Growth of Listeria monocytogenes in fresh vegetables and vegetable salad products: An update on influencing intrinsic and extrinsic factors.

The ability of foodborne pathogens to grow in food products increases the associated food safety risks. Listeria monocytogenes (Lm) is a highly adaptable pathogen that can survive and grow under a wide range of environmental circumstances, including otherwise inhibitory conditions, such as restrictive cold temperatures. It can also survive long periods under adverse environmental conditions. This review examines the experimental evidence available for the survival and growth of Lm on fresh vegetables and ready-to-eat vegetable salads. Published data indicate that, depending on certain intrinsic (e.g., nutrient composition) and extrinsic factors (e.g., storage temperature, packaging atmosphere), Lm can survive on and in a wide variety of vegetables and fresh-cut minimally processed vegetable salads. Studies have shown that temperature, modified atmosphere packaging, relative humidity, pH, water activity, background microbiota of vegetables, microbial strain peculiarities, and nutrient type and availability can significantly impact the fate of Lm in vegetables and vegetable salads. The influence of these factors can either promote its growth or decline. For example, some studies have shown that background microbiota inhibit the growth of Lm in vegetables and minimally processed vegetable salads, but others have reported a promoting, neutral, or insignificant effect on the growth of Lm. A review of relevant literature also indicated that the impact of most influencing factors is related to or interacts with other intrinsic or extrinsic factors. This literature synthesis contributes to the body of knowledge on possible strategies for improving food safety measures to minimize the risk of Lm-associated foodborne outbreaks involving vegetables and vegetable salads.

Microbiological quality and safety of minimally processed parsley (Petroselinum crispum) sold in food markets, southeastern Brazil.

AIMS: This study evaluated the microbiological quality and safety of minimally processed parsley sold in southeastern Brazilian food markets. METHODS AND RESULTS: One hundred samples were submitted to the enumeration of Enterobacteriaceae by plating on MacConkey agar. Colonies of Enterobacteriaceae were randomly selected and identified by MALDI-TOF MS. Samples were also tested for Listeria monocytogenes and Salmonella sp. The mean count of Enterobacteriaceae was 6·0 ± 1·0 log CFU per gram, while 18 genera (including 30 species) of bacteria belonging to this family were identified. Salmonella and L. monocytogenes were not detected, while L. innocua was found in two samples and L. fleischmannii was found in one sample. Moreover generic Escherichia coli was found in three samples, all from different brands of minimally processed parsley. CONCLUSIONS: Even though microbial pathogens were not isolated, a variety of indicator micro-organisms were identified, including vegetable spoilers and species capable of causing human opportunistic infections. These results suggest hygienic failures and/or lack of temperature control during processing and storage of these ready-to-eat products. SIGNIFICANCE AND IMPACT OF STUDY: This study highlights the need for control measures during the production chain of minimally processed parsley in order to reduce microbial contamination and the risks of foodborne diseases.

Assessment of the microbiological quality and safety of minimally processed vegetables sold in Piracicaba, SP, Brazil.

The present study shows the results of the microbiological quality and safety of minimally processed vegetables sold in supermarkets and grocery stores located in the city of Piracicaba, SP, Brazil. A total of 100 samples were collected and submitted to enumeration of total coliforms, coliforms at 45°C and generic Escherichia coli using the standard most probable number (MPN) method, in addition to enumeration of total Enterobacteriaceae by plating on MacConkey agar. Moreover, colonies of Enterobacteriaceae were randomly selected and submitted to identification on a MALDI-TOF MS Biotyper™. Samples were also tested for Salmonella spp. according to the ISO 6579:2002 method. The mean count of total coliforms was 2·9 ± 0·5 log MPN per g. For coliforms at 45°C, 20 samples were positive (mean 1·5 ± 1·0 log MPN per g). Generic E. coli was detected in 16 samples (mean 1·4 ± 0·9 log MPN per g) and only one was positive for Salmonella. The mean count of total Enterobacteriaceae was 6·5 ± 1·2 log CFU per g and the most frequent genera identified by MALDI-TOF were Enterobacter (25·9%), Pantoea (9·6%) and Rahnella (9·0%). Overall, results point to poor microbiological quality of a few samples, indicating hygiene failure during their processing. This can pose health risks to consumers, mainly because these products were labelled as sanitized and marketed as ready-to-eat. SIGNIFICANCE AND IMPACT OF THE STUDY: In this study, the microbiological quality and safety of minimally processed vegetables sold in the city of Piracicaba, SP, Brazil, were evaluated through the detection of Salmonella spp., generic Escherichia coli and other Enterobacteriaceae. The results obtained point to poor microbiological quality and safety of a few samples, as generic E. coli was detected in 16 out of 100 samples and Salmonella was isolated from one of them. This indicates hygiene failures during their processing and health risk to consumers, since these products are usually sold as ready-to-eat and typically require no further heat treatment before consumption.

