence of high organic loads. Therefore, utilizing a combination treatment (phage–sanitizer) might be one solution to reduce pathogen contamination in the food industry, especially the fresh produce industry, thus providing safe food for consumption.

Effect of peroxyacetic acid treatment and bruising on the bacterial community and shelf-life of baby spinach

The importance of leaf integrity, i.e. the effects of bruising (mechanical damage), and sanitisation with peroxyacetic acid (PAA) on bacterial communities of ready-to-eat baby spinach remains unclear. Two shelf-life studies were conducted at 4 °C to investigate the effect of bruising and sanitisation on the growth of spoilage microorganisms. In the first experiment, both bruising treatments (100% and 40% of leaves) halved shelf life to 12 d, whereas intact leaves had a shelf-life of 23 d. Bruising had no influence on bacterial diversity during shelf-life, though some differences in the relative abundance of minor genera were observed. Pseudomonas and Pantoea were the most dominant bacterial genera, regardless of bruising treatment. High throughput amplicon sequencing also identified other spoilage bacteria including Chryseobacterium, Stenotrophomonas, Bacillus, Sphingobacterium, Erwinia and Flavobacterium. In the second experiment, washing of intact baby spinach with a sanitiser (80 mg/L: PAA) reduced microbial load as determined by aerobic plate count but did not immediately affect the presence/relative abundance of most of the genera of spoilage bacteria observed. During shelf-life, the bacterial diversity of sanitised leaves was significantly lower than on water-washed leaves. Although sanitisation resulted in a higher initial log reduction in microbial load compared to control (portable tap water), sanitisation did not extend the shelf life of baby spinach (23 d). Sanitised spinach had reduced bacterial diversity however, by the end of shelf life, both sanitised and water-washed spinach was dominated by Pseudomonas and Pantoea spoilage bacteria. This study demonstrated for the first time that the shorter shelf life of bruised leaves was related to faster microbial growth rather than changes in bacterial diversity or community composition.

Salmonella inactivation and sponge/microfiber mediated cross-contamination during papaya wash with chlorine or peracetic acid as sanitizer

Imported papayas from Mexico have been implicated in multiple salmonellosis outbreaks in the United States in recent years. While postharvest washing is a critical process to remove latex, dirt, and microbes, it also has the potential of causing cross-contamination by foodborne pathogens, with sponge or other fibrous rubbing tools often questioned as potential harboring or transmitting risk. In this study, Salmonella inactivation and cross-contamination via sponges and microfiber wash mitts during simulated papaya washing and cleaning were investigated. Seven washing treatments (wash without sanitizer; wash at free chlorine 25, 50, and 100 mg/L, and at peracetic acid 20, 40, and 80 mg/L), along with unwashed control, were evaluated, using Salmonella strains with unique antibiotic markers differentially inoculated on papaya rind (serovars Typhimurium, Heidelberg, and Derby) and on wash sponge or microfiber (serovars Typhimurium, Newport, and Braenderup). Salmonella survival and transfer on papaya and on sponge/microfiber, and in wash water were detected using selective plating or enrichment. The washing and cleaning process reduced Salmonella on inoculated papayas by 1.69-2.66 and 0.69-1.74 log for sponge and microfiber cleaning, respectively, with the reduction poorly correlated to sanitizer concentration. Salmonella on inoculated sponge or microfiber was under detection limit (1.00 log CFU/cm²) by plate count, but remained recoverable by selective enrichment. Transference of Salmonella from inoculated papaya to sponge/microfiber, and vice versa, could be detected sporadically by selective enrichment. Sponge/microfiber mediated Salmonella cross-contamination from inoculated to uninoculated papayas was frequently detectable by selective enrichment, but rendered undetectable by wetting sponge/microfiber in sanitizing wash water (FC 25-100 mg/L or PAA 20-80 mg/L) between washing different papaya fruits. Therefore, maintaining adequate sanitizer levels and frequently wetting sponge/microfiber in sanitizing wash water can effectively mitigate risks of Salmonella cross-contamination associated with postharvest washing, especially with regard to the use of sponge or microfiber wash mitts.

