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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    Inactivation of H-type and L-type bovine spongiform encephalopathy following recommended autoclave decontamination procedures
    Chapman, Gail E. ; Lockey, Richard ; Beck, Katy E. ; Vickery, Chris ; Arnold, Mark ; Thorne, Leigh ; Thorne, Jemma K. ; Walker, Sarah R. ; Keulen, Lucien van; Casalone, Cristina ; Griffiths, Peter C. ; Simmons, Marion M. ; Terry, Linda A. ; Spiropoulos, John - \ 2020
    Transboundary and Emerging Diseases (2020). - ISSN 1865-1674
    bovine spongiform encephalopathy - H-type - inactivation - L-type - transmissible spongiform encephalopathie

    The resistance of H-type and L-type BSE prions to autoclaving under EU regulation conditions for specified risk material is unknown. We employed transgenic mouse (bovinized line tg1896) bioassay to assess the efficacy of such decontamination on L- and H-type BSE. For each source, titre calculation was based on the comparison of incubation period and attack rate prior to and after decontamination. The infectious titre of L-type BSE was reduced by at least 9.40 log10 and of H-type BSE by at least 3.94 log10. In fact, no infectivity was detected for L-type or H-type BSE post-inactivation even at a 10–1 dilution.

    Impact of microbial variability on food safety and quality
    Aryani, D.C. - \ 2016
    Wageningen University. Promotor(en): Marcel Zwietering, co-promotor(en): Heidy den Besten. - Wageningen : Wageningen University - ISBN 9789462577381 - 190
    listeria monocytogenes - lactobacillus plantarum - growth analysis - kinetics - growth models - inactivation - heat stress - strain differences - food safety - milk - ham - microbial diversity - food quality - listeria monocytogenes - lactobacillus plantarum - groeianalyse - kinetica - groeimodellen - inactivatie - warmtestress - stamverschillen - voedselveiligheid - melk - ham - microbiële diversiteit - voedselkwaliteit
    Reducing viral contamination from finger pads: handwashing is more effective than alcohol-based hand disinfectants
    Tuladhar, E. ; Hazeleger, W.C. ; Koopmans, M. ; Zwietering, M.H. ; Duizer, E. - \ 2015
    Journal of Hospital Infection 90 (2015)3. - ISSN 0195-6701 - p. 226 - 234.
    feline calicivirus - murine norovirus - foodborne viruses - norwalk virus - in-vivo - inactivation - sanitizer - surrogate - efficacy - food
    Background - Hand hygiene is important for interrupting transmission of viruses through hands. Effectiveness of alcohol-based hand disinfectant has been shown for bacteria but their effectiveness in reducing transmission of viruses is ambiguous. Aim - To test efficacy of alcohol hand disinfectant against human enteric and respiratory viruses and to compare efficacy of an alcohol-based hand disinfectant and handwashing with soap and water against norovirus. Methods - Efficacies of a propanol and an ethanol-based hand disinfectant against human enteric and respiratory viruses were tested in carrier tests. Efficacy of an alcohol-based hand disinfectant and handwashing with soap and water against noroviruses GI.4, GII.4, and MNV1 were tested using finger pad tests. Findings - The alcohol-based hand disinfectant reduced the infectivity of rotavirus and influenza A virus completely within 30 s whereas poliovirus Sabin 1, adenovirus type 5, parechovirus 1, and MNV1 infectivity were reduced 3.0 ± 0.4 log10) was significantly higher than treating hands with alcohol (2.8 ± 1.5 log10). Washing with soap and water for 30 s removed genomic copies of MNV1 (>5 log10), noroviruses GI.4 (>6 log10), and GII.4 (4 log10) completely from all finger pads. Treating hands with propanol-based hand disinfectant showed little or no reduction to complete reduction with mean genomic copy reduction of noroviruses GI.4, GII.4, and MNV1 being >2.6, >3.3, and >1.2 log10 polymerase chain reaction units respectively. Conclusions - Washing hands with soap and water is better than using alcohol-based hand disinfectants in removing noroviruses from hands. Keywords: Carrier test; Enteric virus; Finger pad test; Foodborne viruses; Hand disinfection; Norovirus; Respiratory viruses
    Diversity of acid stress resistant variants of Listeria monocytogenes and the potential role of ribosomal protein S21 encoded by rpsU
    Metselaar, K.I. ; Besten, H.M.W. den; Boekhorst, J. ; Hijum, S.A.F.T. van; Zwietering, M.H. ; Abee, T. - \ 2015
    Frontiers in Microbiology 6 (2015). - ISSN 1664-302X - 12 p.
