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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    Induction of satiation via aroma in dairy products
    Ruijschop, R. ; Boelrijk, A.E.M. ; Giffel, M.C. te; Graaf, C. de; Westerterp-Plantenga, M.S. - \ 2009
    Australian Journal of Dairy Technology 64 (2009)1. - ISSN 0004-9433 - p. 50 - 53.
    body-weight loss - flavor perception - energy-intake - food-intake - release - humans - satiety - maintenance - orthonasal - viscosity
    Sensory satiation is probably one of the most important factors in meal termination. In this paper, the use of aromas to induce satiation via dairy products is illustrated by means of two examples: the use of organic acids, obtained by fermentation; and altering the extent of retro-nasal aroma release. In a double-blind placebo-controlled randomised cross-over preload-test meal design, it was demonstrated that a dairy beverage fermented with propionic acid bacteria was perceived as more satiating than a non-fermented equivalent dairy beverage. Satiety-inducing effects lasted up to 50 min. However, ad libitum energy intake was not reduced in the time frame tested. Another approach is to increase satiation by making use of differences in retro-nasal aroma release profiles. It is known that the physical structure of a food product is important for the extent of retro-nasal aroma release, i.e. solid foods generate a longer retro-nasal aroma release compared to liquid foods. This is possibly also related to satiation. Using olfactometry, aroma stimuli can be administered separately from other stimuli, such as different ingredients, textures and tastes. Hence, the relative importance of aroma stimuli apart from other stimuli on satiation mechanisms can be investigated. In a double-blind placebo-controlled randomised cross-over full factorial design, it was shown that perceived satiation can be increased by altering the extent of aroma release during consumption of a liquid dairy product
    Contamination of raw milk with aerobic bacterial spores via the milking equipment
    Driehuis, F. ; Vissers, M.M.M. ; Slaghuis, B.A. ; Giffel, M.C. te - \ 2008
    In: Proceedings of the International Symposium on advances in milking, Cork, Ireland, 10 - 12 April, 2007. - Cork, Ireland : Teagasc - p. 119 - 120.
    Minimizing the level of Bacillus cereus spores in farm tank milk
    Vissers, M.M.M. ; Giffel, M.C.T. ; Driehuis, F. ; Jong, P. de; Lankveld, J.M.G. - \ 2007
    Journal of Dairy Science 90 (2007)7. - ISSN 0022-0302 - p. 3286 - 3293.
    psychrotrophic bacillus - raw-milk - pasteurized milk - contamination
    In a year-long survey on 24 Dutch farms, Bacillus cereus spore concentrations were measured in farm tank milk (FTM), feces, bedding material, mixed grass and corn silage, and soil from the pasture. The aim of this study was to determine, in practice, factors affecting the concentration of B. cereus spores in FTM throughout the year. In addition, the results of the survey were used in combination with a previously published modeling study to determine requirements for a strategy to control B. cereus spore concentrations in FTM below the MSL of 3 log(10) spores/L. The B. cereus spore concentration in FTM was 1.2 +/- 0.05 log(10) spores/L and in none of samples was the concentration above the MSL. The spore concentration in soil (4.9 +/- 0.04 log(10) spores/g) was more than 100-fold higher than the concentration in feces (2.2 +/- 0.05 log(10) spores/g), bedding material (2.8 +/- 0.07 loglo spores/g), and mixed silage (2.4 +/- 0.07 log(10) spores/g). The spore concentration in FTM increased between July and September compared with the rest of the year (0.5 +/- 0.02 log(10) spores/L difference). In this period, comparable increases of the concentrations in feces (0.4 +/- 0.03 loglo spores/g), bedding material (0.5 +/- 0.05 log(10) spores/g), and mixed silage (0.4 +/- 0.05 log(10) spores/g) were found. The increased B. cereus spore concentration in FTM was not related to the grazing of cows. Significant correlations were found between the spore concentrations in FTM and feces (r = 0.51) and in feces and mixed silage (r = 0.43) when the cows grazed. The increased concentrations during summer could be explained by an increased growth of B. cereus due to the higher temperatures. We concluded that year-round B. cereus spores were predominantly transmitted from feeds, via feces, to FTM. Farmers should take measures that minimize the transmission of spores via this route by ensuring low initial contamination levels in the feeds (
    Predictive modeling of Bacillus cereus spores in farm tank milk during grazing and housing periods
    Vissers, M.M.M. ; Giffel, M.C.T. ; Driehuis, F. ; Jong, P. de; Lankveld, J.M.G. - \ 2007
    Journal of Dairy Science 90 (2007)1. - ISSN 0022-0302 - p. 281 - 292.
    pasteurized milk - psychrotrophic bacillus - raw-milk - contamination - food
    The shelf life of pasteurized dairy products depends partly on the concentration of Bacillus cereus spores in raw milk. Based on a translation of contamination pathways into chains of unit-operations, 2 simulation models were developed to quantitatively identify factors that have the greatest effect on the spore concentration in milk. In addition, the models can be used to determine the reduction in concentration that could be achieved via measures at the farm level. One model predicts the concentration when soil is the source of spores, most relevant during grazing of cows. The other model predicts the concentration when feed is the main source of spores, most relevant during housing of cows. It was estimated that when teats are contaminated with soil, 33% of the farm tank milk (FTM) contains more than 3 log(10) spores/L of milk. When feed is the main source, this is only 2%. Based on the predicted spore concentrations in FTM, we calculated that the average spore concentration in raw milk stored at the dairy processor during the grazing period is 3.5 log(10) spores/L of milk and during the housing period is 2.1 log(10) spores/L. It was estimated that during the grazing period a 99% reduction could be achieved if all farms minimize the soil contamination of teats and teat cleaning is optimized. During housing, reduction of the concentration by 60% should be feasible by ensuring spore concentrations in feed below 3 log(10) spores/g and a pH of the ration offered to the cows below 5. Implementation of these measures at the farm level ensures that the concentration of B. cereus spores in raw milk never exceeds 3 log(10) spores/L.
    Short communication: quantification of the transmission of microorganisms to milk via dirt attached to the exterior of teats
    Vissers, M.M.M. ; Driehuis, F. ; Giffel, M.C.T. ; Jong, P. de; Lankveld, J.M.G. - \ 2007
    Journal of Dairy Science 90 (2007)8. - ISSN 0022-0302 - p. 3579 - 3582.