Handling of Fresh Vegetables: Knowledge, Hygienic Behavior of Vendors, Public Health in Maputo Markets, Mozambique

In developing countries, markets are the main supply of horticultural products to populations, but this can pose a public health challenge due to the risk of the fecal-oral transmission of gut pathogens. This transmission is strongly associated with inadequate public sanitation or low standards of personal and domestic hygiene, and their prevalence can cause gastrointestinal diseases, which are the third leading cause of death in Mozambique. This study aims at assessing the risk for public health of horticultural products supply chain, from the farmers-vendors to the consumers, in municipal markets in Maputo-City, Mozambique. Surveys (75) were conducted on vendors and an observational analysis was performed in the markets under study. The results showed that 62% of the vendors had access to water from boreholes or artisanal sources and the issue "access to water" was significantly different between markets (p = 0.004). Of the vendors who wash their products (53.3%), only 7.5% use tap-water for this purpose, with the difference in attitudes being statistically significant between vendors in the markets (p = 0.035). The majority (60.4%) said that vegetables and fruits can cause diseases due to pesticides and only 31.3% believe that the diseases may be related to poor hygiene. Despite the vendors' low knowledge of Good Hygiene Practices (GHP), we noticed that women have better practical assimilation of GHP when compared to men (p = 0.008). Although Maputo's markets are struggling to achieve quality hygiene standards in a reliable and sustainable manner, their resources are limited and significantly different (p = 0.044) from market to market, and this problem remains a concern for the public-health authorities of the city. In conclusion, the provision of adequate drinking water and sewage disposal systems, together with education for health of vendors, can reduce the risk of contamination of fresh food by the more common organisms causing diarrhea in children, including intestinal parasites.

Modeling of Free Chlorine Consumption and Escherichia coli O157:H7 Cross-Contamination During Fresh-Cut Produce Wash Cycles

Controlling the free chlorine (FC) availability in wash water during sanitization of fresh produce enhances our ability to reduce microbial levels and prevent cross-contamination. However, maintaining an ideal concentration of FC that could prevent the risk of contamination within the wash system is still a technical challenge in the industry, indicating the need to better understand wash water chemistry dynamics. Using bench-scale experiments and modeling approaches, we developed a comprehensive mathematical model to predict the FC concentration during fresh-cut produce wash processes for different lettuce types (romaine, iceberg, green leaf, and red leaf), carrots, and green cabbage as well as Escherichia coli O157:H7 cross-contamination during fresh-cut iceberg lettuce washing. Fresh-cut produce exudates, as measured by chemical oxygen demand (COD) levels, appear to be the primary source of consumption of FC in wash water, with an apparent reaction rate ranging from 4.74 × 10 - 4 to 7.42 × 10 - 4 L/mg·min for all produce types tested, at stable pH levels (6.5 to 7.0) in the wash water. COD levels increased over time as more produce was washed and the lettuce type impacted the rate of increase in organic load. The model parameters from our experimental data were compared to those obtained from a pilot-plant scale study for lettuce, and similar reaction rate constant (5.38 × 10-4 L/mg·min) was noted, supporting our hypothesis that rise in COD is the main cause of consumption of FC levels in the wash water. We also identified that the bacterial transfer mechanism described by our model is robust relative to experimental scale and pathogen levels in the wash water. Finally, we proposed functions that quantify an upper bound on pathogen levels in the water and on cross-contaminated lettuce, indicating the maximum potential of water-mediated cross-contamination. Our model results could help indicate the limits of FC control to prevent cross-contamination during lettuce washing.