    high hydrostatic-pressure - gamma-aminobutyric-acid - microtiter plate assay - glutamate-decarboxylase - bacillus-subtilis - escherichia-coli - low ph - genes - strains - inactivation
    The dynamic response of microorganisms to environmental conditions depends on the behavior of individual cells within the population. Adverse environments can select for stable stress resistant subpopulations. In this study, we aimed to get more insight in the diversity within Listeria monocytogenes LO28 populations, and the genetic basis for the increased resistance of stable resistant fractions isolated after acid exposure. Phenotypic cluster analysis of 23 variants resulted in three clusters and four individual variants and revealed multiple-stress resistance, with both unique and overlapping features related to stress resistance, growth, motility, biofilm formation, and virulence indicators. A higher glutamate decarboxylase activity correlated with increased acid resistance. Whole genome sequencing revealed mutations in rpsU, encoding ribosomal protein S21 in the largest phenotypic cluster, while mutations in ctsR, which were previously shown to be responsible for increased resistance of heat and high hydrostatic pressure resistant variants, were not found in the acid resistant variants. This underlined that large population diversity exists within one L. monocytogenes strain and that different adverse conditions drive selection for different variants. The finding that acid stress selects for rpsU variants provides potential insights in the mechanisms underlying population diversity of L. monocytogenes.
    Quantification of transmission of foot-and-mouth disease virus caused by an environment contaminated with secretions and excretions from infected calves
    Bravo De Rueda, C. ; Jong, M. de; Eblé, P.L. ; Dekker, A. - \ 2015
    Veterinary Research 46 (2015). - ISSN 0928-4249
    between-pen transmission - classical swine-fever - vaccinated pigs - actinobacillus-pleuropneumoniae - influenza-viruses - dairy-cows - inactivation - campylobacter - formaldehyde - populations
    Foot-and-mouth disease virus (FMDV) infected animals can contaminate the environment with their secretions and excretions. To quantify the contribution of a contaminated environment to the transmission of FMDV, this study used calves that were not vaccinated and calves that were vaccinated 1 week prior to inoculation with the virus in direct and indirect contact experiments. In direct contact experiments, contact calves were exposed to inoculated calves in the same room. In indirect contact experiments, contact calves were housed in rooms that previously had held inoculated calves for three days (either from 0 to 3 or from 3 to 6 days post inoculation). Secretions and excretions from all calves were tested for the presence of FMDV by virus isolation; the results were used to quantify FMDV transmission. This was done using a generalized linear model based on a 2 route (2R, i.e. direct contact and environment) SIR model that included information on FMDV survival in the environment. The study shows that roughly 44% of transmission occurs via the environment, as indicated by the reproduction ratio ^R0 2R environment that equalled 2.0, whereas the sum of ^R0 2R contact and ^R0 2R environment equalled 4.6. Because vaccination 1 week prior to inoculation of the calves conferred protective immunity against FMDV infection, no transmission rate parameters could be estimated from the experiments with vaccinated calves. We conclude that a contaminated environment contributes considerably to the transmission of FMDV therefore that hygiene measures can play a crucial role in FMD control.