    butyric-acid bacteria - farm tank milk - raw-milk - risk-assessment - spores - contamination
    Pathogens and spoilage microorganisms can be transmitted to milk via dirt (e.g., feces, bedding material, soil, or a combination of these) attached to the exterior of the cows¿ teats. To determine the relevance of this pathway and to perform quantitative microbial risk analysis of the microbial contamination of farm tank milk (FTM), it is important to know the amount of dirt transmitted to milk via the exterior of teats. In this study at 11 randomly selected Dutch farms the amount of dirt transmitted to milk via the exterior of teats is determined using spores of mesophilic aerobic bacteria as a marker for transmitted dirt. The amount of transmitted dirt to milk varied among farms from 3 to 300 mg/L, with an average of 59 mg/L. The usefulness of the data for microbial risk analyses is briefly illustrated using the contamination of FTM with spores of butyric acid bacteria as a case study. In a similar way the data can be used to identify measures to control the contamination of FTM with other microorganisms or chemical residues.
    Minimizing the level of butyric acid bacteria spores in farm tank milk
    Vissers, M.M.M. ; Driehuis, F. ; Giffel, M.C.T. ; Jong, P. de; Lankveld, J.M.G. - \ 2007
    Journal of Dairy Science 90 (2007)7. - ISSN 0022-0302 - p. 3278 - 3285.
    clostridium-tyrobutyricum - aerobic deterioration - silage
    A year-long survey of 24 dairy farms was conducted to determine the effects of farm management on the concentrations of butyric acid bacteria (BAB) spores in farm tank milk (FTM). The results were used to validate a control strategy derived from model simulations. The BAB spore concentrations were measured in samples of FTM, feces, bedding material, mixed corn and grass silage fed to cows in the barn, and soil. In addition, a questionnaire was used to gather farm management information such as bedding material used and teat cleaning method applied. The average BAB spore concentration in FTM was 2.7 log(10) spores/L, and 33% of the FTM samples exceeded a concentration of 3 log(10) spores/L. Control of the average spore concentration in mixed silage fed was the only aspect of farm management that was significantly related to the concentration of BAB spores in FTM. Farms that fed mixed silage with the lowest average BAB spore concentrations (3.4 log(10) spores/g) produced FTM with the lowest average concentration (2.1 log(10) spores/L). The efficiency of farm management in controlling the BAB spore concentration in FTM depended to a large extent on the ability of farmers to prevent incidents with elevated BAB spore concentrations in mixed silage (>5 log(10) spores/g) and not on the average BAB spore concentration in mixed silage across the year. The survey showed that farmers should aim for a concentration in mixed silage of less than 3 loglo spores/g and should prevent the concentration from exceeding 5 log(10) spores/g to ensure a concentration in FTM of less than 3 loglo spores/L. These results correspond with the previously reported model simulations.
    Concentrations of butyric acid bacteria spores in silage and relationships with aerobic deterioration
    Vissers, M.M.M. ; Driehuis, F. ; Giffel, M.C.T. ; Jong, P. de; Lankveld, J.M.G. - \ 2007
    Journal of Dairy Science 90 (2007)2. - ISSN 0022-0302 - p. 928 - 936.
    clostridium-tyrobutyricum - grass-silage - growth
    Germination and growth of spores of butyric acid bacteria ( BAB) may cause severe defects in semihard cheeses. Silage is the main source of BAB spores in cheese milk. The objectives of the study were to determine the significance of grass silages and corn silages as sources of BAB spores and to investigate the relationships between high concentrations of BAB spores in corn silage and aerobic deterioration. In the first survey, samples were taken from various locations in silos containing grass and corn silages and from mixed silages in the ration offered to the cows on 21 farms. We demonstrated that the quantity of BAB spores consumed by cows was determined by a small fraction of silage with a high concentration of spores ( above 5 log(10) BAB/g). High concentrations were most often found in corn silage within areas with visible molds ( 69% of the samples). Areas with visible molds in grass silage and surface layers of corn silage contained, respectively, 21 and 19% of the cases of concentrations above 5 log10 BAB spores/g. Based on these results, we concluded that currently in the Netherlands, corn silage is a more important source of BAB than is grass silage. In a second survey, 8 corn silages were divided into 16 sections and each section was studied in detail. High concentrations of BAB spores were found in only the top 50 cm of these 8 silages. Elevated concentrations of BAB spores were associated with different signs of aerobic deterioration. In 13% of the sections in corn silage with more than 5 log10 yeasts and molds/g, more than 5 log10 BAB spores/g were found. Sections with a temperature of more than 5 C above ambient temperature contained, in 21% of the cases, more than 5 log10 BAB spores/g. Concentrations above 5 log10 BAB spores/g were measured in 50% of the sections with a pH above 4.4. All sections with a pH above 4.4 also showed a temperature that was more than 5 C above ambient temperature and a concentration of yeasts and molds above 5 log10 cfu/g. Based on these results, we postulated that high concentrations of BAB spores in corn silage are the result of oxygen penetration into the silage, resulting in aerobic deterioration and the formation of anaerobic niches with an increased pH just below the surface. Growth of BAB in these anaerobic niches with an increased pH caused the locally high concentrations of BAB in corn silage.
    Modeling to control spores in raw milk
    Vissers, M. - \ 2007
    Wageningen University. Promotor(en): J.M.G. Lankveld, co-promotor(en): M.C. te Giffel; P. de Jong. - [S.l.] : S.n. - ISBN 9789085046738 - 143
    rauwe melk - bacteriële sporen - boterzuurbacteriën - bacillus cereus - voedselbesmetting - microbiële besmetting - melkhygiëne - zuivelhygiëne - simulatiemodellen - raw milk - bacterial spores - butyric acid bacteria - bacillus cereus - food contamination - microbial contamination - milk hygiene - dairy hygiene - simulation models
    A modeling approach was used to identify measures at the farm that reduce transmission of microorganisms to raw milk. Butyric acid bacteria (BAB) and Bacillus cereus were used as case-studies. Minimizing the concentration of BAB spores in raw milk is important to prevent late-blowing of Gouda-type cheeses. Reducing the concentration of B. cereus spores in raw milk increases the shelf life of refrigerated pasteurized dairy products.

