| 1. |
- Alsanius, Beatrix, et al.
(författare)
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Cool fruits - Effekter av lagringstid samt lagringstemperatur på förekomst av Listeria monocytogenes i färsk fruktcocktail
- 2022
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Färska fruktsallader (fruktcocktail) efterfrågas av konsumenter. Med dagens ansträngda elpriser ställs frågan om kyltemperaturen under framställning, transport och display i butiken skulle kunna höjas från 4 till 8 °C utan att äventyra livsmedelssäkerheten för dessa produkter. Föreliggande rapport bygger på en litteraturstudie och en provokationsstudie, där den köldtoleranta (psykrofila) organismen Listeria monocytogenes användes som modellorganism. Litteraturstudien genomfördes som en systematisk litteratursökning i databasen Web‐of‐Science. I den experimentella delen studerades tillväxtbeteendet av L. monocytogenes med hänsyn till lagringstemperatur och lagringstid i en färsk fruktcocktail bestående av ananas, röda äpplen, nätmelon och röda druvor. Den experimentella delen byggde på frågeställningen om lagringstemperaturen kan höjas från 4 °C till 8 °C samt från en rekommenderad lagringslängd på 4 dagar till 8 dagar, med hänsyn till förekomst av L. monocytogenes. En klinisk stam av L. monocytogenes inokulerades i färdiga råa fruktsallader. Tre temperaturregimer tillämpades: 4 °C i åtta dagar, 8 °C i åtta dagar samt 4 °C i ett dygn följt av 8 °C under återstående lagringstid på totalt åtta dagar (så kallad dynamisk temperaturregim). Vi fann att modellorganismen hade förökat sig efter åtta dagars lagringstid i samtliga behandlingar, dock avsevärt långsammare vid lagring i 4 °C, jämfört med kontinuerlig lagring i 8 °C samt den dynamiska behandlingen. Vid 4 °C lagringstemperatur visade L. monocytogenes en tillväxtpotential av knappt ett halvt log‐värde, samt med log 1,37 respektive log 1,23 vid 8 °C lagringstemperatur respektive dynamisk lagring, trots att fruktsalladens pH låg under minimi‐kraven för L. monocytogenes. I synnerhet i behandlingarna med högre temperatur förekom en massiv uppförökning av jästsvampar. Utifrån föreliggande resultat av litteraturundersökningen förordar vi ingen förhöjning av lagringstemperatur eller förlängning av lagringstid.
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| 2. |
- Lindblom, Tobias, et al.
(författare)
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High-throughput method for detection and quantification of lesions on leaf scale based on trypan blue staining and digital image analysis
- 2020
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Ingår i: Plant Methods. - : Springer Science and Business Media LLC. - 1746-4811. ; 16
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Tidskriftsartikel (refereegranskat)abstract
- Background: Field-grown leafy vegetables can be damaged by biotic and abiotic factors, or mechanically damaged by farming practices. Available methods to evaluate leaf tissue damage mainly rely on colour differentiation between healthy and damaged tissues. Alternatively, sophisticated equipment such as microscopy and hyperspectral cameras can be employed. Depending on the causal factor, colour change in the wounded area is not always induced and, by the time symptoms become visible, a plant can already be severely affected. To accurately detect and quantify damage on leaf scale, including microlesions, reliable differentiation between healthy and damaged tissue is essential. We stained whole leaves with trypan blue dye, which traverses compromised cell membranes but is not absorbed in viable cells, followed by automated quantification of damage on leaf scale.Results: We present a robust, fast and sensitive method for leaf-scale visualisation, accurate automated extraction and measurement of damaged area on leaves of leafy vegetables. The image analysis pipeline we developed automatically identifies leaf area and individual stained (lesion) areas down to cell level. As proof of principle, we tested the methodology for damage detection and quantification on two field-grown leafy vegetable species, spinach and Swiss chard.Conclusions: Our novel lesion quantification method can be used for detection of large (macro) or single-cell (micro) lesions on leaf scale, enabling quantification of lesions at any stage and without requiring symptoms to be in the visible spectrum. Quantifying the wounded area on leaf scale is necessary for generating prediction models for economic losses and produce shelf-life. In addition, risk assessments are based on accurate prediction of the relationship between leaf damage and infection rates by opportunistic pathogens and our method helps determine the severity of leaf damage at fine resolution.
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| 3. |
- Lindblom, Tobias, et al.