    Establishing Guidelines to Retain Viability of Probiotics during Spray Drying
    Perdana, J.A. ; Fox, M.B. ; Boom, R.M. ; Schutyser, M.A.I. - \ 2015
    Drying Technology 33 (2015)13. - ISSN 0737-3937 - p. 1560 - 1569.
    lactobacillus-plantarum wcfs1 - inactivation - integration - isotherms - products - sorption - storage - trends - foods - model
    We present the application of a model-based approach to map processing conditions suitable to spray dry probiotics with minimal viability loss. The approach combines the drying history and bacterial inactivation kinetics to predict the retention of viability after drying. The approach was used to systematically assess the influence of operational co-current spray drying conditions on residual viability. Moreover, two promising alternative drying strategies for probiotics were evaluated involving encapsulation in a hollow particle and using an ‘ideal-mixed’ dryer system. Finally, a graph was constructed with the model to provide visual guidelines to optimize spray dying for probiotics in terms of viability and drying efficiency.
    Physiological and transcriptional response of Bacillus cereus treated with low-temperature nitrogen gas plasma
    Mols, J.M. ; Mastwijk, H.C. ; Nierop Groot, M.N. ; Abee, T. - \ 2013
    Journal of Applied Microbiology 115 (2013)3. - ISSN 1364-5072 - p. 689 - 702.
    atmospheric-pressure - escherichia-coli - argon plasma - in-vitro - sterilization - inactivation - identification - bacteria - efficacy - stress
    Aims - This study was conducted to investigate the inactivation kinetics of Bacillus cereus vegetative cells upon exposure to low-temperature nitrogen gas plasma and to reveal the mode of inactivation by transcriptome profiling. Methods and Results - Exponentially growing B. cereus cells were filtered and put on agar plates. The plates, carrying the filters with the vegetative cells, were placed into low-temperature nitrogen gas plasma at atmospheric pressure. After different exposure times, the cells were harvested for RNA extraction and enumeration. The RNA was used to perform whole-transcriptome profiling using DNA microarrays. The transcriptome profile showed a large overlap with profiles obtained from conditions generating reactive oxygen species in B. cereus. However, excess radicals such as peroxynitrite, hydroxyl and superoxide could not be detected using radical-specific fluorescence staining. Lack of UV-specific responses including factors involved in DNA damage repair is in line with the absence of UV-specific emission in the afterglow of the nitrogen gas plasma as analysed using optical emission spectroscopy (OES). Conclusions - Antibacterial activity of nitrogen gas plasma is not based on UV radiation. Exposure to nitrogen gas plasma leads to oxidative stress and inactivation of targeted cells. A secondary oxidative stress with the indicative formation of reactive oxygen species within cells could not be observed. Significance and Impact of the Study - This study represents the first investigation of differential gene expression on a genome-wide scale in B. cereus following nitrogen gas plasma exposure. This study may help to design economically feasible, safe and effective plasma decontamination devices
    Isolation and quantification of highly acid resistant variants of Listeria monocytogenes
    Metselaar, K.I. ; Besten, H.M.W. den; Abee, T. ; Moezelaar, R. ; Zwietering, M.H. - \ 2013
    International Journal of Food Microbiology 166 (2013)3. - ISSN 0168-1605 - p. 508 - 514.