    First, predictive models were developed based on a translation of contamination pathways into chains of unit-operations. Via simulations, strategies were identified to control spore concentrations in farm tank milk (FTM)below 1,000 spores/L.Subsequently, the identified strategies were validated using data from a year-long field survey held at 24 Dutch farms.

    The results of this study show that mathematical modeling is very useful to identify effective measures to reduce the contamination of FTM with spores. The control strategies derived using model simulations were in agreement with results from the field survey. The following general conclusions were drawn:

    ·       To minimize the concentration of BAB spores in FTM, it is by far most important to prevent growth of BAB in grass- and corn-silage. Farmers should aim for a concentration in grass- and corn-silage fed to cowsbelow 1,000 spores/g. To achieve this, it is essential to prevent oxygen penetration into the silage silo and to remove molded and deteriorated silage from the ration fed to the cows. Measures aimed at other parts of the contamination pathway, such as teat cleaning prior to milking, are much less effective.

    ·       The concentration of B. cereus spores in FTM isnormally below 1,000 spores/L.During housing and pasturing spores of B. cereus in FTM originate from feeds. Two critical factors could lead to concentrations above 1,000 spores/L. Firstly, the contamination teats with soil is a high risk because soil can contain high concentrations of B. cereus spores. Secondly, build-up of B. cereus in improperly cleaned milking equipment could lead to high spore concentrations in FTM.

    ·       Implementation of the measures identified in this study could make late-blowing of Gouda-type cheeses a rare incident and prolong the shelf life of refrigerated pasteurized consumer milk by approximately 10%.


    A modeling approach was used to identify measures at the farm that reduce transmission of microorganisms to raw milk. Spores of butyric acid bacteria (BAB) and Bacillus cereus were used as case-studies because of their relevance for the Dutch dairy industry..The following general conclusions were drawn:

    ·       To minimize the concentration of BAB spores in FTM, it is by far most important to prevent growth of BAB in grass- and corn-silage. Farmers should aim for a concentration in grass- and corn-silage fed to cowsbelow 1,000 spores/g. To achieve this, it is essential to prevent oxygen penetration into the silage silo and to remove molded and deteriorated silage from the ration fed to the cows. Measures aimed at other parts of the contamination pathway, such as teat cleaning prior to milking, are much less effective.

    ·       The concentration of B. cereus spores in FTM isnormally below 1,000 spores/L.During housing and pasturing spores of B. cereus in FTM originate from feeds. Two critical factors could lead to concentrations above 1,000 spores/L. Firstly, the contamination teats with soil is a high risk because soil can contain high concentrations of B. cereus spores. Secondly, build-up of B. cereus in improperly cleaned milking equipment could lead to high spore concentrations in FTM.

    ·       Implementation of the measures identified in this study could make late-blowing of Gouda-type cheeses a rare incident and prolong the shelf life of refrigerated pasteurized consumer milk by approximately 10%.