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

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

Transfer and Redistribution of Salmonella Typhimurium LT2 and Escherichia coli O157:H7 during Pilot-Scale Processing of Baby Spinach, Cilantro, and Romaine Lettuce

Several outbreaks of foodborne illness traced to leafy greens and culinary herbs have been hypothesized to involve cross-contamination during washing and processing. This study aimed to assess the redistribution of Salmonella Typhimurium LT2 during pilot-scale production of baby spinach and cilantro and redistribution of Escherichia coli O157:H7 during pilot-scale production of romaine lettuce. Four inoculated surrogate:uninoculated product weight ratios (10:100, 5:100, 1:100, and 0.5:100) and three inoculation levels (103, 101, and 10-1 CFU/g) were used for the three commodities. For each of three trials per condition, 5-kg batches containing uninoculated product and spot-inoculated surrogate products at each ratio and inoculation level were washed for 90 s in a 3.6-m-long flume tank through which 890 L of sanitizer-free, filtered tap water was circulated. After washing and removing the inoculated surrogate products, washed product (∼23, 225-g samples per trial) was analyzed for presence or absence of Salmonella Typhimurium or E. coli O157:H7 by using the GeneQuence Assay. For baby spinach, cilantro, and romaine lettuce, no significant differences ( P > 0.05) in the percentage of positive samples were observed at the same inoculation level and inoculated:uninoculated weight ratio. For each pathogen product evaluated (triplicate trials), inoculation level had a significant impact on the percentage of positive samples after processing, with the percentage of positive samples decreasing, as the initial surrogate inoculation level decreased. The weight ratio of contaminated:noncontaminated product plays an important role: positive samples ranged from 0% to 11.6% ± 2.05% and from 68.1% ± 33.6% to 100% among the four ratios at inoculation of 10-1 and 101 CFU/g, respectively. To our knowledge, this study is the first to assess the redistribution of low levels of pathogens from incoming product to leafy greens during processing and should provide important data for microbial risk assessments and other types of food safety analyses related to fresh-cut leafy greens.

Omics approaches on fresh-cut lettuce reveal global molecular responses to sodium hypochlorite and peracetic acid treatment

BACKGROUND

Lettuce is a leafy vegetable that is extensively commercialized as a ready-to-eat product because of its widespread use in human nutrition as salad. It is well known that washing treatments can severely affect the quality and shelf-life of ready-to-eat vegetables. The study presented here evaluated the effect of two washing procedures on fresh-cut lettuce during storage.

RESULTS

An omics approach was applied to reveal global changes at molecular level induced by peracetic acid washing in comparison with sodium hypochlorite treatment. Microbiological analyses were also performed to quantify total bacterial abundance and composition. The study revealed wide metabolic alterations induced by the two sanitizers. In particular, transcriptomic and proteomic analyses pointed out a number of transcripts and proteins differentially accumulated in response to peracetic acid washing, mainly occurring on the first day of storage. In parallel, different microbiota composition and significant reduction in total bacterial load following washing were also observed.

CONCLUSION

The results provide useful information for the fresh-cut industry to select an appropriate washing procedure preserving fresh-like attributes as much as possible during storage of the end product. Molecular evidence indicated peracetic acid to be a valid alternative to sodium hypochlorite as sanitizer solution. © 2017 Society of Chemical Industry.

Sanitizer efficacy in preventing cross-contamination of heads of lettuce during retail crisping

This study was conducted to provide information regarding mitigation of cross-contamination through the use of sanitizer during crisping at retail outlets. Seven non-inoculated heads and one inoculated head (≈5 log CFU/g) of lettuce were placed into commercial sink filled with 76 L of tap water (TW), electrolyzed water (EW, free chlorine: 43 ± 6 ppm), lactic acid and phosphoric acid-based sanitizer (LPA, pH 2.89), or citric acid-based sanitizer (CA, pH 2.78) and soaked for 5 min. Two subsequent batches (eight non-inoculated heads per batch) were soaked in the same solution. Soaking with EW significantly reduced the population of S. enterica (2.8 ± 1.5 log CFU/g), E. coli O157:H7 (3.4 ± 1.1 log CFU/g), and L. monocytogenes (2.6 ± 0.7 log CFU/g) inoculated on Romaine lettuce compared to TW, LPA, and CA (p < 0.05). On Red leaf lettuce, EW significantly reduced populations of S. enterica and E. coli O157:H7, but not L. monocytogenes compared to other treatments. No significant difference was noted between TW, LPA, and CA in reducing foodborne pathogens (p > 0.05) or preventing cross-contamination. Soaking with EW prevented cross-contamination among lettuce heads and controlled bacterial populations in crisping water for three consecutive batches. EW may be an effective option as a sanitizer to minimizing the cross-contamination of leafy greens during the retail crisping.