    high hydrostatic-pressure - tolerance response - low ph - stress - virulence - survival - strains - lo28 - inactivation - pathogen
    Heterogeneity in stress response of bacteria is one of the biggest challenges posed by minimal processing, which aims at finding the balance between microbiologically stable foods while maintaining the characteristics of fresh products. In this study, exposure of Listeria monocytogenes LO28 to acid stress, which can be encountered in the food processing environment as well as in the human body upon ingestion, led to inactivation kinetics showing considerable tailing, which was described by a biphasic inactivation model. Stable acid resistant variants of L. monocytogenes LO28 were isolated after exposure of late-exponential phase cells to pH 3.5 for 90 min. The resulting 23 stable resistant isolates could be divided in three groups: (a) highly increased acid resistance (<1 log10 reduction, n = 16), (b) slightly increased acid resistance (1–3 log10 reduction, n = 6), and (c) one isolate showing a variable acid stress response. The highly acid resistant group showed increased resistance to the tested pH range of 2.5 to 3.5 in both late-exponential and stationary phase. Increased acid resistance showed to be significantly correlated to reduced growth rate. The Weibull model was reparameterized, resulting in improved parameter estimation, and was used to estimate the inactivation kinetics at mild pH. Studying the growth boundaries of the wild type and a representative set of variants indicated that the increased resistance of the variants was only related to survival of severe pH stress but did not allow for better growth or survival at mild pH stress. This study shows that acid exposure of late-exponential phase cells reveals the presence of acid resistant subpopulations and that there is a phenotypic diversity amongst them. The occurrence of heterogeneity and stress resistant subpopulations may lead to a higher number of surviving microorganisms than expected. Also, stress resistant subpopulations can become part of the domestic flora in a food production line. The currently isolated acid resistant variants are a new group of stress resistant variants and underline the importance of gaining more insight in the mechanisms underlying this heterogeneity and increased resistance. Keywords: Lethal pH; Subpopulations; Growth boundary; Heterogeneity; Inactivation kinetics
    Alternating electric fields combined with activated carbon for disinfection of Gram negative and Gram positive bacteria in fluidized bed electrode system
    Racyte, J. ; Bernard, S. ; Paulitsch-Fuchs, A.H. ; Yntema, D.R. ; Bruning, H. ; Rijnaarts, H.H.M. - \ 2013
    Water Research 47 (2013)16. - ISSN 0043-1354 - p. 6395 - 6405.
    water treatment plants - urban waste-water - antibiotic-resistance - antimicrobial activity - escherichia-coli - inactivation - particles - cells - flow - viability
    Strong electric fields for disinfection of wastewaters have been employed already for several decades. An innovative approach combining low strength (7 V/cm) alternating electric fields with a granular activated carbon fluidized bed electrode (FBE) for disinfection was presented recently. For disinfection performance of FBE several pure microbial cultures were tested: Bacillus subtilis, Bacillus subtilis subsp. subtilis, Enterococcus faecalis as representatives from Gram positive bacteria and Erwinia carotovora, Pseudomonas luteola, Pseudomonas fluorescens and Escherichia coli YMc10 as representatives from Gram negative bacteria. The alternating electric field amplitude and shape were kept constant. Only the effect of alternating electric field frequency on disinfection performance was investigated. From the bacteria tested, the Gram negative strains were more susceptible and the Gram positive microorganisms were more resistant to FBE disinfection. The collected data indicate that the efficiency of disinfection is frequency and strain dependent. During 6 h of disinfection, the decrease above 2 Log units was achieved with P. luteola and E. coli at 10 kHz and at dual frequency shift keying (FSK) modulated signal with frequencies of 10 kHz and 140 kHz. FBE technology appears to offer a new way for selective bacterial disinfection, however further optimizations are needed on treatment duration, and energy input, to improve effectiveness.
    Mimicking spray drying by drying of single droplets deposited on a flat surface
    Perdana, J.A. ; Fox, M.B. ; Schutyser, M.A.I. ; Boom, R.M. - \ 2013
    Food Bioprocess Technology 6 (2013)4. - ISSN 1935-5130 - p. 964 - 977.
    particle formation - kinetics - evaporation - inactivation - heat - simulation - levitator - models - layer - slabs
    The inactivation of bioactive ingredients during spray drying is often matrix specific. Therefore, the design of new processes or the optimisation of existing spray drying processes is usually highly product specific and requires numerous experiments. Rapid experimentation methods that facilitate fast data generation are therefore desired. A novel method for drying single droplets to mimic spray drying is proposed. The approach involves droplet deposition on a hydrophobic flat surface followed by controlled drying. A heat and mass transfer model is applied to predict the drying history of the single droplets. The approach is successfully evaluated through studying the inactivation of ß-galactosidase during drying. The heat and mass transfer model supplemented with inactivation kinetics provided reasonable prediction of the residual enzyme activity after drying. In addition, the inactivation kinetics could be directly extracted from single droplet experiments rather than using the kinetics from separate heating experiments. Finally, it was demonstrated that the inactivation kinetics found with the single-drop experiments could satisfactorily predict the residual activity of ß-galactosidase dried with a laboratory-scale spray dryer.
