Microbiological contamination of ready-to-eat vegetable salads in developing countries and potential solutions in the supply chain to control microbial pathogens

Antimicrobial Effectiveness of Clove Oil in Decontamination of Ready-to-Eat Spinach (Spinacia oleracea L.)

Due to an increased demand for natural food additives, clove oil was assessed as a natural alternative to chemical disinfectants in produce washing. This study assessed the antimicrobial activity of 5 and 10% (v/v) clove oil-amended wash liquid (CO) using a zone of inhibition (ZIB) test and determined the time required to completely inactivate pathogenic bacteria using bacterial death curve analysis. A washing experiment was used to evaluate CO's ability to inhibit bacterial growth on inoculated RTE spinach and in the wash water. The findings showed that Shigella flexneri, Salmonella Typhimurium, and Salmonella enterica recovery were completely inhibited within 5 min. Escherichia coli and Staphylococcus aureus recovery were completely inhibited at 10 and 30 min, respectively. The ZIB test showed that 5% CO had the highest inhibitory effect on both Salmonella strains and E. coli with approximately 10 mm ZIB diameter. Additionally, 5% CO completely inactivated all bacterial strains on spinach samples and in the wash water except for S. aureus. A total of 80 mg/L peracetic acid (PAA) resulted in >2log CFU/mL recovery on experimental washed samples. These findings suggest that 5% CO was highly effective in inhibiting microbial growth on RTE spinach, potentially contributing to sustainable food safety and shelf-life extension strategies.

Microbial Contamination and Antibiotic Resistance in Fresh Produce and Agro-Ecosystems in South Asia-A Systematic Review

Fresh produce prone to microbial contamination is a potential reservoir for antimicrobial-resistant bacteria (ARB) and antimicrobial resistance genes (ARGs), posing challenges to food safety and public health. This systematic review aims to comprehensively assess the prevalence of bacterial pathogens and the incidence of ARB/ARGs in fresh produce and agro-ecosystems across South Asia. Twenty-two relevant studies published between 2012 and 2022 from three major scientific databases and the grey literature were identified. The results revealed a wide occurrence of microbial contamination in various types of fresh produce across South Asia, with a predominance of E. coli (16/22), Salmonella spp. (13/22), Staphylococcus spp. (5/22), and Klebsiella spp. (4/22). The agro-ecosystem serves as a complex interface for microbial interactions; studies have reported the prevalence of E. coli (1/4), Salmonella spp. (1/4) and Listeria monocytogenes (1/4) in farm environment samples. A concerning prevalence of ARB has been reported, with resistance to multiple classes of antibiotics. The presence of ARGs in fresh produce underscores the potential for gene transfer and the emergence of resistant pathogens. To conclude, our review provides insights into the requirements of enhanced surveillance, collaborative efforts, implementation of good agricultural practices, and public awareness for food safety and safeguarding public health in the region.

Understanding the potential of fresh produce as vehicles of Salmonella enterica

This chapter presents an overview of Salmonella enterica as a contaminant in fresh produce, exploring outbreaks and recalls linked to them. It also provides information on potential sources of S. enterica contamination throughout the entire production chain of these products and presents food safety tools and new approaches for controlling this pathogen. S. enterica is recognized worldwide as a pathogen responsible for foodborne outbreaks, and there has been an increase in reported cases of salmonellosis linked to fresh produce. These products are susceptible to contamination throughout various stages of the farm-to-fork process. The potential sources of contamination are present from pre-harvest and harvest stages (e.g., soil, blossoms, seeds, irrigation water and gray/blackwater, wild and domestic animals/organic fertilizers, and distinctive traits of the plant) to post-harvest stages (e.g., processing, packaging, storage/retail, and preparing for consumption). Thus, controlling S. enterica contamination is extremely important for ensuring the safe consumption of fresh produce. However, obtaining practical, efficient, low-cost, and sustainable solutions that ensure the products' sensorial, nutritional, and food quality is still a challenge. As an alternative to conventional methods, recent studies report the use of new technologies, such as neutral, acidic or low chlorine electrolyzed oxidizing water, ultraviolet light, ultrasound, microemulsion of essential oils, cold plasma, irradiation, bacteriophages, and other methods, which can be used alone or in combination with the conventional ones. Therefore, understanding the main sources of S. enterica contamination in fresh produce and the effective approach for controlling this pathogen is crucial to reducing future outbreaks.

Investigating processing practices and microbiological quality of minimally processed vegetables in Brazil

Minimally processed vegetables (MPVs) are marketed as convenient and healthy choices for consumers. However, the absence of post-commercialization treatments raises concerns about their microbiological safety. This study investigated the processing practices of 28 Brazilian MPV plants and compared the microbiological quality of these products with fresh counterparts in the city of Sao Paulo, Brazil. Through cluster analysis, the processing plants were categorized into two groups: group 1 (nineteen plants) primarily uses chemical substances in the washing step, while group 2 (nine plants) avoids chemical use but employs similar rinsing practices. Microbiological analysis of 100 samples (49 unprocessed and 51 MPVs) revealed no significant differences in microbial group counts (Enterobacteriaceae, coliforms, and E. coli) between the in natura (unprocessed) and MPV products. However, the prevalence of E. coli was higher in natura vegetables than in MPVs. The results indicated the presence of Salmonella DNA (from either dead or live cells or residual DNA) in 4 samples (3 in natura and 1 MPV) using conventional PCR, suggesting the presence of the pathogen in these samples. Listeria monocytogenes was absent, but Listeria innocua was found in two unprocessed products. The study suggests that certain MPVs have microbial loads similar to unprocessed vegetables, potentially serving as carriers for pathogen transmission. These findings emphasize the importance of understanding practices in Brazilian MPV processing plants, informing the implementation of control measures to improve MPV safety and shelf-life, thus ensuring microbiological safety.

Carvacrol and thymol effect in vapor phase on Escherichia coli and Salmonella serovar Typhimurium growth inoculated in a fresh salad

This study aimed to evaluate the antimicrobial effect of thymol and carvacrol in inhibiting Escherichia coli and Salmonella serovar Typhimurium inoculated on a fresh green salad through the vapor phase. A film-forming solution was prepared by dissolving starch, sorbitol, and variying concentrations of carvacrol, thymol, and a mixture of both. The film-forming solution containing the respective antimicrobial agent was then added lid, which was sealed rigidly and hermetically to achieve different concentrations (105 mg/L of air of carvacrol, 105 mg/L of air of thymol, and a mixture of 52 mg/L of air of carvacrol and 52 mg/L of air of thymol). Each active package contained fresh green salad inoculated with E. coli or Salmonella serovar Typhimurium. The active packages were then sealed and refrigerated at a temperature of 6 °C for 48 h. Growth/inhibition curves were modelled using the Weibull equation, and consumer acceptance was evaluated. Carvacrol can reduce up to 0.5 log-cycles, while thymol can reach almost 1 log cycle. Blending the components with half the concentration has a synergistic effect, inhibiting up to 2.5 log cycles. Consumer ratings revealed no significant differences between the packages. However, the average score was 5.4 on a 9-point hedonic scale, evaluators' comments did not indicate dislike or a strong taste characteristic of thymol and carvacrol.