(författare)
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Processing of leafy vegetables matters: Damage and microbial community structure from field to bag
- 2021
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Ingår i: Food Control. - : Elsevier BV. - 0956-7135 .- 1873-7129. ; 125
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Tidskriftsartikel (refereegranskat)abstract
- Leafy vegetables undergo abiotic and biotic stresses, and a series of processing steps that cause mechanical injury. Breaching the epidermis alters phyllosphere structural and nutrient conditions, resulting in successional shifts in leaf microbiota and entry of human pathogens. This study examined damage during processing of baby leaves (Swiss chard, spinach) and concomitant microbial successional events. Machine-harvesting, washing, and packaging caused major phyllosphere perturbations, with increasing levels of leaf damage. Older leaves showed most damage, but plant species was influential. Diversity estimates of bacterial and fungal communities revealed shifts in microbiota post-harvest, particularly after the washing step. Relative abundance of Pseudomonadaceae and Enterobacteriaceae increased from field to bag. Bacterial species specific to different harvesting and processing steps replaced core microbiota species. While processing is unavoidable, procedures that mitigate leaf damage can enhance shelf-life and food safety.
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| 4. |
- Mogren, Lars, et al.
(författare)
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The hurdle approach-A holistic concept for controlling food safety risks associated with pathogenic bacterial contamination of leafy green vegetables. A review
- 2018
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Ingår i: Frontiers in Microbiology. - : Frontiers Media SA. - 1664-302X. ; 9:AUG
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Forskningsöversikt (refereegranskat)abstract
- Consumers appreciate leafy green vegetables such as baby leaves for their convenience and wholesomeness and for adding a variety of tastes and colors to their plate. In Western cuisine, leafy green vegetables are usually eaten fresh and raw, with no step in the long chain from seed to consumption where potentially harmful microorganisms could be completely eliminated, e.g., through heating. A concerning trend in recent years is disease outbreaks caused by various leafy vegetable crops and one of the most important foodborne pathogens in this context is Shiga toxin-producing Escherichia coli (STEC). Other pathogens such as Salmonella, Shigella, Yersinia enterocolitica and Listeria monocytogenes should also be considered in disease risk analysis, as they have been implicated in outbreaks associated with leafy greens. These pathogens may enter the horticultural value network during primary production in field or greenhouse via irrigation, at harvest, during processing and distribution or in the home kitchen/restaurant. The hurdle approach involves combining several mitigating approaches, each of which is insufficient on its own, to control or even eliminate pathogens in food products. Since the food chain system for leafy green vegetables contains no absolute kill step for pathogens, use of hurdles at critical points could enable control of pathogens that pose a human health risk. Hurdles should be combined so as to decrease the risk due to pathogenic microbes and also to improve microbial stability, shelf-life, nutritional properties and sensory quality of leafy vegetables. The hurdle toolbox includes different options, such as physical, physiochemical and microbial hurdles. The goal for leafy green vegetables is multi-target preservation through intelligently applied hurdles. This review describes hurdles that could be used for leafy green vegetables and their biological basis, and identifies prospective hurdles that need attention in future research.
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| 5. |
- Mulaosmanovic, Emina
(författare)
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Interactions between leaf lesions and the phyllosphere microbiota in leafy vegetables
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Leafy vegetables (baby leaves) are considered an important source and vector for transmission of foodborne pathogens to humans. Contamination can occur from farm to fork. Although ‘rare’, contamination events have a substantial impact on public health. The shigatoxigenic bacterium, Escherichia coli O157:H7, can establish on the surface (epiphyte) and interior (endophyte) of leaves. Natural openings and leaf lesions serve as entry points, and internalised bacterial cells are shielded from rinse water and sanitisers. In this thesis, a new method for scrutinising leaf lesions in leafy vegetables was developed and used to link leaf damage to the dynamics of E. coli O157:H7gfp+ and the indigenous microbiota in the phyllosphere, and to evaluate use of calcium fortification of leafy vegetables for damage reduction. The new approach combines trypan blue dye staining of whole leaves with digital image analysis for detection and automated quantification of damage, enabling assessment of lesion size, shape and position. Number of lesions and relative lesion area were found to be crop-specific and increased along the production chain, while diversity of the leaf-associated microbial community decreased upon entry of baby leaves to the cold chain. The size of individual lesions and damaged leaf area affected the depth of invasion into plant tissue, dispersal to adjacent areas and number of culturable E. coli O157:H7gfp+ directly after inoculation. However, differences in culturable E. coli O157:H7gfp+ retrieved from leaf macerate evened out after 2 days post-inoculation (dpi). Leaf spraying with calcium decreased the number of lesions and damaged area on spinach leaves, lowering log CFU E. coli cm-2 detached at 0 and 1 dpi. Overall, the results in this thesis question the assumption that macroscopically intact leaves are free of lesions and safe. The method developed can assist in establishment of hurdles for preventing transmission of foodborne pathogens via baby leaves.
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| 6. |
- Mulaosmanovic, Emina, et al.