Antimicrobial susceptibility and sessile behaviour of bacteria isolated from a minimally processed vegetables plant.

In this study, 20 heterotrophic bacteria from a minimally processed vegetables (MPV) plant were tested for their susceptibilities to five antibiotics (tetracycline, erythromycin, ampicillin, levofloxacin and ciprofloxacin), their (co)aggregation abilities and their survival under gastric simulated conditions. Peracetic acid (PA) and sodium hypochlorite (SH), both at 50 ppm, were evaluated for their abilities to control biofilms of these bacteria. In general, the Gram-negative bacteria were found to be more resistant to the selected antibiotics. Two isolates, Rhanella aquatilis and Stenotrophomonas maltophilia, demonstrated multidrug resistance. Only Rhodococcus erythropolis presented aggregation potential, while no bacterium survived under the gastric conditions. The biofilm experiments showed PA as less efficient than SH in killing biofilms and neither of the disinfectants was able to fully eliminate the biofilms. Significant regrowth was observed for most of the biofilms. The results indicate that alternative and/or complementary disinfection strategies are required to guarantee food safety.

Effect of thyme essential oil and Lactococcus lactis CBM21 on the microbiota composition and quality of minimally processed lamb's lettuce.

The main aim of this work was to evaluate, at pilot scale in an industrial environment, the effects of the biocontrol agent Lactococcus lactis CBM21 and thyme essential oil compared to chlorine, used in the washing step of fresh-cut lamb's lettuce, on the microbiota and its changes in relation to the time of storage. The modification of the microbial population was studied through pyrosequencing in addition to the traditional plate counts. In addition, the volatile molecule and sensory profiles were evaluated during the storage. The results showed no significant differences in terms of total aerobic mesophilic cell loads in relation to the washing solution adopted. However, the pyrosequencing data permitted to identify the genera and species able to dominate the spoilage associations over storage in relation to the treatment applied. Also, the analyses of the volatile molecule profiles of the samples during storage allowed the identification of specific molecules as markers of the spoilage for each different treatment. The sensory analyses after 3 and 5 days of storage showed the preference of the panelists for samples washed with the combination thyme EO and the biocontrol agent. These samples were preferred for attributes such as flavor, acceptability and overall quality. These results highlighted the effect of the innovative washing solutions on the quality of lettuce through the shift of microbiota towards genera and species with lower potential in decreasing the sensory properties of the product.

Assessing the effect of sodium dichloroisocyanurate concentration on transfer of Salmonella enterica serotype Typhimurium in wash water for production of minimally processed iceberg lettuce (Lactuca sativa L.).

UNLABELLED: This study evaluated the impact of sodium dichloroisocyanurate (5, 10, 20, 30, 40, 50 and 250 mg l(-1) ) in wash water on transfer of Salmonella Typhimurium from contaminated lettuce to wash water and then to other noncontaminated lettuces washed sequentially in the same water. Experiments were designed mimicking the conditions commonly seen in minimally processed vegetable (MPV) processing plants in Brazil. The scenarios were as follows: (1) Washing one inoculated lettuce portion in nonchlorinated water, followed by washing 10 noninoculated portions sequentially. (2) Washing one inoculated lettuce portion in chlorinated water followed by washing five noninoculated portions sequentially. (3) Washing five inoculated lettuce portions in chlorinated water sequentially, followed by washing five noninoculated portions sequentially. (4) Washing five noninoculated lettuce portions in chlorinated water sequentially, followed by washing five inoculated portions sequentially and then by washing five noninoculated portions sequentially in the same water. Salm. Typhimurium transfer from inoculated lettuce to wash water and further dissemination to noninoculated lettuces occurred when nonchlorinated water was used (scenario 1). When chlorinated water was used (scenarios 2, 3 and 4), no measurable Salm. Typhimurium transfer occurred if the sanitizer was ≥10 mg l(-1) . Use of sanitizers in correct concentrations is important to minimize the risk of microbial transfer during MPV washing. SIGNIFICANCE AND IMPACT OF THE STUDY: In this study, the impact of sodium dichloroisocyanurate in the wash water on transfer of Salmonella Typhimurium from inoculated lettuce to wash water and then to other noninoculated lettuces washed sequentially in the same water was evaluated. The use of chlorinated water, at concentration above 10 mg l(-1) , effectively prevented Salm. Typhimurium transfer under several different washing scenarios. Conversely, when nonchlorinated water was used, Salm. Typhimurium transfer occurred in up to at least 10 noninoculated batches of lettuce washed sequentially in the same water.