    Improving farm management by modeling the contamination of farm tank milk with butyric acid bacteria
    Vissers, M.M.M. ; Driehuis, F. ; Giffel, M.C. te; Jong, P. de; Lankveld, J.M.G. - \ 2006
    Journal of Dairy Science 89 (2006)3. - ISSN 0022-0302 - p. 850 - 858.
    clostridium-tyrobutyricum - bacillus-cereus - grass-silage - cheese - growth - spores - food
    Control of contamination of farm tank milk (FTM) with the spore-forming butyric acid bacteria (BAB) is important to prevent the late-blowing defect in semi-hard cheeses. The risk of late blowing can be decreased via control of the contamination level of FTM with BAB. A modeling approach was applied to identify an effective control strategy at the farm level. The simulation model developed was based on a translation of the contamination pathway into a chain of unit operations. Using various simulations, the effects of factors related to feed quality, feed management, cattlehouse hygiene, and milking practices on the contamination level of FTM were evaluated. Contamination level of silage was found to be the most important factor. When silage contains on average less than 3 log(10) BAB/g, a basic pretreatment of udder teats before milking (similar to 75% removal of attached spores) is sufficient to assure an FTM contamination level below 1 BAB/mL. When silage contains more than 5 log(10) BAB/g, it should not be fed, because it then becomes almost impossible to assure an FTM contamination level below 1 BAB/mL. Measures aimed at improving cattlehouse hygiene, the contamination via soil, and the contamination level of other feeds contribute only marginally to the control of the contamination of FTM with BAB. Application of the modeling methodology could be beneficial for the control of the contamination of FTM with other microorganisms such as Bacillus cereus.
    Microbiële kwaliteit voorspellen
    Vissers, M. ; Straver, J.M. ; Giffel, M.C. te; Jong, P. de; Zwietering, M.H. ; Boekel, M.A.J.S. van; Lankveld, J.M.G. - \ 2004
    Voedingsmiddelentechnologie 37 (2004)21. - ISSN 0042-7934 - p. 16 - 18.
    voedingsmiddelen - microbiologie - modellen - computersimulatie - simulatiemodellen - informatiesystemen - analyse - toepassingen - kwaliteit - foods - microbiology - models - computer simulation - simulation models - information systems - analysis - applications - quality
    Microbial quality and safety of foodstuffs can be improved by reducing the microbial load of the raw materials. Especially in products in which microbial spoilage is caused by sporeforming bacteria this can be the only solution. Combining existing datasets, expert knowledge and quantitative modeling techniques in a smart way have increased insight in the contamination of raw milk with the sporeforming butyric acid bacteria and Bacillus cereus. In this way the effect of various control points was quantified enabling a objective comparison of control points. Based on this information uncertainty about the true effect of various measures can be clarified and more effective measures can be identified
    Cobalt as a tracer for estimation of residues in milk after application of automatic teat cleaning systems
    Slaghuis, B.A. ; Ferwerda, R.T. ; Giffel, M.C. te; Ellen, G. - \ 2004
    In: Automatic milking - a better understanding Wageningen : Wageningen Academic - ISBN 9789076998381 - p. 119 - 120.
    Robotic milking and free fatty acids
    Slaghuis, B.A. ; Bos, C.H. ; Jong, O. de; Tudos, A.J. ; Giffel, M.C. te; Koning, C.J.A.M. de - \ 2004
    In: Automatic milking - a better understanding: The International Symposium on Automatic Milking, Lelystad March 24-26 2004 Wageningen : Wageningen Academic - ISBN 9789076998381 - p. 341 - 347.
    Use of Cobalt as tracer for detection of chemical residues during the milking and cleaning process
    Slaghuis, B.A. ; Ferwerda-van Zonneveld, R.T. ; Giffel, M.C. te; Ellen, G. - \ 2003
    In: Proceedings of the 54th Annual meeting of the European Association for Animal Production (EAAP), Rome, Italy, 2003-08-30/ 2003-09-03. - Wageningen : Wageningen Academic Publishers - ISBN 9789076998206 - p. 123 - 123.
    The effect of a combined intramammary and intramuscular treatment of mastitis on excretion of antibiotics in milk
    Poelarends, J.J. ; Hogeveen, H. ; Giffel, M. te - \ 2001
    In: Proceedings of the 2nd international symposium on mastitis and milk quallity, Vancouver BC Canada 13-15 September 2001. - [S.l.] : [s.n.], 2001 - p. 269 - 273.
    Bacillus cereus in milk and milk products : Advances in detection, typing and epidemiology
    Giffel, M.C. te; Beumer, R.R. ; Christansson, A. ; Griffiths, M.W. - \ 2000
    Bulletin / International Dairy Federation 357 (2000). - ISSN 0259-8434 - p. 47 - 54.
    Stepwise quantitative risk assessment as a tool for characterization of microbiological food safety
    Gerwen, S.J.C. van; Giffel, M.C. te; Riet, K. van 't; Beumer, R.R. ; Zwietering, M.H. - \ 2000
    Journal of Applied Microbiology 88 (2000). - ISSN 1364-5072 - p. 938 - 951.