Pulsed-control plasma-activated water: An emerging technology to assist ultrasound for fresh-cut produce washing

In this study, we explored the use of plasma-activated water (PAW) in combination with ultrasound (US) for food disinfection. Our research introduces a novel approach that utilizes a pulsed-control (PC) method to modify the PAW. The resulting PCPAW exhibits significantly higher concentrations of key reactive oxygen and nitrogen species (RONS) compared to conventional PAW. The disinfection efficacy of US-PCPAW against fresh-cut lettuce was compared to that of US-PAW, US, and PCPAW. The combination of US and PCPAW was highly effective in reducing food-borne pathogens, surpassing single treatments in count reduction and minimizing cross-contamination. Furthermore, our study demonstrates that US-PCPAW effectively controls browning appearance without compromising sensory attributes. These findings suggest that PCPAW, as a novel disinfectant, can be a valuable addition to US to enhance the quality and safety of fresh-cut produce.

Unveiling Fresh-Cut Lettuce Processing in Argentine Industries: Evaluating Salmonella Levels Using Predictive Microbiology Models

A survey was performed to gather information on the processing steps, conditions, and practices employed by industries processing ready-to-eat (RTE) leafy vegetables in Argentina. A total of seven industries participated in the survey. A cluster analysis of the data obtained was performed to identify homogeneous groups among the participating industries. The data collected were used as inputs of two predictive microbiology models to estimate Salmonella concentrations after chlorine washing, during storage and distribution of final products, and to rank the different practices according to the final estimated Salmonella levels. Six different clusters were identified by evaluating the parameters, methods, and controls applied in each processing step, evidencing a great variability among industries. The disinfectant agent applied by all participating industries was sodium hypochlorite, though concentrations and application times differed among industries from 50 to 200 ppm for 30 to 110 s. Simulations using predictive models indicated that the reductions in Salmonella in RTE leafy vegetables would vary in the range of 1.70-2.95 log CFU/g during chlorine-washing depending on chlorine concentrations applied, washing times, and vegetable cutting size, which varied from 9 to 16 cm2 among industries. Moreover, Salmonella would be able to grow in RTE leafy vegetables during storage and distribution, achieving levels of up to 2 log CFU/g, considering the storage and transportation temperatures and times reported by the industries, which vary from 4 to 14 °C and from 18 to 30 h. These results could be used to prioritize risk-based sampling programs by Food Official Control or determine more adequate process parameters to mitigate Salmonella in RTE leafy vegetables. Additionally, the information gathered in this study is useful for microbiological risk assessments.

A New Ready-to-Eat Product Based on Enzymatically Peeled 'Hernandina' Clementine Segments and Citrus Syrup

Ready-to-eat fresh fruit have an increasing presence in international markets due to their convenience and health benefits. However, these products are highly perishable and efficient technologies to increase their shelf life are needed. In the present research, different citrus fruit species and cultivars from organic farming were assessed to obtain enzymatically peeled citrus segments. The best results in terms of segment quality were observed for 'Hernandina' clementine, which was chosen to make a new ready-to-eat product based on peeled citrus segments that were packaged in glass jars with a light syrup made of citrus juice and organic sugar cane. Different citrus juice mixtures were assayed and the most appreciated syrup, based on the sensory scores given by panellists, was that containing 50-50 (v/v) of 'Fino' lemon and 'Hernandina' clementine juices. In addition, different pasteurization treatments were assessed for their effects on conserving the safety, nutritional quality and sensory properties of the product during cold storage. The results show that pasteurization treatment at 50 °C for 45 min was sufficient to prevent microbial contamination with mesophilic and psychrophilic aerobic bacteria or yeast and mould and to maintain sensory properties until five weeks of storage at 4 °C. In addition, only a 10% reduction in vitamin C concentrations was observed in fresh-segments or syrup until the end of the storage period, showing that a high bioactive compound content and health benefits were conserved in the new ready-to-eat product after pasteurization and prolonged cold storage.

Effect of cold atmospheric plasma torch distance on the microbial inactivation and sensorial properties of ready-to-eat olivier salad

This study aimed to investigate the effect of the cold atmospheric plasma torch (CAPT) nozzle distance from the surface of Olivier salad and the treatment time in the reduction of microbial load and sensory properties of the product simultaneously. In this study, the CAPT nozzle was placed at 3, 5, and 7 cm distances from the surface of the Olivier salad, and its efficiency in inactivating the microbial population, decimal reduction time (D-value), and sensory evaluation of the product were evaluated. The results showed that reducing the distance and increasing the plasma treatment time (30, 60, 90, and 120 s) both reduced the microbial load of the product. The maximum inactivation and the minimum D-value are related to the 3 cm distance for 120 s, which has been 3.77, 2.91, and 1.52 log CFU/g for Coliform, Total viable count (TVC), mold and yeast, respectively. The lowest D-value was related to Coliform (4.41 s). CAPT treatment had no significant sensible effect on the product's sensory characteristics compared to the control sample. The treated sample at a 3 cm distance for 90 s and the microbial reduction to an acceptable amount and high acceptancy from sensory evaluators were selected as the superior treatment in this study. Also, the results showed that CAPT could be used successfully in ready-to-eat (RTE) products.

Minimally Processed Vegetables in Brazil: An Overview of Marketing, Processing, and Microbiological Aspects

The global demand for minimally processed vegetables (MPVs) has grown, driven by changes in the population's lifestyle. MPVs are fresh vegetables that undergo several processing steps, resulting in ready-to-eat products, providing convenience for consumers and food companies. Among the processing steps, washing-disinfection plays an important role in reducing the microbial load and eliminating pathogens that may be present. However, poor hygiene practices can jeopardize the microbiological quality and safety of these products, thereby posing potential risks to consumer health. This study provides an overview of minimally processed vegetables (MPVs), with a specific focus on the Brazilian market. It includes information on the pricing of fresh vegetables and MPVs, as well as an examination of the various processing steps involved, and the microbiological aspects associated with MPVs. Data on the occurrence of hygiene indicators and pathogenic microorganisms in these products are presented. The focus of most studies has been on the detection of Escherichia coli, Salmonella spp., and Listeria monocytogenes, with prevalence rates ranging from 0.7% to 100%, 0.6% to 26.7%, and 0.2% to 33.3%, respectively. Foodborne outbreaks associated with the consumption of fresh vegetables in Brazil between 2000 and 2021 were also addressed. Although there is no information about whether these vegetables were consumed as fresh vegetables or MPVs, these data highlight the need for control measures to guarantee products with quality and safety to consumers.