    Virucidal efficacy of hydrogen peroxide vapour disinfection
    Tuladhar, E. ; Terpstra, P. ; Koopmans, M. ; Duizer, E. - \ 2012
    Journal of Hospital Infection 80 (2012)2. - ISSN 0195-6701 - p. 110 - 115.
    time rt-pcr - feline calicivirus - chemical disinfection - murine norovirus - decontamination - inactivation - surfaces - spread - contamination - environment
    Background: Viral contamination of surfaces is thought to be important in transmission. Chemical disinfection can be an effective means of intervention, but little is known about the virucidal efficacy of hydrogen peroxide vapour (HPV) against enteric and respiratory viruses. Aim: To measure the virucidal efficacy of HPV against respiratory and enteric viruses on materials representing those found in institutions and homes. Methods: Poliovirus, human norovirus genogroup II. 4 (GII. 4), murine norovirus 1, rotavirus, adenovirus and influenza A (H1N1) virus dried on to stainless steel, framing panel and gauze carriers were exposed to HPV 127 ppm for 1 h at room temperature in an isolator. Poliovirus was also exposed to HPV at different locations in a room. The virucidal effect was measured by comparing recoverable viral titres against unexposed controls. Polymerase chain reaction was used to evaluate the effect of HPV on viral genome reduction. Findings: HPV disinfection resulted in complete inactivation of all viruses tested, characterized by >4 log(10) reduction in infectious particles for poliovirus, rotavirus, adenovirus and murine norovirus on stainless steel and framing panel carriers, and >2 log(10) reduction for influenza A virus on stainless steel and framing panel carriers, and for all viruses on gauze carriers. Complete inactivation of poliovirus was demonstrated at several locations in the room. Reductions in viral genomes were minimal on framing panel and gauze carriers but significant on stainless steel carriers; human norovirus GII. 4 genome was most resistant to HPV treatment. Conclusion: HPV could be an effective virucidal against enteric and respiratory viruses contaminating in-house environments. (C) 2011 The Healthcare Infection Society.
    Headspace fingerprinting as an untargeted approach to compare novel and traditional processing technologies: A case-study on orange juice pasteurisation
    Vervoort, L. ; Grauwet, T. ; Kebede, T. ; Plancken, I. van der; Timmermans, R.A.H. ; Hendrickx, M. ; Loey, A. van - \ 2012
    Food Chemistry 134 (2012)4. - ISSN 0308-8146 - p. 2303 - 2312.
    electric-field processes - high-pressure - mild pasteurization - storage - flavor - quality - pectinesterase - inactivation - temperature - impact
    As a rule, previous studies have generally addressed the comparison of novel and traditional processing technologies by a targeted approach, in the sense that only the impact on specific quality attributes is investigated. By contrast, this work focused on an untargeted strategy, in order to take into account unexpected and unintended effects of (novel) processing, and to possibly uncover unknown compounds resulting from alternative processing. The potential of headspace GC–MS fingerprinting was explored as a tool to compare the impact of thermal, high pressure (HP) and pulsed electric field (PEF) processing for mild pasteurisation of orange juice. This study demonstrated that when processing conditions are selected based on equivalent microbial safety, the impact of heat, HP and PEF pasteurisation on the volatile profile of orange juice can be considered comparable. During refrigerated storage, however, indirect impact differences were revealed, which were attributed to differences in degree of enzyme inactivation
    Thermal stability of structurally different viruses with proven or potential relevance to food safety
    Tuladhar, E. ; Bouwknegt, M. ; Zwietering, M.H. ; Koopmans, M. ; Duizer, E. - \ 2012
    Journal of Applied Microbiology 112 (2012)5. - ISSN 1364-5072 - p. 1050 - 1057.