Application of edible coating with starch and carvacrol in minimally processed pumpkin.

The present study evaluated the effect of an edible coating of cassava starch and carvacrol in minimally processed pumpkin (MPP). The minimal inhibitory concentration (MIC) of carvacrol against Escherichia coli, Salmonella enterica serotype Typhimurium, Aeromonas hydrophila, and Staphylococcus aureus was determined. The edible coating that contained carvacrol at the MIC and 2 × MIC was applied to MPP, and effects were evaluated with regard to the survival of experimentally inoculated bacteria and autochthonous microflora in MPP. Total titratable acidity, pH, weight loss, and soluble solids over 7 days of storage under refrigeration was also analyzed. MIC of carvacrol was 312 µg/ml. Carvacrol at the MIC reduced the counts of E. coli and S. Typhimurium by approximately 5 log CFU/g. A. hydrophila was reduced by approximately 8 log CFU/g, and S. aureus was reduced by approximately 2 log CFU/g on the seventh day of storage. Carvacrol at the 2 × MIC completely inhibited all isolates on the first day of Storage. coliforms at 35 °C and 45 °C were not detected (< 3 MPN/g) with either treatment on all days of shelf life. The treatment groups exhibited a reduction of approximately 2 log CFU/g in psychrotrophic counts compared with controls on the last day of storage. Yeast and mold were not detected with either treatment over the same period. The addition of carvacrol did not affect total titratable acidity, pH, or soluble solids and improved weight loss. The edible coating of cassava starch with carvacrol may be an interesting approach to improve the safety and microbiological quality of MPP.

Effect of argon-enriched modified atmosphere on the over quality and bioactive compounds of ready-to-use broccoli rabe (Brassica rapa sylvestris L. var. esculenta) during the storage.

This study evaluated the effect of argon-enriched modified atmosphere on the storage extension of ready-to-use broccoli rabe in leaf. Broccoli rabe samples (Brassica rapa sylvestris L. var. esculenta) were packaged in 90% argon and 10% O2 (modified atmosphere packaging 1); 80% argon, 10% CO2 and 10% O2 (modified atmosphere packaging 2) and evaluated for the physicochemical characteristics, microbiological parameters and bioactive compounds (glucosinolates) during the cold storage for 9 days. Results showed significant maintenance of colour, chlorophyll, phenols content and antioxidant activity in modified atmosphere packaging packages with respect to air control ones. An increasing biosynthesis of glucosinolates was observed in all packages to the inductive effect of CO2 produced; the amount of minerals unchanged during the storage. Overall appearance and odour evaluation pointed out a positive effect of argon atmospheres, in particular modified atmosphere packaging 1, for the keeping of the sensory attributes compared to those evaluated in air packaging.

Application of coliphage as biocontrol agent in combination with gamma irradiation to eliminate multi-drug-resistant E. coli in minimally processed vegetables.

Biofilm formation is a rising concern in the food industry. Escherichia coli (E. coli) is one of the most important food-borne pathogens that can survive in food and food-related environments and eventually produce biofilms. This study suggested that both coliphages used were successful in preventing the creation of new biofilms as well as removing existing ones. Confocal laser scanning microscopy verified these findings. According to the findings, neither coliphage survived at 37 °C, but both remained stable at 4 °C and - 20 °C for extended periods of time. The study revealed that both coliphages demonstrated a greater degree of gamma irradiation resistance when compared to E. coli. The study's results indicate that the implementation of a dual method, which incorporates gamma irradiation (1.5 kGy) and coliphage treatment, on various kinds of vegetables that were infected with E. coli, resulted in a significant reduction in bacterial count (surpassing 99.99%) following a 24-h incubation period. Combining gamma irradiation and the coliphage approach was significantly effective at lowering polysaccharide concentrations and proteins in the biofilm matrix. The results revealed that the pairing of gamma irradiation and coliphages acted in conjunction to cause disruptions in the matrix of biofilm, thereby promoting cell removal compared with either of the individual treatments. Ca+ ions strengthen the weak virion interaction with the relevant bacterial host cell receptors during the adsorption process. In conclusion, use of coliphage in combination with gamma irradiation treatment can be applied to improve fresh produce's microbial safety and enhance its storability in supermarkets.

