Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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    Moderate intensity Pulsed Electric Fields (PEF) as alternative mild preservation technology for fruit juice
    Timmermans, R.A.H. ; Mastwijk, H.C. ; Berendsen, L.B.J.M. ; Nederhoff, A.L. ; Matser, A.M. ; Boekel, M.A.J.S. Van; Nierop Groot, M.N. - \ 2019
    International Journal of Food Microbiology 298 (2019). - ISSN 0168-1605 - p. 63 - 73.
    Electric field strength - Microbiology - Ohmic heating - Preservation - Pulse width - Thermal reference

    Moderate intensity Pulsed Electric Fields (PEF) was studied for microbial inactivation as an alternative to high intensity PEF or to classical thermal pasteurization. The process is characterized by the application of electric pulses, allowing an increase of the product temperature by the ohmic heat generated by the pulses. A systematic evaluation of the effect of parameters electric field strength (E) and pulse width (τ) on the inactivation of Escherichia coli, Listeria monocytogenes, Lactobacillus plantarum, Salmonella Senftenberg and Saccharomyces cerevisiae in orange juice was carried out in a continuous flow system. A wide range of conditions was evaluated, and both E and τ were shown to be important in the efficacy to inactivate micro-organisms. Remarkably, PEF conditions at E = 2.7 kV/cm and τ = 15–1000 μs showed to be more effective in microbial inactivation than at E = 10 kV/cm and τ = 2 μs. Inactivation kinetics of the tested PEF conditions were compared to an equivalent thermal process to disentangle non-thermal effects (electroporation) from thermal effects responsible for the microbial inactivation. At standard high intensity PEF treatment a non-thermal inactivation at E = 20 kV/cm and τ = 2 μs pulses was observed and attributed to electroporation. Non-thermal effects could also be resolved with moderate intensity PEF at E = 2.7 kV/cm and pulse width between τ = 15–1000 μs. Microbial inactivation at these moderate intensity PEF conditions was studied in more detail at different pH and medium conductivity for E. coli and L. monocytogenes in watermelon juice and coconut water. Under moderate intensity PEF conditions the effectiveness of treatment was independent of pH for all evaluated matrices in the pH range of 3.8–6.0, whereas under high intensity PEF conditions the pH of the product is a critical factor for microbial inactivation. This suggests that the inactivation proceeds through a different mechanism at moderate intensity PEF, and speculations for this mechanism are presented. In conclusion, moderate intensity PEF conditions at E = 2.7 kV/cm and pulse width of 15–1000 μs has potential for industrial processing for the preservation of fruit juices and pH neutral liquid food products.

    The eukaryotic ancestor shapes up
    Eme, Laura ; Ettema, Thijs J.G. - \ 2018
    Nature 562 (2018)7727. - ISSN 0028-0836 - p. 352 - 353.
    Cell biology - Evolution - Microbiology
    Understanding preferences for interventions to reduce microbiological contamination in Dutch vegetable production
    Asseldonk, M.A.P.M. Van; Malaguti, L. ; Breukers, M.L.H. ; Fels, H.J. van der - \ 2018
    Journal of Food Protection 81 (2018)6. - ISSN 0362-028X - p. 892 - 897.
    Behavior - Fresh produce - Incentive - Microbiology - Pathogen

    Understanding growers' preferences regarding interventions to improve the microbiological safety of their produce could help to design more effective strategies for the adoption of such food safety measures by growers. The objective of this survey study was to obtain insights for the design of interventions that could stimulate growers to increase the frequency of irrigation water sampling and water testing to reduce possible microbiological contamination of their fresh produce. The results showed that price intervention, referring to making the intervention less costly by reducing the price via discounts, is the most effective strategy to change growers' intentions to increase their frequency of irrigation water testing. Moreover, a sense of urgency affects their intentions to increase the frequency of irrigation water testing. The findings of this survey support the hypothesis that, to date, safety is not perceived as a quality control issue under normal circumstances, but safety becomes an overriding attribute in a food crisis.