    avian influenza-virus - murine norovirus - feline calicivirus - human parechovirus - inactivation - pcr - surface - heat - enteroviruses - disinfection
    Aims: To collect comparative data on thermal stability of structurally different viruses with proven or potential relevance to food safety. Methods and Results: Suspensions with poliovirus Sabin1, adenovirus type5, parechovirus1, human norovirus (NoV) GII.4, murine NoV (MNV1) and human influenza A (H1N1) viruses were heated at 56 and 73°C. Infectivity was tested by culture assay for all but human NoV GII.4 that cannot be cultivated in vitro. Time to first log10 reduction (TFL-value) was calculated based on best fit using the monophasic, biphasic or Weibull models. The Weibull model provided the best fit at 56°C for all viruses except influenza virus. The TFL at 56°C varied between a high of 27 min (parechovirus) to a low of 10 s (adenovirus) and ranked parechovirus > influenza > MNV1 > poliovirus > adenovirus. The monophasic model best described the behaviour of the viruses at 73°C, in which case the TFL was MNV1(62s) > influenza > adenovirus > parechovirus > poliovirus(14s). Conclusions: Viruses do not follow log-linear thermal inactivation kinetics and the thermostability of parechovirus and influenza virus is similar to that of proven foodborne viruses. Significance and Impact of the Study: Resistant fractions of viruses may remain infectious in thermal inactivation processes and inactivation of newly discovered or enveloped viruses in thermal food preparation processes should not be assumed without further testing.
    Effects of Temperature, Relative Humidity, Absolute Humidity, and Evaporation Potential on Survival of Airborne Gumboro Vaccine Virus
    Zhao, Y. ; Aarnink, A.J.A. ; Dijkman, R. ; Fabri, T. ; Jong, M.C.M. de; Groot Koerkamp, P.W.G. - \ 2012
    Applied and Environmental Microbiology 78 (2012)4. - ISSN 0099-2240 - p. 1048 - 1054.
    infectious bursal disease - air-borne bacteria - enterococcus-faecalis - bioaerosol samplers - 2001 epidemic - inactivation - aerosolization - transmission - poultry - spray
    Survival of airborne virus influences the extent of disease transmission via air. How environmental factors affect viral survival is not fully understood. We investigated the survival of a vaccine strain of Gumboro virus which was aerosolized at three temperatures (10°C, 20°C, and 30°C) and two relative humidities (RHs) (40% and 70%). The response of viral survival to four metrics (temperature, RH, absolute humidity [AH], and evaporation potential [EP]) was examined. The results show a biphasic viral survival at 10°C and 20°C, i.e., a rapid initial inactivation in a short period (2.3 min) during and after aerosolization, followed by a slow secondary inactivation during a 20-min period after aerosolization. The initial decays of aerosolized virus at 10°C (1.68 to 3.03 ln % min-1) and 20°C (3.05 to 3.62 ln % min-1) were significantly lower than those at 30°C (5.67 to 5.96 ln % min-1). The secondary decays at 10°C (0.03 to 0.09 ln % min-1) tended to be higher than those at 20°C (-0.01 to 0.01 ln % min-1). The initial viral survival responded to temperature and RH and potentially to EP; the secondary viral survival responded to temperature and potentially to RH. In both phases, survival of the virus was not significantly affected by AH. These findings suggest that long-distance transmission of airborne virus is more likely to occur at 20°C than at 10°C or 30°C and that current Gumboro vaccination by wet aerosolization in poultry industry is not very effective due to the fast initial decay.
    Combining fluidized activated carbon with weak alternating electric fields for disinfection
    Racyte, J. ; Sharabati, J. ; Paulitsch-Fuchs, A.H. ; Yntema, D.R. ; Mayer, M.J.J. ; Bruning, H. ; Rijnaarts, H.H.M. - \ 2011
    Carbon 49 (2011)15. - ISSN 0008-6223 - p. 5321 - 5328.