    This paper describes a system for the microbiological quantitative risk assessment for food products and their production processes. The system applies a stepwise risk assessment, allowing the main problems to be addressed before focusing on less important problems. First, risks are assessed broadly, using order of magnitude estimates. Characteristic numbers are used to quantitatively characterize microbial behaviour during the production process. These numbers help to highlight the major risk- determining phenomena, and to find negligible aspects. Second, the risk- determining phenomena are studied in more detail. Both general and/or specific models can be used for this and varying situations can be simulated to quantitatively describe the risk-determining phenomena. Third, even more detailed studies can be performed where necessary, for instance by using stochastic variables. The system for quantitative risk assessment has been implemented as a decision supporting expert system called SIEFE: Stepwise and Interactive Evaluation of Food safety by an Expert System. SIEFE performs bacterial risk assessments in a structured manner, using various information sources. Because all steps are transparent, every step can easily be scrutinized. In the current study the effectiveness of SIEFE is shown for a cheese spread. With this product, quantitative data concerning the major risk-determining factors were not completely available to carry out a full detailed assessment. However, this did not necessarily hamper adequate risk estimation. Using ranges of values instead helped identifying the quantitatively most important parameters and the magnitude of their impact. This example shows that SIEFE provides quantitative insights into production processes and their risk-determining factors to both risk assessors and decision makers, and highlights critical gaps in knowledge.
    Isolatie en bevestiging van Bacillus subtilis uit vlaaien en gevulde snacks
    Groezen, J.H.J. van; Giffel, M.C. te; Vermunt, A.E.M. - \ 1999
    De Ware(n)-Chemicus (1999). - ISSN 0166-8838
    Bacillus cereus : a review
    Giffel, M.C. te; Beumer, R.R. - \ 1999
    The Journal of Food Technology in Africa 4 (1999)1. - p. 7 - 13.
    Application of predictive models as a tool in the food industry
    Giffel, M.C. te; Jong, P. de; Zwietering, M.H. - \ 1999
    New Food 2 (1999)2. - ISSN 1461-4642 - p. 38 - 41.
    Validation of predictive models describing the growth of Listeria monocytogenes
    Giffel, M.C. te; Zwietering, M.H. - \ 1999
    International Journal of Food Microbiology 46 (1999)2. - ISSN 0168-1605 - p. 135 - 149.
    In this study, predictions for growth rate of Listeria on food products were evaluated by both general applicable models and specific growth models. Literature values, obtained from a large number of publications, for growth rates in/on a variety of foods were compared by graphical and mathematical analysis with predictions given by various models. Apart for the great advantage of being generally applicable, the general models performed best. However, only small differences between the various models were observed. Model predictions were accurate within a factor of about two to four, depending on the type of product. The predictions should therefore not be considered as absolute; it is important to understand the limitations of the performance of models. All results and all assumptions should be criticised, but in many cases the accuracy will be sufficient to use these types of models as a tool in management decisions.
    Enterobacteriaceae, Coliforms and Escherichia coli
    Beumer, R.R. ; Giffel, M.C. te; Griffioen, A.G.E. - \ 1999
    In: Encyclopedia of food microbiology - p. 244 - 249.
    Pathogens in domestic kitchens: facts and fiction
    Beumer, R.R. ; Giffel, M.C. te - \ 1999
    In: Food microbiology and food safety into the next millennium : proceedings of the 17th international conference of the international committee on food microbiology and hygiene (ICFMH), Veldhoven, The Netherlands, 12-17 September 1999 / A.C.J. Tuijtelaars, R.A. Samson, F.M. Rombouts, S. Notermans. Zeist : Foundation Food Micro 99, 1999 - p. 345 - 347.
    Microbiële besmettingsbronnen in huishoudens
    Beumer, R.R. ; Giffel, M.C. te - \ 1999
    In: Ongenode gasten aan tafel: over voedselinfecties: een volksgezondheidsprobleem / Stasse-Wolthuis, M., van Binsbergen, J.J., Houten/Diegem : Bohn Stafleu van Loghum - p. 41 - 48.
    Listeria monocytogenes : A micro-organism of concern?
    Beumer, R.R. ; Giffel, M.C. te - \ 1999
    The Journal of Food Technology in Africa 4 (1999)1. - p. 14 - 17.
    Use of predictive models as a tool in food safety.
    Giffel, M.C. te; Zwietering, M.H. - \ 1998
    In: 3rd Conference in Food Microbiology, Luik, Belgium - p. 61 - 66.
    Modellen voldoende nauwkeurig voor praktijktoepassing.
    Giffel, M.C. te; Zwietering, M.H. - \ 1998
    Voedingsmiddelentechnologie (1998). - ISSN 0042-7934 - p. 27 - 31.
    Evaluation of predictive models describing the growth of Listeria monocytogenes.
    Giffel, M.C. te; Zwietering, M.H. - \ 1998
    In: 13th International Symposium on Problems of Listeriosis, Halifax, Nova Scotia, Canada - p. 24 - 24.
    Evaluation of predictive models describing the growth of Listeria monocytogenes.
    Giffel, M.C. te; Zwietering, M.H. - \ 1998
    In: Shelf life prediction for improved safety and quality of foods - p. 97 - 104.