(författare)
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Size Matters: Biological and Food Safety Relevance of Leaf Damage for Colonization of Escherichia coli O157:H7 gfp
- 2021
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Ingår i: Frontiers in Microbiology. - : Frontiers Media SA. - 1664-302X. ; 11
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Tidskriftsartikel (refereegranskat)abstract
- This study examined the biological and food safety relevance of leaf lesions for potential invasion of food pathogens into the plant tissue (internalization). This was done by determining the role of artificial leaf damage in terms of damaged leaf area on proliferation of E. coli O157:H7 gfp+. In a two-factorial experiment, unwashed fresh baby leaf spinach (Spinacia oleracea L.) was subjected to four damage levels (undamaged, low, moderate, high damage; factor 1) and three incubation intervals (0, 1, 2 days post-inoculation; factor 2). Individual leaves were immersed for 15 s in a suspension loaded with E. coli O157:H7 gfp+ (106 CFU × mL–1). The leaves were analyzed individually using image analysis tools to quantify leaf area and number and size of lesions, and using confocal laser scanning and scanning electron microscopy to visualize leaf lesions and presence of the introduced E. coli strain on and within the leaf tissue. Prevalence of E. coli O157:H7 gfp+ was assessed using a culture-dependent technique. The results showed that size of individual lesions and damaged leaf area affected depth of invasion into plant tissue, dispersal to adjacent areas, and number of culturable E. coli O157:H7 gfp+ directly after inoculation. Differences in numbers of the inoculant retrieved from leaf macerate evened out from 2 days post-inoculation, indicating rapid proliferation during the first day post-inoculation. Leaf weight was a crucial factor, as lighter spinach leaves (most likely younger leaves) were more prone to harbor E. coli O157:H7 gfp+, irrespective of damage level. At the high inoculum density used, the risk of consumers’ infection was almost 100%, irrespective of incubation duration or damage level. Even macroscopically intact leaves showed a high risk for infection. These results suggest that the risk to consumers is correlated with how early in the food chain the leaves are contaminated, and the degree of leaf damage. These findings should be taken into account in different steps of leafy green processing. Further attention should be paid to the fate of viable, but non-culturable, shiga-toxigenic E. coli on and in ready-to-eat leafy vegetables.
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| 7. |
- Sousa, Maria, et al.
(författare)
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Volatilomes reveal specific signatures for contamination of leafy vegetables with Escherichia coli O157:H7
- 2023
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Ingår i: Food Control. - : Elsevier BV. - 0956-7135 .- 1873-7129. ; 146
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Tidskriftsartikel (refereegranskat)abstract
- Transmission of foodborne pathogens by plants, especially shiga toxin-producing Escherichia coli, has become a public health concern for ready-to-eat products. Due to the patchy distribution of foodborne pathogens on commodities, random sampling before processing and following packaging cannot reliably exclude presence of pathogenic microbes. Robust, cost-effective, and reliable methods for monitoring pathogenic E. coli on fresh produce are therefore urgently needed. We investigated whether volatile organic compounds are suitable for detection of E. coli O157:H7 contamination of leafy vegetables. Using solid-phase microextraction coupled with gas chromatography-mass spectrometry, we analyzed volatilomes of spinach (Spinacia oleracea L.) and rocket (Eruca sativa L.) leaf lysates, and of a common culture medium (lysogeny broth), in the presence and absence of E. coli O157:H7. Volatile profiles varied with the nutrient medium. We found higher proportions of indole, phenylmethanol, 2-methoxyphenol, ethanol, propan-1-ol, decan-1-ol, tridecan-1-ol, nonan-2-one and tridecan-2-one in headspace from inoculated compared with non-inoculated samples. This demonstrates that volatile organic compounds are suitable for detecting contamination of leafy vegetables with E. coli O157:H7. In future work we will focus on adapting the volatile assay for screening for E. coli O157:H7 contamination under different conditions, including intact and damaged baby leaves, leaf packages, or leaf batches, and on increasing its sensitivity.
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| 8. |
- Vågsholm, Ivar, et al.
(författare)
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Safety risks associated with dispersal of E. coli O157:H7 in home sprouting modules
- 2019
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Ingår i: Food Science and Technology. - : Elsevier BV. - 0023-6438 .- 1096-1127. ; 101, s. 783-788
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Tidskriftsartikel (refereegranskat)abstract
- Despite numerous outbreaks of foodborne illnesses associated with sprouts, consumption of raw sprouted seeds is still linked with a healthy lifestyle in Scandinavia. Different types of sprouting modules for home sprout production are available on the market, and sold without information about risks associated with sprouting. During sprouting, conditions are ideal for seed emergence, but also for bacterial proliferation. Moreover, since seeds used for sprouting are non-sterile, human pathogens may propagate within sprouting modules. This study assessed vertical dispersal of Escherichia coli strain O157:H7 in two types of three-layered sprouting modules intended for home sprouting. Organic fenugreek seeds were artificially inoculated and transferred to either the top or bottom layer of sprouting modules. As commensal bacterial biota can affect survival of an artificially introduced strain, but can also contain pathogens, culturable bacterial species on fenugreek seeds were evaluated. A Beta-Poisson model was used to assess the risk of consumer exposure to the artificially introduced strain when added to seeds in the top or bottom layer. We found that the inoculated strain dispersed vertically up and down between the layers and that the risk of bacterial dispersal was high in either direction, posing a high risk of consumer exposure.
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