    advanced oxidation processes - waste-water - escherichia-coli - electromagnetic-fields - electrochemical treatment - 3-dimensional electrodes - magnetic-field - bacteria - cells - inactivation
    This study presents fluidized bed electrodes as a new device for disinfection. In the fluidized bed electrodes system, granular activated carbon particles were suspended, and an alternating radio frequency electric field was applied over the suspended bed. Proof-of-principle studies with the luminescent non-pathogenic bacterium Escherichia coli YMc10 demonstrated that disinfection with fluidized bed electrodes requires both the presence of granular activated carbon particles and the application of radio frequency electric field. Disinfection was investigated at various frequencies in range from 80 to 200 kHz at electric field strength of 6 ± 0.5 V/cm during 6 h. The largest decrease of E. coli viable cell concentration in the liquid (from 108 to 106 CFU/mL) was obtained at an optimum frequency of 140 kHz. Possible mechanisms of this electromediated disinfection are discussed in the manuscript. The results are promising for development of a new disinfection process with fluidized bed electrodes.
    Estimation of the Likelihood of Fecal-Oral HEV Transmission Among Pigs
    Bouwknegt, M. ; Teunis, P.F.M. ; Frankena, K. ; Jong, M.C.M. de; Rode Husman, A.M. de - \ 2011
    Risk Analysis 31 (2011)6. - ISSN 0272-4332 - p. 940 - 950.
    hepatitis-e-virus - local grocery stores - rt-pcr assay - united-states - experimental-infection - livers sold - sows feces - swine - japan - inactivation
    Sources for human hepatitis E virus (HEV) infections of genotype 3 are largely unknown. Pigs are potential animal reservoirs for HEV. Intervention at pig farms may be desired when pigs are confirmed as a source for human infections, requiring knowledge about transmission routes. These routes are currently understudied. The current study aims to quantify the likelihood of pig feces in causing new HEV infections in pigs due to oral ingestion. We estimated the daily infection risk for pigs by modeling the fate of HEV in the fecal–oral (F–O) pathway. Using parameter values deemed most plausible by the authors based on current knowledge the daily risk of infection was 0.85 (95% interval: 0.03–1). The associated expected number of new infections per day was ~4 (2.5% limit 0.1, the 97% limit tending to infinity) compared to 0.7 observed in a transmission experiment with pigs, and the likelihood of feces causing the transmission approached 1. In alternative scenarios, F–O transmission of HEV was also very likely to cause new infections. By reducing the total value of all explanatory variables by 2 orders of magnitude, the expected numbers of newly infected pigs approached the observed number. The likelihood of F–O transmission decreased by decreasing parameter values, allowing for at most 94% of infections being caused by additional transmission routes. Nevertheless, in all scenarios F–O transmission was estimated to contribute to HEV transmission. Thus, despite the difficulty in infecting pigs with HEV via oral inoculation, the F–O route is likely to cause HEV transmission among pigs.
    Can qualitatively similar temperature-histories be obtained in different pilot HP units?
    Landfeld, A. ; Matser, A.M. ; Strohalm, J. ; Oey, I. ; Plancken, I. van der; Grauwet, T. ; Hendrickx, M. ; Moates, G. ; Furfaro, M.E. ; Waldron, K.W. ; Betz, M. ; Halama, R. ; Houska, M. - \ 2011
    Innovative Food Science and Emerging Technologies 12 (2011)3. - ISSN 1466-8564 - p. 226 - 234.
    high hydrostatic-pressure - inactivation - uniformity - design - foods
    An experimental protocol to harmonize the pressure and temperature-histories of model samples treated in different individual high pressure pilot units was developed. This protocol was based on the endpoint strategy. Step zero of this protocol consisted of an exploratory measurement of the pressure, temperature-history of the pressure transmitting medium in the different chambers without the use of a container. In steps one and two of the protocol, the temperature of a sample was measured, which was placed in a container. Two types of samples were considered, a pure water sample allowing free convection (step 1) and a viscous water-based system (using a water soluble thickener) preventing free convection in the sample container (step 2). The high pressure units differed primarily in pressure build-up and pressure release times. The suggested endpoint strategy enabled the minimization of differences in temperature-histories during the pressure holding phase. Pressure, temperature-histories measured in the different high pressure units and information on the inactivation kinetics of a-amylase based systems were used to compare the process impact of different pressure, temperature-histories on the enzyme inactivation. The differences in temperature-histories significantly influenced the degree of enzyme inactivation; in particular the temperature-histories during the pressure build-up phase substantially contributed to differences in residual enzyme activity.