Carvacrol-loaded nanoemulsions produced with a natural emulsifier for lettuce sanitization

Carvacrol is an antimicrobial agent that shows potential for eliminating microorganisms in vegetables, increasing food safety. However, intense odor and low water solubility of carvacrol are limiting factors for its application for fresh vegetables sanitization, which can be overcome by nanotechnology. Two different nanoemulsions containing carvacrol (11 mg/mL) were developed by probe sonication: carvacrol-saponin nanoemulsion (CNS) and carvacrol-polysorbate 80 nanoemulsion (CNP). Formulations presented appropriate droplet sizes (from 74.7 nm to 168.2 nm) and high carvacrol encapsulation efficiency (EE) (from 89.5 % to 91.5 %). CNS showed adequate droplet size distribution (PDI < 0.22) and high zeta potential values (around -30 mV) compared to CNP, with saponin chosen for the following experiments. Carvacrol nanoemulsions presented Bacterial Inactivation Concentration (BIC) against the Salmonella cocktail from 5.51 to 0.69 mg/mL and for the E. coli cocktail from 1.84 to 0.69 mg/mL. Among all tested nanoemulsions, CNS1 presented the lowest BIC (0.69 mg/mL) against both bacterial cocktails. Damage to bacterial cells in lettuce treated with nanoemulsion was confirmed by scanning electron microscopy. For lettuce sanitization, CNS1 showed a similar effect to unencapsulated carvacrol, with a high bacterial reduction (>3 log CFU/g) after lettuce immersion for 15 min at 2 × BIC. Using the same immersion time, the CNS1 (2 × BIC) demonstrated equal or better efficacy in reducing both tested bacterial cocktails (>3 log CFU/g) when compared to acetic acid (6.25 mg/mL), citric acid (25 mg/mL), and sodium hypochlorite solution (150 ppm). Lettuce immersed in CNS1 at both concentrations (BIC and 2 × BIC) did not change the color and texture of leaves, while the unencapsulated carvacrol at 2 × BIC darkened them and reduced their firmness. Consequently, carvacrol-saponin nanoemulsion (CNS1) proved to be a potential sanitizer for lettuce.

Effects of chlorine and peroxyacetic acid wash treatments on growth kinetics of Salmonella in fresh-cut lettuce

Fresh-cut produces are often consumed uncooked, thus proper sanitation is essential for preventing cross contamination. The reduction and subsequent growth of Salmonella enterica sv Thompson were studied in pre-cut iceberg lettuce washed with simulated wash water (SWW), sodium hypochlorite (SH, free chlorine 25 mg/L), and peroxyacetic acid (PAA, 80 mg/L) and stored for 9 days under modified atmosphere at 9, 13, and 18 °C. Differences in reduction between SH and PAA were non-existent. Overall, visual quality, dehydration, leaf edge and superficial browning and aroma during storage at 9 °C were similar among treatments, but negative effects increased with temperature. These results demonstrated that PAA can be used as an effective alternative to chlorine for the disinfection of Salmonella spp. in fresh-cut lettuce. The growth of Salmonella enterica sv Thompson was successfully described with the Baranyi and Roberts growth model in the studied storage temperature range, and after treatment with SWW, chlorine, and PAA. Subsequently, predictive secondary models were used to describe the relationship between growth rates and temperature based on the models' family described by Bělehrádek. Interestingly, the exposure to disinfectants biased growth kinetics of Salmonella during storage. Below 12 °C, growth rates in lettuce treated with disinfectant (0.010-0.011 log CFU/h at 9 °C) were lower than those in lettuce washed with water (0.016 log CFU/h at 9 °C); whereas at higher temperatures, the effect was the opposite. Thus, in this case, the growth rate values registered at 18 °C for lettuce treated with disinfectant were 0.048-0.054 log CFU/h compared to a value of 0.038 log CFU/h for lettuce treated with only water. The data and models developed in this study will be crucial to describing the wash-related dynamics of Salmonella in a risk assessment framework applied to fresh-cut produce, providing more complete and accurate risk estimates.

Concentration-dependent effect of eugenol on porcine myofibrillar protein gel formation

The effects of different concentrations of eugenol (EG = 0, 5, 10, 20, 50, and 100 mg/g protein) on the structural properties and gelling behavior of myofibrillar proteins (MPs) were investigated. The interaction of EG and MPs decreased free thiol and amine content, and reduced tryptophan fluorescence intensity and thermal stability, but enhanced surface hydrophobicity and aggregation of MPs. Compared with the control (EG free), the MPs' gels treated with 5 and 10 mg/g of EG had a higher storage modulus, compressive strength, and less cooking loss. A high microscopic density was observed in these EG-treated gels. However, EG at 100 mg/g was detrimental to the gelling properties of the MPs. The results indicate that an EG concentration of 20 mg/g is a turning point, i.e., below 20 mg/g, EG promoted MPs gelation, but above 20 mg/g, it impeded gelation by interfering with protein network formation. The EG modification of MPs could provide a novel ingredient strategy to improve the texture of comminuted meat products.

Heavy metal, microbial and pesticides residue contaminations are limiting the potential consumption of green leafy vegetables in Ghana: An overview

Green leafy vegetables (such as cocoyam (Colocasia spp) leaves, spinach (Spinach spp), amaranths (Amaranthus spp), roselle leaves (Hibiscus spp), and lettuce (Lactuca spp)) form a major part of Ghanaian meals providing essential vitamin such as A, B and C and minerals including iron and calcium as well as essential bioactive compounds. However, the practices involved in the production, distribution and handling of these nutrient rich vegetables, by most value chain actors in Ghana, unfortunately pre-dispose them to contamination with pathogens, heavy metals and pesticides residues. These have therefore raised public health concerns regarding the safety and quality of these green leafy vegetables. Understanding the current perspectives of the type of pathogens, heavy metals and pesticide contaminants that are found in leafy vegetables and their health impacts on consumers will go a long way in helping to identify appropriate mitigation measures that could be used to improve the practices involved and thereby help safeguard human health. This review examined reported cases of microbial, heavy metal and pesticides residue contamination of green leafy vegetables in Ghana from 2005 to 2022. Notable pathogenic microorganisms were Ascaris eggs and larvae, faecal coliform, Salmonella spp., Staphylococcus aureus Streptococci, Clostridium perfringes, and Escherichia coli. In addition, Lead (Pb), Cadmium (Cr), Chromium (Cr), Zinc (Zn), Iron (Fe), Copper (Cu) and Manganese (Mn) have been detected in green leafy vegetables over the years in most Ghanaian cities. Pesticides residues from organochlorine, organophosphorus and synthetic pyrethroid have also been reported. Overall, microbial, heavy metals and pesticide residue contamination of Ghanaian green leafy vegetables on the farms and markets were significant. Hence, mitigation measures to curb the contamination of these vegetables, through the food chain, is urgently required to safeguard public health.

Foliar Roughness and Water Content Impact on Escherichia coli Attachment in Baby Leafy Greens

Understanding the relation between the susceptibility of different leafy greens to human pathogen contamination and leaf traits can contribute to increase the food safety of the fresh vegetable industry. The aim of this research was to evaluate the susceptibility to E. coli ATCC 35218 attachment in 30 accessions of baby leaves, and to identify leaf traits potentially involved in the contamination. The accessions were surface inoculated with a bacterial suspension containing 1 × 10⁷ cells/mL and the attachment was measured 1.5 h after inoculation. Significant differences in attachment were detected between the accessions for p ≤ 0.05. The three most and the three least susceptible accessions were selected and characterized for leaf micro-morphological traits (stomata density and size, surface roughness) and water content. Scanning electron microscopy was used to analyse the stomatal parameters. Roughness was measured by an innovative portable 3D digital microscope. No significant correlation between the attachment of E. coli ATCC 35218 and stomatal parameters was detected, while the attachment was positively correlated with roughness and water content. The E. coli ATCC 35218 population in surface-inoculated leaves was also measured after a UV treatment, which was found to be less effective in reducing bacterial contamination in the rougher leaves. This result suggested that roughness offers UV protection, further highlighting its impact on the microbiological safety of baby leafy greens.