Evaluation of the Efficacy of Antioxidant Extract from Lemon By-Products on Preservation of Quality Attributes of Minimally Processed Radish (Raphanus sativus L.).

The aim of this work was to enhance the use of a food-grade antioxidant extract obtained from lemon processing byproducts (peel, pulp and seeds) to extend the shelf life of minimally processed radishes. The extract (LPE) was previously characterized in terms of total phenolic (6.75 ± 0.34 mg GAE g-1 d.w.) and flavonoid content (2.04 ± 0.09 mg CE g-1 d.w.) and antioxidant activity, and eriocitrin and hesperidin were identified as the most prevalent phenolic compounds by a UHPLC system. The effects of different dipping aqueous solutions (UCR, DRa, DRb) and alginate-based edible coating formulations (CRc, CRd) with and without the antioxidant extract were studied on the quality parameters of minimally processed radishes, characterized regarding their microbiological and physicochemical characteristics for up to 14 days at 3 °C. The coating formulated with LPE delayed the radish respiration process, as well as resulting in less color variation (ΔE < 3) and reduced mesophilic aerobic count values (4.49 ± 1.43 log CFU g-1), proving the effectiveness of LPE as a value-added ingredient in developing post-harvest strategies to prolong the shelf life of minimally processed vegetables. Indeed, coated samples without the extract showed a clear development of rotting, which led to the end of their shelf life on their 7th day of storage.

Specific Microbial Communities Are Selected in Minimally-Processed Fruit and Vegetables according to the Type of Product.

Fruits and vegetables (F&V) products are recommended for the daily diet due to their low caloric content, high amount of vitamins, minerals and fiber. Furthermore, these foods are a source of various phytochemical compounds, such as polyphenols, flavonoids and sterols, exerting antioxidant activity. Despite the benefits derived from eating raw F&V, the quality and safety of these products may represent a source of concern, since they can be quickly spoiled and have a very short shelf-life. Moreover, they may be a vehicle of pathogenic microorganisms. This study aims to evaluate the bacterial and fungal populations in F&V products (i.e., iceberg lettuces, arugula, spinaches, fennels, tomatoes and pears) by using culture-dependent microbiological analysis and high-throughput sequencing (HTS), in order to decipher the microbial populations that characterize minimally-processed F&V. Our results show that F&V harbor diverse and product-specific bacterial and fungal communities, with vegetables leaf morphology and type of edible fraction of fruits exerting the highest influence. In addition, we observed that several alterative (e.g., Pseudomonas and Aspergillus) and potentially pathogenic taxa (such as Staphylococcus and Cladosporium) are present, thus emphasizing the need for novel product-specific strategies to control the microbial composition of F&V and extend their shelf-life.

The Influence of Two-Component Mixtures from Spanish Origanum Oil with Spanish Marjoram Oil or Coriander Oil on Antilisterial Activity and Sensory Quality of a Fresh Cut Vegetable Mixture.

The aim of this study was to evaluate two-component mixtures of essential oils (EOs) in sub-inhibitory concentrations for antilisterial protection of minimally processed vegetables. Spanish origanum oil (SOO), Spanish marjoram oil (SMO) and coriander oil (CO) and a mixture of fresh leafy vegetables with red beet were used. The chemical compositions of selected EOs were analyzed by gas chromatography. Carvacrol was the major component of SOO. The dominant active component of SMO was 1,8-cineole, while the major constituent in CO was linalool. The study shows that essential oils in combination, namely SOO + SMO and SOO + CO in a » MIC + » MIC (Minimal Inhibitory Concentration), have a synergistic effect against L. monocytogenes. The reduction of L. monocytogenes in vegetable mixtures treated by EOs in these selected combinations after 24 h of storage was approximately equal to the limit of detection. Furthermore, it was found that the vegetable mixture treated with SOO + SMO had the highest-rated sensorial quality and could therefore meet consumer expectations.

Fruits and vegetable-processing waste: a case study in two markets at Rio de Janeiro, RJ, Brazil.