    De pulsifier: een alternatief voor de stomacher bij het maken van primaire verdunningen van levensmiddelen bij het verrichten van kiemtellingen.
    Beumer, R.R. ; Galavazi, R. ; Diavatopoulos, T. ; Hemmelder, D.J. ; Giffel, M.C. te - \ 1998
    Voedingsmiddelentechnologie 31 (1998). - ISSN 0042-7934
    Isolatie, identificatie en karakterisering van Bacillus cereus in de zuivelindustrie.
    Giffel, M.C. te; Beumer, R.R. - \ 1998
    Tijdschrift voor Diergeneeskunde 123 (1998). - ISSN 0040-7453 - p. 628 - 632.
    Listeria monocytogenes: growth and survival of strains isolated from meat environments on various surfaces.
    Beumer, R.R. ; Giffel, M.C. te - \ 1998
    In: 13th International Symposium on Problems of Listeriosis, Halifax, Nova Scotia, Canada - p. 23 - 23.
    Listeria spp. in domestic environments.
    Beumer, R.R. ; Giffel, M.C. te - \ 1998
    In: 13th International Symposium on Problems of Listeriosis, Halifax, Nova Scotia, Canada - p. 23 - 23.
    Effect of the application of the lactoperoxidase system in feed on the colonization of Campylobacter jejuni in chickens.
    Beumer, R.R. ; Giffel, M.C. te - \ 1998
    In: Campylobacter, Helicobacter and related organisms: Proceedings of the 9th International Workshop, Cape Town, South Africa - p. 418 - 418.
    Evaluation of the pulsifier for preparation of food homogenates.
    Beumer, R.R. ; Galavazi, R. ; Diavatopoulos, T. ; Hemmelder, D.J. ; Giffel, M.C. te - \ 1998
    De Ware(n)-Chemicus 28 (1998). - ISSN 0166-8838 - p. 82 - 82.
    Germination of bacterial spores during sample preparation.
    Giffel, M.C. te; Beumer, R.R. ; Rombouts, F.M. - \ 1998
    De Ware(n)-Chemicus 28 (1998). - ISSN 0166-8838 - p. 75 - 75.
    Isolation and characterization of Bacillus subtilis from bakery products.
    Giffel, M.C. te; Bleumink, B. ; Vermunt, A.E.M. ; Groezen, J.H.J. van - \ 1998
    De Ware(n)-Chemicus 28 (1998). - ISSN 0166-8838 - p. 74 - 74.
    Repeatability of teat swabbing and teat sweab results for spores of Bacillus cereus in relation to housing system.
    Slaghuis, B.A. ; Klungel, G.H. ; Giffel, M.C. te - \ 1998
    De Ware(n)-Chemicus 28 (1998). - ISSN 0166-8838 - p. 72 - 72.
    Occurrence and survival of verocytotoxin-producing Escherichia coli in raw cow's milk in The Netherlands.
    Heuvelink, A.E. ; Bleumink, B. ; Biggelaar, F.L.A.M. van den; Giffel, M.C. te; Beumer, R.R. ; Boer, E. de - \ 1998
    Journal of Food Protection 61 (1998). - ISSN 0362-028X - p. 1597 - 1601.
    Evaluation of predictive models describing the growth of Listeria monocytogenes.
    Giffel, M.C. te; Zwietering, M.H. - \ 1997
    In: Final Workshop Copernicus Project (CIPA-CT94-0120) Shelf-life prediction, Wageningen, NL - p. 68 - 75.
    Isolation and characterisation of Bacillus cereus from pasteurised milk in household refrigerators in the Netherlands.
    Giffel, M.C. te; Beumer, R.R. ; Granum, P.E. ; Rombouts, F.M. - \ 1997
    International Journal of Food Microbiology 34 (1997). - ISSN 0168-1605 - p. 307 - 318.
    Isolation and characterisation of Bacillus cereus from pasteurised milk in household refrigerators in The Netherlands.
    Giffel, M.C. te; Beumer, R.R. ; Granum, P.E. ; Rombouts, F.M. - \ 1997
    In: Symposium Toxins, University of East Anglia, Norwich, 1997, Society for Applied Bacteriology, Bedford, UK (1997) xi
    Discrimination between Bacillus cereus and Bacillus thuringiensis using specific DNA probes based on variable regions of 16S rRNA.
    Giffel, M.C. te; Beumer, R.R. ; Klijn, N. ; Wagendorp, A. ; Rombouts, F.M. - \ 1997
    FEMS Microbiology Letters 146 (1997). - ISSN 0378-1097 - p. 47 - 51.
    Discrimination between Bacillus cereus and Bacillus thuringiensis using specific DNA probes based on variable regions of 16S rRNA.
    Giffel, M.C. te; Beumer, R.R. ; Klijn, N. ; Wagendorp, A. ; Rombouts, F.M. - \ 1997
    In: FEMS International Conference 'Fundamental and Applied Aspect of Bacterial Spores (1997)
    The role of heat exchangers in the contamination of milk with Bacillus cereus in dairy processing plants.
    Giffel, M.C. te; Beumer, R.R. ; Langeveld, L.P.M. ; Rombouts, F.M. - \ 1997
    International Journal of Dairy Technology 50 (1997). - ISSN 1364-727X - p. 43 - 47.
    The role of heat exchangers in the contamination of milk with Bacillus cereus.
    Giffel, M.C. te; Beumer, R.R. ; Rombouts, F.M. - \ 1997
    In: World Congress on Food Hygiene, The Hague, NL - p. 297 - 297.
    Ontwikkeling DNA-probes voor onderscheid B. cereus en B.thuringiensis.
    Giffel, M.C. te; Beumer, R.R. - \ 1997
    Voedingsmiddelentechnologie 30 (1997)23. - ISSN 0042-7934 - p. 11 - 14.
    Use and validation of the gamma-model for prediction of pathogen growth to be used in HACCP and risk assessment.
    Giffel, M.C. te; Zwietering, M.H. - \ 1997
    In: 5th European Conference on Food Industry and Statistics, Versailles, France (1997) 15.1-15.9
    Isolation, identification and characterization of Bacillus cereus from the dairy environment
    Giffel, M. te - \ 1997
    Agricultural University. Promotor(en): F.M. Rombouts; R.R. Beumer. - S.l. : Te Giffel - ISBN 9789054856948 - 150
    melkproducten - zuivelindustrie - bacteriën - identificatie - milk products - dairy industry - bacteria - identification