Evaluation of Postharvest Washing on Removal of Silver Nanoparticles (AgNPs) from Spinach Leaves

There is increasing use of silver nanoparticles (AgNPs) as pesticides for fruits and vegetables due to the particles' unique antimicrobial and insecticidal properties. However, residual AgNPs in harvested produce may transfer through the food chain and pose a potential risk to public health. The objective of this study is to determine whether postharvest washing can effectively remove AgNPs that had accumulated on fresh produce. Ten microliters of commercially available 40 nm citrate coated AgNPs (0.4 mg/L) was dropped to a (1 × 1 cm(2)) spot on spinach leaves, followed by washing with deionized water (DI water), Tsunami 100 (80 mg/L), or Clorox bleach (200 mg/L). Then, the AgNP removal efficiency of the three treatments was evaluated by surface-enhanced Raman spectroscopy (SERS), scanning electron microscopy (SEM)-energy dispersive spectrometry (EDS), and inductively coupled plasma mass spectrometry (ICP-MS). ICP-MS results showed that deionized water removed statistically insignificant amounts of total Ag (5%), whereas Tsunami 100 and Clorox bleach yielded 21 and 10% decreases in total Ag, respectively (P < 0.05). The increased removal efficiency resulted from AgNP dissolution and Ag(+) release upon contact with the oxidizing agents in Tsunami 100 (peroxyacetic acid, hydrogen peroxide) and Clorox bleach (sodium hypochlorite). According to the SERS results, the deionized water and Tsunami 100 treatments removed nonsignificant amounts of AgNPs. Clorox bleach decreased Ag NPs by >90% (P < 0.05); however, SEM-EDS images revealed the formation of large silver chloride (AgCl) crystals (162 ± 51 nm) on the leaf, which explained the low total Ag removal from ICP-MS. This study indicates current factory washing methods for fresh produce may not be effective in reducing AgNPs (by water and Tsunami 100) and total Ag (by all three means). This highlights the necessity to develop an efficient washing method for NP removal from food surfaces in the future.

Modelling of Changes in Postharvest Quality Parameters of Stored Carrots Subjected to Pre- and Postharvest Treatments

The aim of this study was to develop qualitative models that enable prediction of quality of carrots. A full factorial experiment including preharvest biocatalyst application, dipping treatments and storage temperatures was employed. Eleven different biochemical and microbiological quality parameters of carrot (Daucus carota L.) were investigated. The effects of treatments on the shelf-life were investigated using discriminant analysis (DA). The lower storage temperatures (1°C) maintained the superior quality. Kinetic functions were applied to each parameter using the Levenberg–Marquardt algorithm to characterize the rate of change of quality. DAs significantly (P < 0.001) differentiated between the combined effects of the preharvest biocatalyst treatment and storage temperatures. Four discriminant functions factored the differentiation of the quality attributes based on storage time. The models fit well to the experimental data for storage at 1°C. The second-order reaction equations allowed for prediction of ascorbic acid, sucrose and sugar–hexose ratio. First-order reaction equations that allow estimation of fructose, sucrose equivalent, total coliform and total fungi and O2 were developed. The empirical evidence suggests that freshness was maintained in the carrots until day 14 (P < 0.001). Ascorbic acid, sucrose and sugar–hexose ratio were the most relevant parameters to rapidly detect the postharvest changes following the second-order decay rate.