Fruits and vegetables (FV) consumed in natura or processed produce a significant volume of waste, causing an economic deficit in the productive chain. FV markets feature a significant production of vegetable residues with potential of use, since they commercialize an increasing amount of minimally processed vegetables and fruit juices. To this end, it is important to identify, quantify, and characterize these wastes and to propose feasible and coherent alternatives for their use at regional and worldwide levels. In this paper, a case study of two FV markets in Rio de Janeiro, Brazil, was conducted to identify and quantify FV processing waste. Over a period of 20 days, the FV residues from 31 vegetables and 17 fruits were identified and weighed. It is estimated by extrapolation that 106,000 kg of FV were processed in 1 year in two units of FV markets and 48.6% of FV were discarded as by-products. This may be a consequence of factors that contribute to waste generation, such as the low preparation and/or training of the manipulators as well as the quality of the equipment and the maintenance thereof. Thus, studies that aim to understand the environmental impact by monitoring the of FV waste are fundamental, since this waste can be used as raw material and converted into value-added products.

Preincubation of Escherichia coli ATCC 25922 with NaCl Increases Its Attachment to Lettuce Surfaces Compared with Other Chemicals.

　The inhibition of microbial attachment to food is important for the prevention of cross-contamination during food processing. The effect of several chemicals that were added in an Escherichia coli growth medium on the attachment of the bacterium to lettuce was investigated. E. coli ATCC 25922, which is reportedly a useful surrogate for E. coli O157:H7 in surface attachment studies, was preincubated in a nutrient broth (NB) containing sodium chloride, potassium chloride, sodium deoxycholate, sodium linear alkylbenzene sulfonate, or sorbic acid. The bacterial cells were placed in contact with cut lettuce in a saline solution at 5℃ for 24 hours. Only the addition of NaCl in the NB influenced the attachment of E. coli, Salmonella enterica subsp. Enteritidis, and Klebsiella pneumoniae to the lettuce. The attachment of E. coli showed the largest significant increase at 2% NaCl. Changes in the attachment levels were not due to surface hydrohobicity or the motility of E. coli cells. Similar results were observed for S. enterica although the variation in the degree of attachment of the latter was quite small. These results suggested that the attachment of E. coli O157:H7 to food surfaces is influenced by the bacterial growth conditions prior to food exposure and prior to the development of the biofilm; furthermore, the environmental NaCl concentration should be controlled during food processing to prevent the cross-contamination of foods with E. coli.

Microbiological and Sensory Quality of Fresh Ready-to-Eat Artichoke Hearts Packaged under Modified Atmosphere.

In recent years the sales of minimally processed vegetables have grown exponentially as a result of changes in consumer habits. The availability of artichoke buds as a ready-to-eat product would be, therefore, highly advantageous. However, minimally processed artichoke hearts are difficult to preserve because of their rapid browning and the proliferation of naturally occurring microorganisms. We developed artichoke hearts prepared as ready-to-eat products that maintain the characteristics of the fresh product. The microbiological stability, sensory qualities, and shelf life of the processed artichoke hearts were determined. During the shelf life, Salmonella, Listeria monocytogenes, and Escherichia coli counts were below the limits legally established by European regulations for minimally processed vegetables. The pH played an important role in microbial growth. Artichoke hearts had lower microbial counts in experiments conducted at pH 4.1 than in experiments conducted at pH 4.4, although the recommended threshold value for total plate count (7 log CFU/g) was not exceeded in either case. Sensory parameters were affected by the microorganisms, and artichoke products at lower pH had better sensory qualities. Vacuum impregnation techniques, modified atmosphere packaging, and low storage temperature were very effective for increasing the shelf life of minimally processed artichokes. The average shelf life was approximately 12 to 15 days.

Modeling growth of Escherichia coli O157:H7 in fresh-cut lettuce treated with neutral electrolyzed water and under modified atmosphere packaging.

The purpose of this study was to evaluate and model the growth of Escherichia coli O157:H7 in fresh-cut lettuce submitted to a neutral electrolyzed water (NEW) treatment, packaged in passive modified atmosphere and subsequently stored at different temperatures (4, 8, 13, 16°C) for a maximum of 27 days. Results indicated that E. coli O157:H7 was able to grow at 8, 13, and 16°C, and declined at 4°C. However at 8°C, the lag time lasted 19 days, above the typical shelf-life time for this type of products. A secondary model predicting growth rate as a function of temperature was developed based on a square-root function. A comparison with literature data indicated that the growth predicted by the model for E. coli O157:H7 was again lower than those observed with other disinfection treatments or packaging conditions (chlorinated water, untreated product, NEW, etc.). The specific models here developed might be applied to predict growth in products treated with NEW and to improve existing quantitative risk assessments.