    In this thesis the occurrence of Bacillus cereus in the milk production and processing environment was investigated. Isolates were identified biochemically and by DNA probes based on the variable regions of 16S rRNA. Further characterization was carried out using biochemical and molecular typing, in order to determine the major contamination sources of milk. Furthermore, properties in relation to carbohydrate utilization, growth at low temperatures and enterotoxin production were examined.

    B. cereus is important as food spoilage organism. In the present study the microorganism was isolated from food ingredients such as yeast, flour, cacoa, herbs and spices. B. cereus was also found in a wide variety of processed food products including bakery products, Chinese meals, pasta products, chocolate and meat products. In pasteurized milk and dairy products, B. cereus was frequently present and it is well-known that it can be responsible for spoilage when post-heat- treatment contamination is absent.

    To enumerate spores in a sample, the most common procedure is to carry out a heat- activation treatment of 10 min at 80°C, followed by plating on a (selective) agar medium. To prevent germination of spores during sample preparation the time between the preparation of the primary dilution and heat-activation step should be less than 10 min and the temperature during the analysis should be as low as possible (e.g. by keeping dilutions in melting ice). After isolation, presumptive B. cereus are confirmed by biochemical tests, however, this may lead to incorrect identification. Several isolates, involved in food poisoning incidents, were shown to be B. thuringiensis, by sequencing part of the 16S rRNA. These results suggest that use of B. thuringiensis as insecticide may lead to foodborne infection or intoxication. To improve the confirmation procedure, we developed a specific and sensitive method, using DNA probes based on variable regions of the 16S rRNA, to differentiate between B. cereus and B. thuringiensis.