    Comparing equivalent thermal, high pressure and pulsed electric field processes for mild pasteurization of orange juice. Part I: Impact on overall quality attributes
    Timmermans, R.A.H. ; Mastwijk, H.C. ; Knol, J.J. ; Quataert, M.C.J. ; Vervoort, L. ; Plancken, I. van der; Hendrickx, M.E. ; Matser, A.M. - \ 2011
    Innovative Food Science and Emerging Technologies 12 (2011)3. - ISSN 1466-8564 - p. 235 - 245.
    escherichia-coli o157-h7 - pectin methyl esterase - citrus juices - shelf-life - food preservation - inactivation - pectinesterase - storage - microorganisms - vegetables
    Mild heat pasteurization, high pressure processing (HP) and pulsed electric field (PEF) processing of freshly squeezed orange juice were comparatively evaluated examining their impact on microbial load and quality parameters immediately after processing and during two months of storage. Microbial counts for treated juices were reduced beyond detectable levels immediately after processing and up to 2 months of refrigerated storage. Quality parameters such as pH, dry matter content and brix were not significantly different when comparing juices immediately after treatment and were, for all treatments, constant during storage time. Quality parameters related to pectinmethylesterase (PME) inactivation, like cloud stability and viscosity, were dependent on the specific treatments that were applied. Mild heat pasteurization was found to result in the most stable orange juice. Results for HP are nearly comparable to PEF except on cloud degradation, where a lower degradation rate was found for HP. For PEF, residual enzyme activity was clearly responsible for changes in viscosity and cloud stability during storage.
    Isolation of highly heat-resistant Listeria monocytogenes variants by use of a kinetic modeling-based sampling scheme
    Boeijen, K.H. van; Francke, C. ; Moezelaar, H.R. ; Abee, T. ; Zwietering, M.H. - \ 2011
    Applied and Environmental Microbiology 77 (2011)8. - ISSN 0099-2240 - p. 2617 - 2624.
    high hydrostatic-pressure - escherichia-coli - pasteurized milk - gene-expression - ctsr regulator - stress - inactivation - scott - environments - populations
    Stable high-hydrostatic-pressure (HHP)-resistant Listeria monocytogenes LO28 variants were previously isolated and characterized. These HHP variants were also more resistant to heat. In addition, nonlinear heat inactivation kinetics pointed toward the existence of heat-resistant variants, although these could not be isolated so far. In this study, we used kinetic modeling of inactivation curves of two isolated HHP variants and their wild type, and this revealed that the probability of finding resistant variants should depend on the nature of the inactivation treatment and the time of exposure. At specific heat and HHP conditions, resistant LO28 and EGDe variants were indeed isolated. Resistant LO28 variants were even isolated after a heat inactivation at 72°C in milk, and these variants showed high resistance to standard pasteurization conditions. The increased resistance of part of the isolated LO28 and EGDe variants was due to mutations in their ctsR genes. For the variants whose ctsR genes and upstream regions were not altered, the mechanisms leading to increased resistance remain to be elucidated. This research showed the strength of kinetic modeling in unraveling the causes of nonlinear inactivation and facilitating the isolation of heat-resistant L. monocytogenes variants
    Modelling and controller design for a UV disinfection plant
    Mourik, S. van; Geurts, B.J. ; Zwart, H.J. ; Keesman, K.J. - \ 2010
    European Journal of Control 16 (2010)2. - ISSN 0947-3580 - p. 119 - 128.
    waste-water reuse - inactivation - agriculture - bacteria - reactors
    A mathematical model describing fluid flow and concentration dynamics of micro-organisms inside a UV photoreactor is developed. Using physical arguments and techniques from system theory, we approximate this model by a first order linear one. For this reduced model, we design a controller. The controller is tested on the original model as well as on the reduced model by numerical simulation. This showed only small differences in dynamics, which indicates that for the original model a classic controller with excellent properties can be designed
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