Microbiological quality of minimally processed vegetables sold in Porto Alegre, Brazil

Minimally processed vegetables go through various steps during their preparation, with many modifications to their natural structure. However, they must maintain the same quality as the fresh produce. The aim of the present study was to quantify mesophilic and psychrotrophic microorganisms and total and faecal coliforms, and to assess the presence of Escherichia coli, parasites, and dirt material in ready-to-eat minimally processed vegetables. Fifty-six samples of minimally processed vegetables were analysed for the presence of mesophilic and psychrotrophic microorganisms by the plate-count method. Monthly means ranged from 4.7x10(5) to 1.6x10(8) CFU/g and from 7.9x10(6) to 2.7x10(8) CFU/g, respectively for mesophilic and psychrotrophic microorganisms. Coliforms were analysed by the multiple-tube method; total coliforms ranged from <3 to ³ 2.4x10(4) MPN/g and faecal coliforms from <3 to 1.1x10(4) MPN/g. Escherichia coli was detected in eight samples. Out of 52 samples, eight (15.3 percent) contained oocysts of Eimeria spp.. Dirt matter, such as insect body parts and young mites, was also found. Contamination of faecal origin was observed in these samples, suggesting that either the sanitisation of the product was unsuccessful, or soil or irrigation water could be the source of these microorganisms.

Hortaliças minimamente processadas passam por várias etapas durante seu processamento, no qual ocorrem várias modificações de sua estrutura natural, todavia elas devem manter a mesma qualidade do produto não processado. O objetivo deste estudo foi quantificar microrganismos mesófilos e psicrótróficos, coliformes totais e fecais e verificar a presença de E. coli, parasitas e sujidades em hortaliças minimamente processadas prontas para consumo. Foram analisadas 56 amostras para mesófilos e psicrotróficos pelo método de contagem em placas, com média mensal 4,7x10(5) a 1,6x10(8) UFC/g e de 7,9x10(6) a 2,7x10(8) UFC/g, respectivamente. Os coliformes foram analisados pela técnica dos tubos múltiplos, onde coliformes totais variaram de <3 a ³ 2,4x10(4) NMP/g e coliformes fecais, de <3 a 1,1x10(4) NMP/g, e E. coli foi observada em oito amostras. De 52 amostras, 8 (15,3 por cento) apresentaram oocistos de Eimeria spp. Sujidades, como fragmentos de insetos e ácaros jovens foram encontrados. Contaminação de origem fecal foi verificada no presente estudo, sugerindo falhas nas etapas do processamento das hortaliças, ou que o solo ou a água de irrigação também poderiam ser fontes de disseminação destes microrganismos.

Avaliação quantitativa do risco de Salmonella e Listeria monocytogenes em vegetais minimamente processados / Quantitative risk assessment of Salmonella and Listeria monocytogenes in minimally processed vegetables