Biostimulant Formulations and Moringa oleifera Extracts to Improve Yield, Quality, and Storability of Hydroponic Lettuce

The urgent need to increase the sustainability of crop production has pushed the agricultural sector towards the use of biostimulants based on natural products. The current work aimed to determine whether the preharvest application of two commercial formulations, based on a Fabaceae enzymatic hydrolysate or a blend of nitrogen sources including fulvic acids, and two lab-made aqueous extracts from Moringa oleifera leaves (MLEs), could improve yield, quality, and storability of lettuce grown in a hydroponic system, as compared to an untreated control. Lettuce plants treated with the MLEs showed significantly improved quality parameters (leaf number, area, and color), total phenolic content and antioxidant activity, and resistance against the fungal pathogen Botrytis cinerea, comparable to that obtained with commercial formulates, particularly those based on the protein hydrolysate. A difference between the M. oleifera extracts was observed, probably due to the different compositions. Although further large-scale trials are needed, the tested MLEs seem a promising safe and effective preharvest means to improve lettuce agronomic and quality parameters and decrease susceptibility to rots.

Metagenomic-based surveillance systems for antibiotic resistance in non-clinical settings

The success of antibiotics as a therapeutic agent has led to their ineffectiveness. The continuous use and misuse in clinical and non-clinical areas have led to the emergence and spread of antibiotic-resistant bacteria and its genetic determinants. This is a multi-dimensional problem that has now become a global health crisis. Antibiotic resistance research has primarily focused on the clinical healthcare sectors while overlooking the non-clinical sectors. The increasing antibiotic usage in the environment - including animals, plants, soil, and water - are drivers of antibiotic resistance and function as a transmission route for antibiotic resistant pathogens and is a source for resistance genes. These natural compartments are interconnected with each other and humans, allowing the spread of antibiotic resistance via horizontal gene transfer between commensal and pathogenic bacteria. Identifying and understanding genetic exchange within and between natural compartments can provide insight into the transmission, dissemination, and emergence mechanisms. The development of high-throughput DNA sequencing technologies has made antibiotic resistance research more accessible and feasible. In particular, the combination of metagenomics and powerful bioinformatic tools and platforms have facilitated the identification of microbial communities and has allowed access to genomic data by bypassing the need for isolating and culturing microorganisms. This review aimed to reflect on the different sequencing techniques, metagenomic approaches, and bioinformatics tools and pipelines with their respective advantages and limitations for antibiotic resistance research. These approaches can provide insight into resistance mechanisms, the microbial population, emerging pathogens, resistance genes, and their dissemination. This information can influence policies, develop preventative measures and alleviate the burden caused by antibiotic resistance.

Ultrasound, Acetic Acid, and Peracetic Acid as Alternatives Sanitizers to Chlorine Compounds for Fresh-Cut Kale Decontamination

Chlorinated compounds are usually applied in vegetable sanitization, but there are concerns about their application. Thus, this study aimed to evaluate ultrasound (50 kHz), acetic acid (1000; 2000 mg/L), and peracetic acid (20 mg/L) and their combination as alternative treatments to 200 mg/L sodium dichloroisocyanurate. The overall microbial, physicochemical, and nutritional quality of kale stored at 7 °C were assessed. The impact on Salmonella enterica Typhimurium was verified by plate-counting and scanning electron microscopy. Ultrasound combined with peracetic acid exhibited higher reductions in aerobic mesophiles, molds and yeasts, and coliforms at 35 °C (2.6; 2.4; 2.6 log CFU/g, respectively). Microbial counts remained stable during storage. The highest reduction in Salmonella occurred with the combination of ultrasound and acetic acid at 1000 mg/L and acetic acid at 2000 mg/L (2.8; 3.8 log CFU/g, respectively). No synergistic effect was observed with the combination of treatments. The cellular morphology of the pathogen altered after combinations of ultrasound and acetic acid at 2000 mg/L and peracetic acid. No changes in titratable total acidity, mass loss, vitamin C, or total phenolic compounds occurred. Alternative treatments presented equal to or greater efficacies than chlorinated compounds, so they could potentially be used for the decontamination of kale.

Microbiological quality of ready–to–eat vegetables salads served at meat restaurants under the COVID-19 in Turkey

In Turkish cuisine, ready–to–eat vegetable salads (REVS) served with pide/lahmacun, kebab types, and tantuni from animal source in meat restaurants were evaluated since they have the potential to carry risks in terms of Public Health. The microbiological properties of REVS were investigated using agar plate method. Antimicrobial resistance of foodborne pathogens including Escherichia coli and Staphylococcus aureus was tested using Kirby–Bauer disc diffusion method. Moreover, the presence of important enteric viruses was detected by Polymerase Chain Reaction (PCR). The number of total aerobic bacteria, coliform bacteria, yeast and molds and, Staphylococcus and Micrococcus spp. ranged from less than 1 to 6.40, 1 to 6.26, less than 1–5.82 and less than 1–5.66 log10 colony forming units·grams-1 (CFU·g–1) in REVS samples, respectively. None of the REVS tested in this study contained Salmonella spp., whereas E. coli and S. aureus were isolated in 38.1% (16/42) and 2.4% (1/42), respectively. S. aureus was resistant to gentamicin, kanamycin, aztreonam, and ciprofloxacin in the disc diffusion assay, however, it was not harboring the mecA gene. E. coli strains (n=16) were resistant (100%) to aminoglycoside antibiotics and 35.7% (6/16) of the isolates were extended spectrum beta lactamase (ESBL) producing. blaTEM and blaCTXM8/25 were detected in two isolates, whereas one isolate carried blaCTXM–1 and blaTEM together by PCR. Of the REVS, two were evaluated as positive for rotavirus (4.8%), six for hepatitis A (14%), and hepatitis E virus (14%). These results indicate the high microorganism load, presence of ESBL E. coli, and viral enteric pathogens in REVS, hence it is important to perform routine hygiene practices.

Rapid detection of Salmonella enterica in leafy greens by a novel DNA microarray-based PathogenDx system

The diverse matrices pose great challenges for rapid detection of low Salmonella level (<10 CFU) in fresh produce. The applicability of microarray-based PathogenDx system for detecting low contamination of Salmonella Newport from leafy greens was evaluated. A pre-PCR preparation protocol including enrichment in universal pre-enrichment broth for 3 h followed by sample concentration using an InnovaPrep bio-concentrator or 6 h enrichment without a concentration step was used for detecting S. Newport from leafy greens with initial inoculum level at ∼6 CFU/25 g. Among 205 samples tested, 98%, 93%, 76%, and 60% of Romaine lettuce, Iceberg lettuce, kale, and spinach samples were tested positive after 3 h of enrichment with sample concentration. After 6 h of enrichment, 100%, 98%, 90%, and 82% of Romaine lettuce, Iceberg lettuce, kale, and spinach samples were positive. The samples were parallelly tested by the FDA bacterial analytical manual (BAM) method and 100% of spiked produce samples were tested positive. The overall analysis time of this methodology was between 8 and 11 h, including all pre-enrichment and concentration steps, in contrast to 4-5 days required for BAM method. The system correctly differentiated all 108 Salmonella strains and 35 non-Salmonella strains used in the study. This novel microarray approach provides a rapid method for detecting Salmonella in leafy greens.