Behavior of Shiga toxigenic Escherichia coli relevant to lettuce washing processes and consideration of factors for evaluating washing process surrogates

Postharvest processes for fresh produce commonly include washing in water containing antimicrobial chemicals, such as chlorine; however, if the antimicrobials are not present in sufficient levels, washing can promote the spread of contamination that might be present. To understand cross-contamination risk during washing, we tested a collection of Shiga toxigenic Escherichia coli (STEC), including O157:H7 and other non-O157 strains, for certain traits during washing of fresh-cut lettuce, i.e., sensitivity to sublethal chlorine levels and ability to cross-contaminate (detach from and attach to) lettuce in the presence of sublethal chlorine levels. Nonpathogenic E. coli Nissle 1917 (EcN) and Pediococcus pentosaceus lactic acid bacterial species (LAB) were included as potential washing process validation surrogates. As measured by extension of the lag phase of growth in media containing 0.15 ppm of chlorine, chlorine sensitivity varied among the STECs. Cross-contamination was assessed by evaluating transfer of bacteria from inoculated to uninoculated leaves during washing. Without chlorine, similar transfer to wash water and uninoculated leaves was shown. In 1 ppm of chlorine, cross-contamination was not detected with most strains, except for the substantial transfer by a STEC O111 strain and EcN in some replicates. Strain O111 and EcN showed less inactivation in 0.25 ppm of chlorine water compared with O157 (P < 0.05). LAB showed similar transfer and similar chlorine inactivation to O157. Considering together the sublethal chlorine sensitivity and detachment/attachment traits, neither EcN nor LAB displayed optimal characteristics as washing process surrogates for the STEC strains, although further evaluation is needed. This work demonstrated a range of behaviors of STEC strains during lettuce washing and may be helpful in hazard characterization, identifying factors to consider for evaluating washing process efficacy, and identifying phenotypic traits to select surrogates to validate washing processes.

Enhanced surveillance on food-borne disease outbreaks: dynamics of cross-contamination in biocidal wash procedure

Understanding the geographic and temporal spread of food-borne diseases associated with fresh produce is crucial for informing adequate surveillance and control. As a first step towards this goal, we develop and analyze a novel three stage model at the processing/sanitization juncture in the fresh produce supply chain. The key feature of our model is its ability to describe the dynamics of cross-contamination during commercial wash procedures. In general, we quantify the degree of cross-contamination in terms of model parameters. Applying these results in the case of Escherichia coli O157:H7 contamination of fresh-cut romaine lettuce, we identify the mean wash time and free chlorine concentration as critical parameters. In addition to showing how these parameters affect contamination levels, we recommend that in order to prevent potential source misidentification, at least 2.2 mg/L of free chlorine should be used during a wash lasting at least 30s.

Ozonation as a clean technology for fresh produce industry and environment: sanitizer efficiency and wastewater quality

AIMS

Inactivating microbial contaminants in fresh produce commonly uses chlorine washing. The effectiveness of ozone was explored as an alternative to chlorine in produce washing for ensuring microbial safety while maximizing water reusability.

METHODS AND RESULTS

An ozone washing system was designed to permit continuous addition of contaminated produce and the reuse of washing water. The effectiveness of ozonation (<2 mg l(-1) ) was determined using Bacillus subtilis spores as a stricter measure of efficiency with processing time of 10 min. As a comparison, chlorine (c. 100 mg l(-1) ) was tested in parallel. Water quality characteristics, including chemical oxygen demand, total suspended solids, disinfectants concentration and microbial reduction were measured. Ozonation showed an average of 1·56 log reduction of B. subtilis spores on lettuce, while chlorination achieved a 1·30 log reduction. The effluents after ozonation demonstrated improved water quality, both in physicochemical quality and microbial quality compared to chlorination.

CONCLUSION

Aqueous ozone treatment is effective against microbial contaminants on fresh produce and enables extended use of washing water.

SIGNIFICANCE AND IMPACT OF THE STUDY

The results provide significant data about ozone disinfection efficacy and its impact on the water reusability, which can facilitate the ozone utilization in the fresh produce production as an environmental friendly alternative.