A ocorrência de surtos de doencas associadas aos vegetais minimamente processados (VMP) tem chamado a atenção para a sua segurança microbiológica. A avaliação quantitativa de riscos permite que o impacto das materias-primas e processamento seja avaliado e os resultados obtidos sejam usados para gestão e comunicação do risco. Desta forma, o presente estudo objetivou quantificar o risco de infecções por Salmonella spp. e Listeria monocytogenes a partir do consumo de VMP no Brasil. Um total de quinhentas e doze amostras de VMP foram analisadas e foi possivel enumerar e detectar Salmonella em 0,4% e 0,4% das amostras, respectivamente. L. monocytogenes foi enumerada e detectada em 0,97% e 3,1% das amostras analisadas, respectivamente. Os isolados de Salmonella spp. (n=4) e L. monocytogenes (n=69) foram confirmados por PCR e caracterizados por sorotipagem tradicional. Os isolados de L. monocytogenes foram caracterizados quanto ao ribotipo, resistencia ao cloro, taxa de multiplicação (µ), capacidade de formação de biofilmes e presença de genes de virulência. O sorovar predominante entre Salmonella spp. foi S. Typhimurium. Em relação a L. monocytogenes, observou-se prevalência do sorotipo 4b e do ribogrupo DUP-1038 e presenca de genes de virulência em 100% (inlA) e 97% (inlC e inlJ) dos isolados. A maioria dos isolados de L. monocytogenes foi resistente a exposição a 125 ppm de cloro livre, e todos foram capazes de aderir ao aco inox, atingindo concentracoes acima de 4 log UFC/cm2. Testes-desafio foram conduzidos para determinar o potencial de multiplicação (δ) de cepas de Salmonella e L. monocytogenes em nove diferentes tipos of VMPs armazenados a 7°C e 15°C por 6 dias. O armazenamento a 15°C por 6 dias resultou nos maiores aumentos nas populações de L. monocytogenes em couve picada (δ= 3,34) e rúcula ((δ= 3,22), enquanto para Salmonella, as maiores populações foram observadas em rúcula (δ= 4,05) e escarola (δ= 2,80). Testes-desafios posteriores indicaram que a multiplicação dos dois patógenos em VMP foi mais pronunciada quando os mesmos foram embalados sob atmosfera modificada em comparação a embalagem em filmes perfurados. Modelos preditivos primários e secundários descrevendo a taxa de multiplicação e tempo de lag de Salmonella spp. e L. monocytogenes em VMP em função da temperatura de armazenamento (7, 10, 15, 20, 25 e 30°C) foram gerados. Verificou-se que os modelos gerados apresentaram a precisão necessária e foram adequados para modelagem da multiplicação dos dois patógenos em VMP. Os modelos de avaliação quantitativa de risco (AQR) foram construidos para determinar a probabilidade de infecção por Salmonella spp. e L. monocytogenes devido ao consumo de VMPs. Os modelos construidos com base nos dados levantados da literatura indicaram risco de infecção por Salmonella spp. e L. monocytogenes de 8.66 x 10-3 e 1.87 x 10-8, respectivamente, sendo necessário que medidas de mitigação do risco sejam adotadas

The occurrence of foodborne disease outbreaks linked to minimally processed vegetables (MPV) is concerning industries, consumers and governments worldwide. Quantitative risk assessments can estimate the impact of raw materials and processing practices and these estimates are used for risk management and risk communication. This study aimed at quantifying the risks of infection by Salmonella spp. and Listeria monocytogenes due to consumption of MPV in Brazil. A total of five hundred and twelve samples of MPV were analyzed and Salmonella was detected and enumerated in 0.4% and 0.4% of the samples, respectively. L. monocytogenes was enumerated and detected in 0.97% and 3.1% of the samples analyzed, respectively. Isolates of Salmonella spp. (n=4) and L. monocytogenes (n=69) were confirmed through PCR and characterized by traditional serotyping. The isolates of L. monocytogenes were characterized for their ribotype, resistance to chlorine, growth rate, (µ) and ability to form biofilms and presence of virulence factors. Among Salmonella spp., S. Thyphimurium was the most prevalent serovar. Among L. monocytogenes, prevalence of serotype 4b and ribotype DUP-1038 was observed. Virulence gene inlA was present in 100% of the isolates, and genes inlC and inlJ in 97%. The majority of L. monocytogenes isolates were resistant to up to 125 ppm of free chlorine and all isolates were able to attach to stainless steel coupons, reaching populations of up to 4 log10 CFU/cm2. Challenge tests were carried out to determine the growth potential (δ) of Salmonella and L. monocytogenes in nine types of MPV stored at 7°C and 15°C for 6 days. The storage of MPV at 15°C for 6 days resulted in the greatest increases in L. monocytogenes populations in shredded collard green (δ= 3.34) and arugula (δ= 3.22), whereas for Salmonella, the highest populations were found in arugula (δ= 4.05) and escarole (δ= 2.80). Further challenge tests indicated that multiplication of both pathogens in MPV was more pronounced when these products were packaged under modified atmosphere in comparison to packaging in perforated films. Primary and secondary predictive models describing the growth rate and lag time of Salmonella and L. monocytogenes in MPV as a function of storage temperature (7-30°C) were generated. The generated models were accurate and suitable for modeling the growth of pathogens in MPVs. Quantitative risk assessment (QRA) models were built to determine the probability of infection by Salmonella and L. monocytogenes due to consumption of MPVs. The models built using data available in the literature indicated that the risks of infection by these pathogens were 8.66 x 10-3 and 1.87 x 10-8, respectively, evidencing the need for adoption of risk mitigation measures