Chlorophyllin-Based 405 nm Light Photodynamic Improved Fresh-Cut Pakchoi Quality at Postharvest and Inhibited the Formation of Biofilm

The aim of this study was to evaluate the effect of chlorophyllin-based photodynamic inactivation (Chl-PDI) on biofilm formation and fresh-cut pakchoi quality during storage. Firstly, Chl-based PDI reduced the amount of biofilm in an in vivo experiment and inactivated the food spoilage bacteria. Antibacterial mechanism analysis indicated that the bacterial extracellular polysaccharides and extracellular proteins were vulnerable targets for attacks by the Chl-based PDI. Then, the food spoilage microorganisms (Pseudomonas reinekei and Pseudomonas palleroniana) were inoculated onto the surface of fresh-cut pakchoi. We used chlorophyllin (1 × 10⁻⁵ mol/L) and 405 nm light (22.27 J/cm² per day) to investigate the effect of Chl-based PDI treatment on fresh-cut pakchoi quality during storage. The results showed that Chl-based PDI increased the visual quality and the content of chlorophyll, VC, total soluble solids, and SOD activity and decreased the occurrence of leaf yellowing and POD activity. These suggest that Chl-based PDI can be used for the preservation of fresh-cut pakchoi and has the potential to inhibit biofilm formation of food spoilage bacteria. It is of great significance for the effective processing and traditional vegetable preservation.

Evaluation of the Persistence and Characterization of Listeria monocytogenes in Foodservice Operations

Listeria monocytogenes is a major foodborne pathogen that can contaminate food products and colonize food-producing facilities. Foodservice operations (FSOp) are frequently responsible for foodborne outbreaks due to food safety practices failures. We investigated the presence of and characterized L. monocytogenes from two FSOp (cafeterias) distributing ready-to-eat meals and verified FSOp’s compliance with good manufacturing practices (GMP). Two facilities (FSOp-A and FSOp-B) were visited three times each over 5 months. We sampled foods, ingredients, and surfaces for microbiological analysis, and L. monocytogenes isolates were characterized by phylogenetic analyses and phenotypic characteristics. GMP audits were performed in the first and third visits. A ready-to-eat salad (FSOp-A) and a frozen ingredient (FSOp-B) were contaminated with L. monocytogenes, which was also detected on Zone 3 surfaces (floor, drains, and a boot cover). The phylogenetic analysis demonstrated that FSOp-B had persistent L. monocytogenes strains, but environmental isolates were not closely related to food or ingredient isolates. GMP audits showed that both operations worked under “fair” conditions, and “facilities and equipment” was the section with the least compliances. The presence of L. monocytogenes in the environment and GMP failures could promote food contamination with this pathogen, presenting a risk to consumers.

Detection and analysis of indicator and pathogenic bacteria in conventional and organic fruits and vegetables sold in retail markets

Produce-associated foodborne outbreaks have been increasingly implicated as the significant proportion of the annual incidence of foodborne illness worldwide. The objectives of this study were to determine the concentrations of indicator bacteria and the presence of Salmonella spp., Shigella spp., Escherichia coli O157:H7, and Listeria monocytogenes, and to characterize predictors associated with Salmonella contamination of retail produce from fresh markets and supermarkets in Bangkok, Thailand. A total of 503 samples were collected during May 2018 and February 2019, comprised of sweet basil, spring onion, coriander, cabbage, lettuce, cucumber, and tomato, with n = 167 conventional items from fresh open-air markets, n = 168 conventional items from supermarkets, and n = 168 organic items from supermarkets. The overall prevalence in these 503 items for fecal coliforms and E. coli were 84.3% and 71.4%, with mean concentrations (± S.D.) of fecal coliforms and E. coli being 3.0×105 (± 1.3×106) and 1.8×105 (± 1.1×105) MPN/g, respectively. The concentration of fecal coliforms and E. coli was higher in produce sampled from fresh open-air markets than produce from supermarkets; similarly, these bacterial indicators were higher from produce grown under conventional methods than certified organic produce. The prevalence of Salmonella and Shigella was 4.8% and 0.4%, respectively, but no positives were found for E. coli O157:H7 and L. monocytogenes. The predominant Salmonella serovar were Stanley (30.8%). Based on logistic regression, the odds of Salmonella contamination were significantly (p &lt; 0.05) higher during the rainy versus dry season, produce grown using conventional versus organic agriculture, sweet basil versus other commodities, and using ice tank versus dry refrigeration for overnight retail storage. This study indicated that fruits and vegetables are important sources of microbial contamination. Hence, monitoring and surveillance of pathogen contamination to produce is needed to strengthen food safety.

Microbial Quality and Safety of Raw Vegetables of Fiche Town, Oromia, Ethiopia

Vegetables contain vital ingredients such as minerals, phytochemicals, vitamins, and fibers, which play significant roles in human health. Consumption of fresh vegetables causes human infections and outbreaks while serving as a reservoir of several pathogens. The study evaluated the microbiological quality of raw vegetables consumed in and around Fiche town, Central Ethiopia. For the experimental study, a total of 100 samples of 5 different raw vegetables from two local markets were selected based on their commonalities for overall microbial quality in terms of aerobic mesophilic count, total coliform count, Enterobacteriaceae count, Staphylococci count, and yeast and mold levels. The highest count was aerobic mesophilic bacteria (5.7 log CFU/g) followed by Enterobacteriaceae (4.7 log CFU/g), while yeasts and molds count the least. The maximal count for aerobic mesophilic bacteria was enumerated in cabbage (6.4 log CFU/g) while the minimum was in green pepper samples (4.7 log CFU/g). Among 100 vegetable samples analyzed, 11% were contaminated by S. aureus which is highly prevalent in cabbage (20%), followed by lettuce (15%). In the present study, 15.0% of vegetable samples were positive for Salmonella and detected in all vegetable types.

Assessment of the Microbiological Quality of Ready-to-Eat Salads-Are There Any Reasons for Concern about Public Health?

Ready-to-eat food products can be readily consumed without further preparation and are convenient for busy on-the-go consumers. The objective of the study was to assess the microbiological quality of ready-to-eat salads. Thirty RTE salads were tested for the presence of bacteria, yeasts, and molds using the TEMPO and agar plate method. The study demonstrated that most of the tested products were characterized by varying microbiological quality. The total number of mesophilic microbiotas was about 6 log CFU g^-1. The high number of microorganisms was due to yeast and molds or Enterobacteriaceae. Half of the salads were contaminated with E. coli and three salads were contaminated with S. aureus. LAB were also found, which can be explained mainly by a dairy ingredient. In some salads, Salmonella spp. and L. monocytogenes were detected (26.7% and 33.3% of the samples, respectively). Based on the conducted tests, it was found that the microbiological quality was not satisfactory. The results presented in this study indicate that there is a significant problem of the presence of pathogens. Manufacturers should strive to reduce the possibility of microbial contamination through the use of widely understood hygiene of the production process, using hurdle technology, including the modified atmosphere and refrigerated storage.