    On farms, B. cereus is introduced into raw milk by contamination of the udder with faeces, soil and, in winter, used bedding. In the dairy processing plants, additional contamination takes place via the equipment. Biochemical and growth characterization and molecular typing of isolates confirmed this and also showed that selection of strains occurs in the milk production and processing chain. Cleaning and disinfection will not eliminate all B. cereus in milking installations or heat exchangers, particularly not those adhering to surfaces of the equipment.

    Although only a few cases of milkborne infection and intoxication by B. cereus have been reported, most isolates were able to produce enterotoxin as determined by immunoblotting, cytotoxicity tests and PCR. However, if pasteurized milk is stored at
    7°C and consumed within the "best before" date, this will not cause any problems for healthy adults.

    Effect of pasturing on the incidence of Bacillus cereus spores in raw milk.
    Slaghuis, B.A. ; Giffel, M.C. te; Beumer, R.R. ; André, G. - \ 1997
    International Journal of Dairy Technology 7 (1997). - ISSN 1364-727X - p. 201 - 205.
    Influence of lactate and acetic acid on survival of Escherichia coli O157H7.
    Planken, E.M.J.E. ; Beumer, R.R. ; Giffel, M.C. te; Boer, Y. de - \ 1997
    In: World Congress on Food Hygiene, The Hague, NL - p. 200 - 200.
    A risk assessment study of Bacillus cereus present in pasteurized milk.
    Notermans, S. ; Dufrenne, J. ; Teunis, P. ; Beumer, R.R. ; Giffel, M.C. te; Peeters Weem, P. - \ 1997
    Food Microbiology 14 (1997). - ISSN 0740-0020 - p. 143 - 151.
    The effect of the lactoperoxidase system on Escherichia coli O157H7.
    Bleumink, E.B. ; Beumer, R.R. ; Giffel, M.C. te; Boer, E. de - \ 1997
    In: World Congress on Food Hygiene, The Hague, NL - p. 199 - 199.
    Optimization of haemolysis in enhanced haemolysis agar (EHA) - a selective medium for the isolation of Listeria monocytogenes.
    Beumer, R.R. ; Giffel, M.C. te; Cox, L.J. - \ 1997
    Letters in Applied Microbiology 24 (1997). - ISSN 0266-8254 - p. 421 - 425.
    A comparison of rapid methods for the detection of Listeria monocytogenes.
    Beumer, R.R. ; Giffel, M.C. te; Kok, M.T.C. ; Cox, L.J. ; Rombouts, F.M. - \ 1996
    Food australia 48 (1996)4. - ISSN 1032-5298 - p. 160 - 163.
    Op zoek naar L. monocytogenes.
    Beumer, R.R. ; Giffel, M.C. te - \ 1996
    Voedingsmiddelentechnologie 29 (1996)21. - ISSN 0042-7934 - p. 45 - 48.
    analyse - chemie - voedselbesmetting - voedselmicrobiologie - infectieziekten - listeria - analytische scheikunde - analysis - chemistry - food contamination - food microbiology - infectious diseases - listeria - analytical chemistry
    Een uiteenzetting van de factoren die van invloed zijn op de isolatie, de bevstiging en de identificatie van genoemde pathogene bacterie
    Isolation and characterization of Bacillus cereus at dairy factories.
    Giffel, M.C. te; Beumer, R.R. ; Bonestroo, M.H. - \ 1996
    In: Abstract 16th Int. Symp. IUMS-ICFMH Food Micro '96, Budapest, Hungary - p. 178 - 178.
    Occurrence and characterization of (psychrotrophic) Bacillus cereus on farms in The Netherlands.
    Giffel, M.C. te; Beumer, R.R. ; Slaghuis, B.A. ; Rombouts, F.M. - \ 1996
    In: Symp. on Bacteriological quality of raw milk, Wolfpassing, Austria - p. 40 - 45.
    Listeria monocytogenes in domestic environments.
    Beumer, R.R. ; Giffel, M.C. te - \ 1996
    In: Food Associated Pathogens, Uppsala, Sweden - p. 212 - 213.
    Sporicidal effect of disinfectants on Bacillus cereus spores isolated from the milk processing environment.
    Giffel, M.C. te; Beumer, R.R. ; Dam, W.F. van; Rombouts, F.M. - \ 1996
    In: Symp. on Bacteriological quality of raw milk, Wolfpassing, Austria - p. 167 - 168.
    Evidence for a further enterotoxin complex produced by Bacillus cereus.
    Granum, P.E. ; Andersson, A. ; Gayther, C. ; Giffel, M. te; Larsen, H. ; Lund, T. ; O'Sullivan, K. - \ 1996
    FEMS Microbiology Letters 141 (1996). - ISSN 0378-1097 - p. 145 - 149.
    Growth of Listeria monocytogenes on sliced cooked meat products.
    Beumer, R.R. ; Giffel, M.C. te; Boer, E. de; Rombouts, F.M. - \ 1996
    Food Microbiology 13 (1996). - ISSN 0740-0020 - p. 333 - 340.
    Listeria species in domestic environments.
    Beumer, R.R. ; Giffel, M.C. te; Spoorenberg, E. ; Rombouts, F.M. - \ 1996
    Epidemiology and Infection 117 (1996)3. - ISSN 0950-2688 - p. 437 - 442.
    Incidence and characterization of Bacillus cereus in two dairy processing plants.
    Giffel, M.C. te; Beumer, R.R. ; Bonestroo, M.H. ; Rombouts, F.M. - \ 1996
    Netherlands Milk and Dairy Journal 50 (1996). - ISSN 0028-209X - p. 479 - 492.
    Confirmation and identification of Listeria spp.
    Beumer, R.R. ; Giffel, M.C. te; Kok, M.T.C. ; Rombouts, F.M. - \ 1996
    Letters in Applied Microbiology 22 (1996). - ISSN 0266-8254 - p. 448 - 452.
    Incidence of Bacillus cereus and Bacillus subtilis in foods in the Netherlands.
    Giffel, M.C. te; Beumer, R.R. ; Leijendekkers, S. ; Rombouts, F.M. - \ 1996
    Food Microbiology 13 (1996). - ISSN 0740-0020 - p. 53 - 58.
    The effect of acriflavine and nalidixic acid on the growth of Listeria spp. in enrichment media.
    Beumer, R.R. ; Giffel, M.C. te; Anthonie, S.V.R. ; Cox, L.J. - \ 1996
    Food Microbiology 13 (1996). - ISSN 0740-0020 - p. 137 - 148.
    Sporicidal effect of disinfectants on Bacillus cereus isolated from the milk processing environment.
    Giffel, M. te; Beumer, R.R. ; Dam, W.F. van; Slaghuis, B.A. - \ 1995
    International Biodeterioration and Biodegradation 36 (1995). - ISSN 0964-8305 - p. 421 - 430.
    Growth of Listeria monocytogenes on sliced cooked meat products.
    Boer, E. de; Beumer, R.R. ; Asselt, A. van; Giffel, M.C. te - \ 1995
    In: Proc. 12th Int. Symp. on Problems of Listeriosis, Perth, Western Australia. Promaco Conventions Pty Ltd, Canning Bridge, Western Australia - p. 253 - 256.
    Characteristics of some psychrotrophic Bacillus cereus isolates.
    Dufrenne, J. ; Bijwaard, M. ; Giffel, M. te; Beumer, R. ; Notermans, S. - \ 1995
    International Journal of Food Microbiology 27 (1995). - ISSN 0168-1605 - p. 175 - 183.
    Occurrence and characterization of (psychrotrophic) Bacillus cereus on farms in the Netherlands.
    Giffel, M.C. te; Beumer, R.R. ; Slaghuis, B.A. ; Rombouts, F.M. - \ 1995
    Netherlands Milk and Dairy Journal 49 (1995). - ISSN 0028-209X - p. 125 - 138.
    Germination of bacterial spores during sample preparation.
    Giffel, M.C. te; Beumer, R.R. ; Hoekstra, J. ; Rombouts, F.M. - \ 1995
    Food Microbiology 12 (1995). - ISSN 0740-0020 - p. 327 - 332.
    Effect of exogenous betaine and carnitine on the growth of Listeria in a minimal medium.
    Giffel, M.C. te; Beumer, R.R. ; Cox, L.J. ; Rombouts, F.M. ; Abee, T. - \ 1995
    In: Proc. 12th Int. Symp. on Problems of Listeriosis, Perth, Western Australia. Promaco Conventions Pty Ltd, Canning Bridge, Western Australia - p. 123 - 127.
    Sporicidal effect of disinfectants on Bacillus cereus spores isolated from the milk processing environment.
    Giffel, M.C. te; Beumer, R.R. ; Dam, W.F. van; Rombouts, F.M. - \ 1995
    De Ware(n)-Chemicus 25 (1995). - ISSN 0166-8838 - p. 142 - 142.
    A comparison of (rapid) methods for the detection of Listeria monocytogenes.
    Beumer, R.R. ; Giffel, M.C. te; Kok, M.T.C. ; Cox, L.J. ; Rombouts, F.M. - \ 1995
    In: Proc. 12th Int. Symp. on Problems of Listeriosis, Perth, Western Australia. Promaco Conventions Pty Ltd, Canning Bridge, Western Australia - p. 53 - 56.
    Effect of exogenous proline, betaine, and carnitine on growth of Listeria monocytogenes in a minimal medium.
    Beumer, R.R. ; Giffel, M.C. te; Cox, L.J. ; Rombouts, F.M. ; Abee, T. - \ 1994
    Applied and Environmental Microbiology 60 (1994)4. - ISSN 0099-2240 - p. 1359 - 1363.
    Three Listeria monocytogenes strains isolated from food or food-processing environments were used to assess the response of this species to salinity in a chemically defined minimal medium. Growth in a minimal medium containing five essential amino acids and glucose as a carbon and energy source was comparable to growth in a rich medium (brain heart infusion broth). In the absence and presence of 3% NaCl the final cell numbers reached in minimal medium were 10(9) and 10(7) CFU/ml, respectively. Growth under the latter conditions could not be detected by spectrophotometry by measuring A660. Apparently, this technique was not suitable for these experiments since the detection level was > 10(7) CFU/ml. Exogenously added proline (10 mM), trimethylglycine (betaine) (1 mM), and beta-hydroxy-gamma-N-trimethyl aminobutyrate (carnitine) (1 mM) significantly stimulated growth under osmotic stress conditions in minimal medium at both 37 and 10 degrees C. Betaine and carnitine are present in foods derived from plants and animals, respectively. Therefore, these compounds can contribute significantly to growth of L. monocytogenes in various foods at high osmolarities.
    Detection of Bacillus cereus in environmental samples and milk on farms.
    Giffel, M.C. te; Beumer, R.R. ; Hoekstra, J. - \ 1993
    In: Summer Conf., Soc. Applied Bacteriology, Nottingham (1993)
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