    Interaction networks, ecological stability, and collective antibiotic tolerance in polymicrobial infections
    Vos, Marjon G.J. de; Zagorski, Marcin ; McNally, Alan ; Bollenbach, Tobias - \ 2017
    Proceedings of the National Academy of Sciences of the United States of America 114 (2017)40. - ISSN 0027-8424 - p. 10666 - 10671.
    Antibiotics - Infection - Microbiology - Systems biology

    Polymicrobial infections constitute small ecosystems that accommodate several bacterial species. Commonly, these bacteria are investigated in isolation. However, it is unknown to what extent the isolates interact and whether their interactions alter bacterial growth and ecosystem resilience in the presence and absence of antibiotics. We quantified the complete ecological interaction network for 72 bacterial isolates collected from 23 individuals diagnosed with polymicrobial urinary tract infections and found that most interactions cluster based on evolutionary relatedness. Statistical network analysis revealed that competitive and cooperative reciprocal interactions are enriched in the global network, while cooperative interactions are depleted in the individual host community networks. A population dynamics model parameterized by our measurements suggests that interactions restrict community stability, explaining the observed species diversity of these communities. We further show that the clinical isolates frequently protect each other from clinically relevant antibiotics. Together, these results highlight that ecological interactions are crucial for the growth and survival of bacteria in polymicrobial infection communities and affect their assembly and resilience.

    First step in using molecular data for microbial food safety risk assessment; hazard identification of Escherichia coli O157 : H7 by coupling genomic data with in vitro adherence to human epithelial cells
    Pielaat, Annemarie ; Boer, M.P. ; Wijnands, Lucas M. ; Hoek, A.H.A.M. van; Bouw, El ; Barker, G.C. ; Teunis, P.F.M. ; Aarts, Henk J.M. ; Franz, Eelco - \ 2015
    International Journal of Food Microbiology 213 (2015). - ISSN 0168-1605 - p. 130 - 138.
    GWAS - Microbiology - Risk assessment - SNP - STEC

    The potential for using whole genome sequencing (WGS) data in microbiological risk assessment (MRA) has been discussed on several occasions since the beginning of this century. Still, the proposed heuristic approaches have never been applied in a practical framework. This is due to the non-trivial problem of mapping microbial information consisting of thousands of loci onto a probabilistic scale for risks. The paradigm change for MRA involves translation of multidimensional microbial genotypic information to much reduced (integrated) phenotypic information and onwards to a single measure of human risk (i.e. probability of illness).In this paper a first approach in methodology development is described for the application of WGS data in MRA; this is supported by a practical example. That is, combining genetic data (single nucleotide polymorphisms; SNPs) for Shiga toxin-producing Escherichia coli (STEC) O157 with phenotypic data (in vitro adherence to epithelial cells as a proxy for virulence) leads to hazard identification in a Genome Wide Association Study (GWAS).This application revealed practical implications when using SNP data for MRA. These can be summarized by considering the following main issues: optimum sample size for valid inference on population level, correction for population structure, quantification and calibration of results, reproducibility of the analysis, links with epidemiological data, anchoring and integration of results into a systems biology approach for the translation of molecular studies to human health risk.Future developments in genetic data analysis for MRA should aim at resolving the mapping problem of processing genetic sequences to come to a quantitative description of risk. The development of a clustering scheme focusing on biologically relevant information of the microbe involved would be a useful approach in molecular data reduction for risk assessment.

    Colonic metaproteomic signatures of active bacteria and the host in obesity
    Kolmeder, C.A. ; Ritari, Jarmo ; Verdam, F.J. ; Vos, W.M. de - \ 2015
    Proteomics 15 (2015)20. - ISSN 1615-9853 - p. 3544 - 3552.
    Composition - Intestinal microbiota - Metaproteomics - Microbiology - Obesity

    Obesity is associated with the intestinal microbiota in humans but the underlying mechanisms are yet to be fully understood. Our previous phylogenetic study showed that the faecal microbiota profiles of nonobese versus obese and morbidly obese individuals differed. Here, we have extended this analysis with a characterization of the faecal metaproteome, in order to detect differences at a functional level. Proteins were extracted from crude faecal samples of 29 subjects, separated by 1D gel electrophoresis and characterized using RP LC-MS/MS. The peptide data were analyzed in database searches with two complementary algorithms, OMSSA and X!Tandem, to increase the number of identifications. Evolutionary genealogy of genes: nonsupervised orthologous groups (EggNOG) database searches resulted in the functional annotation of over 90% of the identified microbial and human proteins. Based on both bacterial and human proteins, a clear clustering of obese and nonobese samples was obtained that exceeded the phylogenetic separation in dimension. Moreover, integration of the metaproteomics and phylogenetic datasets revealed notably that the phylum Bacteroidetes was metabolically more active in the obese than nonobese subjects. Finally, significant correlations between clinical measurements and bacterial gene functions were identified. This study emphasizes the importance of integrating data of the host and microbiota to understand their interactions.

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