Chitosan with pendant (E)-5-((4-acetylphenyl) diazenyl)-6-aminouracil groups as synergetic antimicrobial agents

Conventional antimicrobial agents are losing the war against drug resistance day-by-day. Chitosan biopolymer is one of the alternative materials that lends itself well to this application by fine-tuning its bioactivity...

Influence of Ecklonia maxima Extracts on Growth, Yield, and Postharvest Quality of Hydroponic Leaf Lettuce

Ecklonia maxima is a brown algae seaweed largely harvested over the last years and used to produce alginate, animal feed, fertilizers, and plant biostimulants. Their extracts are commercially available in various forms and have been applied to many crops for their growth-promoting effects which may vary according to the treated species and doses applied. The aim of the study was to characterize the effect of adding an Ecklonia maxima commercial extract (Basfoliar Kelp; 0, 1, 2, and 4 mL L−1) to the nutrient solution of a hydroponic floating system on growth, yield, and quality of leaf lettuce at harvest and during cold storage (21 days at 4 °C). The supplementation of the E. maxima extract through the mineral nutrient solutions, especially between 2 and 4 mL L−1, enhanced plant growth and improved the yield and many morphological and physiological traits (biomass accumulation, leaf expansion, stomatal conductance, water use efficiency, nitrogen use efficiency, etc.). Preharvest treatments with E. maxima extract were effective in delaying leaf senescence and extending the shelf-life of fresh-cut leaf lettuce. The delay in leaf decay of treated samples allowed to retain an overall quality over the threshold of marketability for up to 21 d of cold storage, especially using 2 mL L−1 of extract.

Isolation and Characterization of a Virulent Bacteriophage for Controlling Salmonella Enteritidis Growth in Ready-to-Eat Mixed-Ingredient Salads

ABSTRACT

Ready-to-eat vegetable salads have gained popularity worldwide. However, the microbial safety of these salads is a health concern, primarily due to Salmonella Enteritidis contamination during the growing, harvesting, processing, and handling of produce. In this study, a bacteriophage-based strategy was developed to control Salmonella Enteritidis growth in mixed-ingredient salads. The lytic Salmonella-specific phage SapYZU01 was isolated from a soil sample from a suburban vegetable field in Yangzhou (People's Republic of China). SapYZU01 has a short latent period, a large burst size, and a lytic effect against 13 Salmonella Enteritidis strains isolated from various sources (human samples, pork, deli foods, chickens, and chicken meat). The SapYZU01 genome did not contain virulence or antibiotic resistance genes. SapYZU01 significantly decreased the viability of Salmonella Enteritidis cells in iceberg lettuce, chicken meat, and mixed-ingredient (lettuce plus chicken) salads at 37 and 25°C. Bacterial levels in the salad decreased significantly (by 4.0 log CFU/g) at 25°C after treatment of contaminated lettuce before salad preparation with SapYZU01 at a multiplicity of infection (MOI) of 100. Bacterial levels were decreased by 3.8 log CFU/g at 25°C in lettuce plus chicken salads treated after the salad preparation with SapYZU01 at an MOI of 100. In contrast, treating cooked chicken meat with SapYZU01 at an MOI of 100 before mixing it with contaminated lettuce decreased the bacterial level of the salad by 1.2 log CFU/g at 25°C. These findings indicate the potential application of SapYZU01 as a natural biocontrol agent against Salmonella Enteritidis in mixed-ingredient salads. However, both the treatment method and the bacteriophage MOI must be considered when using this lytic bacteriophage in mixed-ingredient salads.

HIGHLIGHTS

NGS Techniques Reveal a High Diversity of RNA Viral Pathogens and Papillomaviruses in Fresh Produce and Irrigation Water

Fresh fruits and vegetables are susceptible to microbial contamination at every stage of the food production chain, and as a potential source of pathogens, irrigation water quality is a critical factor. Next-generation sequencing (NGS) techniques have been flourishing and expanding to a wide variety of fields. However, their application in food safety remains insufficiently explored, and their sensitivity requires improvement. In this study, quantitative polymerase chain reaction (qPCR) assays showed low but frequent contamination of common circulating viral pathogens, which were found in 46.9% of samples of fresh produce: 6/12 lettuce samples, 4/12 strawberries samples, and 5/8 parsley samples. Furthermore, the application of two different NGS approaches, target enrichment sequencing (TES) for detecting viruses that infect vertebrates and amplicon deep sequencing (ADS), revealed a high diversity of viral pathogens, especially Norovirus (NoV) and Human Papillomavirus (HPV), in fresh produce and irrigation water. All NoV and HPV types found in fresh fruit and vegetable samples were also detected in irrigation water sources, indicating that these viruses are common circulating pathogens in the population and that irrigation water may be the most probable source of viral pathogens in food samples.

Combination of ozone and ultrasonic-assisted aerosolization sanitizer as a sanitizing process to disinfect fresh-cut lettuce

Reduction of sanitizer dosage and development of non-immersion disinfection methods have become major focuses of research. Here, we examined the disinfection efficacy of combining gaseous ozone (4 and 8 ppm) with aerosolized oxidizing sanitizer [sodium hypochlorite (SH, 100 and 200 ppm)] and aerosolized organic acid [acetic acid (AA, 1% and 2%) and lactic acid (LA, 1% and 2%)]. Notably, 1% AA and 4 ppm gaseous ozone were ineffective for disinfecting Salmonella Typhimurium, and treatment with 1% AA + 8 ppm ozone caused browning of lettuce leaves and stimulated increases in aerobic mesophilic count (AMC), aerobic psychrotrophic count (APC), S. Typhimurium, and Escherichia coli O157:H7. Treatment with 2% LA + 8 ppm ozone resulted in the lowest S. Typhimurium, E. coli O157:H7, Listeria monocytogenes, AMC, APC, and molds and yeasts during storage (0-7 days at 4 °C). Quality analysis indicates that LA + 8 ppm ozone and SH + 8 ppm ozone did not negatively affect L*, a*, b*, polyphenolic content, weight loss, and sensory properties; however, the levels of two individual phenolic compounds (3,4-dihydroxybenzoic acid and vanillin), responsible for phenylpropanoid synthesis, were significantly increased after treatment with 2% LA + 8 ppm ozone. These findings provided insights into the use of LA combined with gaseous ozone for application in disinfecting fresh produce.

High prevalence of multidrug resistant Escherichia coli isolated from fresh vegetables sold by selected formal and informal traders in the most densely populated Province of South Africa

Contaminated fresh produce has increasingly been implicated in foodborne disease outbreaks. As microbiological safety surveillance in South Africa is limited, a total of 545 vegetable samples (spinach, tomato, lettuce, cucumber, and green beans) were purchased from retailers, street traders, trolley vendors and farmers' markets. Escherichia coli, coliforms and Enterobacteriaceae were enumerated and the prevalence of Escherichia coli, Salmonella spp. and Listeria monocytogenes determined. E. coli isolates were characterized phenotypically (antibiotic resistance) and genotypically (diarrheagenic virulence genes). Coliforms, E. coli and Enterobacteriaceae counts were mostly not significantly different between formal and informal markets, with exceptions noted on occasion. When compared to international standards, 90% to 98% tomatoes, 70% to 94% spinach, 82% cucumbers, 93% lettuce, and 80% green bean samples, had satisfactory (≤ 100 CFU/g) E. coli counts. Of the 545 vegetable samples analyzed, 14.86% (n = 81) harbored E. coli, predominantly from leafy green vegetables. Virulence genes (lt, st, bfpA, eagg, eaeA, stx1, stx2, and ipaH) were not detected in the E. coli isolates (n = 67) characterized, however 40.30% were multidrug-resistant. Resistance to aminoglycosides (neomycin, 73.13%; gentamycin, < 10%), penicillins (ampicillin, 38.81%; amoxicillin, 41.79%; augmentin, < 10%), sulfonamides (cotrimoxazole, 22.39%), tetracycline (19.4%), chloramphenicol (11.94%), cephalosporins (cefepime, 34.33%), and carbapenemases (imipenem, < 10%) were observed. This study highlights the need for continued surveillance of multidrug resistant foodborne pathogens in fresh produce retailed formally and informally for potential consumer health risks. PRACTICAL APPLICATION: The results indicate that the microbiological quality of different vegetables were similar per product type, regardless of being purchased from formal retailers or informal street traders, trolley vendors or farmers' markets. Although no pathogenic bacteria (diarrheagenic E. coli, Salmonella spp. or L. monocytogenes) were isolated, high levels of multidrug-resistance was observed in the generic E. coli isolates. These findings highlight the importance of microbiological quality surveillance of fresh produce in formal and informal markets, as these products can be a reservoir of multidrug resistant bacteria harboring antibiotic resistance and virulence genes, potentially impacting human health.

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.

Evaluation of Chemical and Microbiological Contaminants in Fresh Fruits and Vegetables from Peasant Markets in Cundinamarca, Colombia

ABSTRACT

In this study, chemical and microbiological contaminants were detected in fresh fruits and vegetables in peasant markets in the Department of Cundinamarca to assess food safety. At least one pesticide was detected in 63% of the samples evaluated (n = 100, including fruits and vegetables), and in 41% of these, pesticides exceeded the maximum residue limit. Within the pesticides found, 60% do not use a registry from the Instituto Colombiano Agropecuario to be applied on the crops where they were detected and are included in the toxicological categories "highly toxic" (category IB) and "moderately toxic" (category II). Heavy metals were found in 45% of the samples, with cadmium (38%) and lead (14%) being the most frequent. The pathogenic microorganisms Escherichia coli O157:H7, Listeria monocytogenes, Salmonella, and Campylobacter sp. were detected in 4, 2, 1, and 0% of the samples, respectively. Factors concerning integrated crop management, contaminated inputs with chemicals and microorganisms, and the lack of hygiene in the postharvest stage favor the presence of pesticide residues, heavy metals, and the appearance of pathogenic microorganisms. The results suggest the need to strengthen the implementation of integrated management strategies that guarantee the safety of fresh fruits and vegetables in the country.

HIGHLIGHTS

Microbiological safety of ready-to-eat minimally processed vegetables in Brazil: an overview

The market of ready-to-eat minimally processed vegetables (RTE-MPV) is increasing in Brazil and many other countries. During processing, these vegetables go through several steps that modify their natural structure while maintaining the same nutritional and sensory attributes as the fresh produce. One of the most important steps is washing-disinfection, which aims to reduce the microbial load, prevent cross-contamination and inactivate pathogenic microorganisms that may be present. Nonetheless, the presence of pathogens and occurrence of foodborne illnesses associated with consumption of RTE-MPV concern consumers, governments and the food industry. This review brings an overview on the microbiological safety of RTE-MPV, focusing on Brazilian findings. Most of the published data are on detection of Salmonella spp. and Listeria monocytogenes, indicating that their prevalence may range from 0.4% to 12.5% and from 0.6% to 3.1%, respectively. The presence of these pathogens in fresh produce is unacceptable and risky, mainly in RTE-MPV, because consumers expect them to be clean and sanitized and consequently safe for consumption without any additional care. Therefore, proper control during the production of RTE-MPV is mandatory to guarantee products with quality and safety to consumers. © 2020 Society of Chemical Industry.

Growth Potential of Listeria monocytogenes on Refrigerated Spinach and Rocket Leaves in Modified Atmosphere Packaging

Minimally processed ready-to-eat (RTE) vegetables are increasingly consumed for their health benefits. However, they also pose a risk of being ingested with food-borne pathogens. The present study investigated the ability of RTE spinach and rocket to support the growth of Listeria monocytogenes as previous studies provided contradicting evidence. Findings were compared to growth on iceberg lettuce that has repeatedly been shown to support growth. Products were inoculated with a three-strain mix of L. monocytogenes at 10 and 100 cfu g⁻¹ and stored in modified atmosphere (4 kPa O₂, 8 kPa CO₂) at 8 °C over 7–9 days. Spinach demonstrated the highest growth potential rate of 2 to 3 log₁₀ cfu g⁻¹ over a 9-day period with only marginal deterioration in its visual appearance. Growth potential on rocket was around 2 log₁₀ cfu g⁻¹ over 9 days with considerable deterioration in visual appearance. Growth potential of iceberg lettuce was similar to that of rocket over a 7-day period. Growth curves fitted closely to a linear growth model, indicating none to limited restrictions of growth over the duration of storage. The high growth potentials of L. monocytogenes on spinach alongside the limited visual deterioration highlight the potential risks of consuming this raw RTE food product when contaminated.

Detection of E. coli O157:H7 in Food Using Automated Immunomagnetic Separation Combined with Real-Time PCR

In this study, we describe the development of an automated immunomagnetic separation device combined with real-time polymerase chain reaction (PCR) for detecting foodborne bacteria. Immunomagnetic separation (IMS) is a well-known method for the separation and concentration of target bacteria from a large volume of food samples. Magnetic beads functionalized with an antibody provide selectivity for target bacteria such as Escherichia coli O157:H7. Moreover, compared to conventional methods, real-time PCR enables high-sensitivity detection of target bacteria. The method proposed in this study involves three steps: (1) pre-enrichment, (2) automated IMS and concentration of target bacteria, and (3) detection of target bacteria by real-time PCR. Using food samples with a working sample volume as large as 250 mL, the whole process only requires 3 h. As a result, target bacteria in the range of 101–102 colony-forming units per mg or g of sample can be detected in food samples, such as milk, ground beef, and cabbage, by using the proposed approach. We anticipate that the automated IMS system combined with real-time PCR will contribute to the development of a fully automated system for detecting foodborne bacteria and serve as a multi-tester for a variety of bacterial strains in the capacity of a sample-to-answer device in the near future.

Microbial Contamination, an Increasing Threat to the Consumption of Fresh Fruits and Vegetables in Today's World

Microbes are found all over the globe with some few exceptions, including sterilized surfaces. They include normal flora that is nonpathogenic, which contribute to the larger percentage, and pathogenic species which are few. Hence, the activities of humans cannot be completely separated from microbes. Thus, many pathogenic microbes have found their way into fresh fruits and vegetables which are a great source of a healthy diet for humans. The growing demand for fresh fruits and vegetables has necessitated larger production. The larger production of vegetables within the shortest possible time to meet the growing demand has placed them at a higher risk of contamination with the pathogenic microbes, making the safety of consumers uncertain. Study of sources of contamination and type of pathogenic etiological agents isolated from fresh fruits and vegetables includes Bacillus cereus, Campylobacter jejuni, Clostridium botulinum, E. coli O157: H7, Listeria monocytogenes, Salmonella spp., Shigella, Staphylococcus, and Vibrio cholera. Several measures have proven to be effective in controlling contamination of microbes and they include the establishment of surveillance systems to monitor the production chain and thoroughly washing vegetables with vinegar water. Saltwater and other washing techniques are effective but caution should be taken to make sure one does not use one cycle of water for washing all vegetables. The consumption of fresh fruits and vegetables is still encouraged by this review but significant measures must be taken to check the safety of these products before consumption.

Ready-to-eat vegetable salads served in Nigerian restaurants: a potential source of multidrug-resistant bacteria

AIM

Public health promotion of fruit and vegetables as healthier sources of nutrition in Nigeria has led to an increase in consumption of fruit and vegetables, particularly in the form of ready-to-eat (RTE) salads. However, the continual association of drug-resistant bacteria with fruit and vegetables creates an additional challenge for consumer safety. Hence this study was carried out to determine the prevalence of multidrug-resistant bacteria (MRB) in, and characterization of MRB isolated from, RTE salads.

METHODS AND RESULTS

RTE vegetable salad samples were randomly selected for bacterial analysis with Wei's Urn iterative randomization technique and a One Way Analysis of Variance performed with Kruskal-Wallis test. Total viable bacteria count (TVC) was performed with pour-plate technique. Bacterial colonies from Petri plates were tested for multidrug resistance with Kirby Bauer disc diffusion test and prevalence/counts of MRB, as well as multiple antibiotic resistance indices (MAR), was/were subsequently deduced. Mean prevalence of MRB in all RTE salad samples was estimated at 54·38% while mean counts of MRB were estimated at 6·83 ± 6·42 log₁₀ CFU per g. Prevalence of bacterial resistance to all antibiotics tested ranged from 5·92 to 100·00%. Mean MAR obtained for all RTE salad samples was estimated at 0·51 (recommended limit = 0·20) indicating that RTE salads were a potential source of MRB, with significant health risk. MRB isolated from RTE salads included Proteus vulgaris strain ATU 243, Bacillus thuringiensis strain AND 236, Citrobacter freundii strain ABC 2 and Serratia marcescens strain ADJ 212.

CONCLUSION

This study showed that MRB constitute a significant proportion of the bacterial community present in RTE salads served in Nigerian restaurants.

SIGNIFICANCE AND IMPACT OF THE STUDY

Our study provided empirical evidence which showed that RTE salads served in Nigerian restaurants were a potential source of MRB, with significant health risk.

Modelling the combined effect of chlorine, benzyl isothiocyanate, exposure time and cut size on the reduction of Salmonella in fresh-cut lettuce during washing process

This work aimed to study the effect of the combination of Sodium hypochlorite, the most used disinfectant by the vegetable industry, with a natural antimicrobial, benzyl-isothiocyanate (BITC), considering cutting surface and contact time, on the reduction of Salmonella in fresh-cut produce in washing operations under typical industrial conditions. Overall, the combinations of disinfectant and process parameters resulted in a mean reduction of Salmonella of 2.5 log CFU/g. According to statistical analysis, free chlorine and BITC concentrations, contact time and cut size exerted a significant effect on the Salmonella reduction (p ≤ 0.05). The optimum combination of process parameter values yielding the highest Salmonella reduction was a lettuce cut size of 15 cm2 washed for 110 s in industrial water containing 160 mg/L free chlorine and 40 mg/L BITC. A predictive model was also derived, which, as illustrated, could be applied to optimize industrial disinfection and develop probabilistic Exposure Assessments considering the effect of washing process parameters on the levels of Salmonella contamination in leafy green products. The present study demonstrated the efficacy of chlorine to reduce Salmonella populations in fresh-cut lettuce while highlighting the importance of controlling the washing process parameters, such as, contact time, cut size and concentration of the disinfectant to increase disinfectant efficacy and improve food safety.

Spontaneously fermented curly kale juice: Microbiological quality, nutritional composition, antioxidant, and antimicrobial properties

Nondairy fermented products, such as fruit and vegetable juices, are gaining popularity among consumers worldwide for health-related and economic reasons. The purpose of this study was to determine the changes in microbiological quality; antimicrobial and antioxidant activity; and phenolic, vitamin C, minerals, and cadmium content occurring during spontaneous fermentation of curly kale juice. The fermentation process contributed to a significant growth of lactic acid bacteria, enterococci, and yeasts, while no pathogens of Escherichia coli and Salmonella spp. were observed. The antimicrobial properties of the obtained juice improved during fermentation for all indicator microorganisms. Total phenolic content and antioxidant activity increased from 48 to 116 mg gallic acid equivalent/100 mL and from 4.5 to 6.8 mM Trolox/100 mL, respectively, while the content of vitamin C decreased. The results indicated that 100 mL of juice provided a significant contribution to the recommended mineral intake. Moreover, the content of heavy metal Cd was within acceptable limit (6 µg/kg). Overall, our findings indicate that fermented curly kale juice may become popular in the functional food sector, especially among vegetarians and consumers with lactose intolerance or allergy to milk proteins. PRACTICAL APPLICATION: As the market for fermented fruit and vegetable products grows, new plant materials rich in biologically active compounds are being sought. Considering the high demand for sauerkraut, the fermentation of other cruciferous vegetables seems interesting. One example is curly kale, which has been classified as "superfood" due to its numerous beneficial health properties, such as strong antioxidant activity, high vitamins, and minerals content. In addition, a market niche exists due to a lack of fermented green curly kale products on the market, making our study particularly relevant.

Biopreservation approaches to reduce Listeria monocytogenes in fresh vegetables

Two biopreservation approaches for fresh lettuce, rocket salad, parsley and spinach were studied. The potential of Pediococcus pentosaceus DT016, as a protective culture, to suppress Listeria monocytogenes in vegetables during storage was evaluated. The pathogen numbers in the vegetables inoculated with P. pentosaceus DT016 were significantly (p < 0.01) lower throughout the storage period and, at the last storage day, a minimum difference of 1.4 log CFU/g was reported when compared with the vegetables without the protective culture. Moreover, by using two levels of L. monocytogenes (about 6 and 4 log CFU/g), it was observed that the antagonist effect of P. pentosaceus was higher for the lower pathogen numbers. The second approach evaluated a pediocin DT016 solution to inactivate and control L. monocytogenes proliferation. The pathogen load was studied after washing with: water, chlorine and the pediocin solution and along storage at 4  °C. Comparing the various washing solutions, the vegetables washed with pediocin presented significantly (p < 0.01) lower pathogen numbers throughout storage, by a minimum of 3.2 and 2.7 log CFU/g, than in vegetables washed with water and chlorine, respectively. The proposed methodologies are promising alternatives to maintain the safety of fresh vegetables during extended storage at refrigeration temperature.