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M C te Giffel

Publications and source records attributed to M C te Giffel.

10 recordsLinked to original sources
PubMed2002

Prediction of the adherence, growth and release of microorganisms in production chains.

The aim of this study was to develop a mathematical model that describes the bacterial contamination of food as a result of adherence, growth and release of bacteria in process equipment. The model developed can be applied to control the bacterial quality of food products produced in process chains in which the final contamination of the product is governed by growth and heat-induced destruction of bacteria. To set up the model, experiments were carried out with a plate heat exchanger using milk inoculated with Streptococcus thermophilus. The growth rate of S. thermophilus in milk could be described accurately by the modified expanded model of Ratkowsky. The observed increase in the concentration of S. thermophilus in milk at the outlet of the plate heat exchanger could be described quantitatively by the model. To predict the contamination of the product, the model was integrated into NIZO-PCS (Process Chain Simulator). The results of computer simulations were validated by a number of measurements in a cheese factory. It turned out that the agreement between the measured and calculated concentrations of S. thermophilus was sufficient for the model to be used for predictions in industrial production chains.

Animals↗
PubMed2002

Bacterial spores in silage and raw milk.

Spore-forming bacteria can survive food-processing treatments. In the dairy industry, Bacillus and Clostridium species determine the shelf-life of a variety of heat-treated milk products, mainly if the level of post-process contamination is low. In order to minimize problems caused by bacterial spores in foods and food production processes a chain management approach, from raw materials, ingredients and environmental sources to final product storage conditions, is most effective. Silage is considered to be a significant source of contamination of raw milk with spores. PCR-RAPD fingerprinting and heat resistance studies of populations of aerobic spore-formers isolated from grass and maize silage and from raw milk confirmed this assumption. Prevention of outgrowth of aerobic spores in silage will contribute to reduction of the total spore load of raw milk. Therefore, it is important that the silage fermentation process is controlled. Application of cultures of lactic acid bacteria or chemical additives can aid silage fermentation and improve aerobic stability.

Aerobiosis↗
PubMed2000

Stepwise quantitative risk assessment as a tool for characterization of microbiological food safety.

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.

Cheese↗
PubMed1999

Validation of predictive models describing the growth of Listeria monocytogenes.

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.

Animals↗
PubMed1998

[Isolation, identification and characterization of Bacillus cereus in the dairy industry].

In order to determine the major contamination sources of milk with (psychrotrophic) Bacillus cereus, the incidence of vegetative cells and spores of B. cereus on dairy farms, at two dairy processing plants and in pasteurized milk in household refrigerators was investigated. On dairy farms the major contamination sources were soil and faeces. In winter, when the cows were housed, used bedding probably also participates in this contamination route. The udder will be contaminated, finally resulting in the presence of B. cereus in raw milk. The organism could be detected in 35% of the raw milk samples analyzed. During processing, an increase in the percentage of positive samples was observed. These results suggest that B. cereus can be introduced via sources other than raw milk; equipment may play an important role in this. Biochemical and molecular typing showed that selection of strains takes place in the milk production chain. It was demonstrated that some types were found in the raw milk, during processing and in the end products, indicating that raw milk is an important source of contamination. Other types could only be detected after the pasteurization step in the production process supporting the assumption that additional contamination occurs during processing. If stored under proper conditions, maximum storage temperature 7 degrees C, and consumed within the expiration date, the levels of B. cereus in pasteurized milk will, in general, not exceed 10(5) per ml and cause no problems for healthy adults.

Animals↗
PubMed1997

Discrimination between Bacillus cereus and Bacillus thuringiensis using specific DNA probes based on variable regions of 16S rRNA.

Identification of Bacillus cereus and differentiation between B. cereus and closely related species are currently based on biochemical tests. The main problem is to discriminate between B. cereus and B. thuringiensis. Sequencing part of the 16S rRNA showed that several B. cereus isolates present in food and involved in food poisoning, confirmed according to the classical biochemical methods, were in fact B. thuringiensis. As this organism is the most commonly used microbial insecticide worldwide, the results of this study emphasize the need for accurate identification methods and for careful screening of strains for use as insecticides. Therefore, specific DNA probes based on the variable region VI of 16S rRNA of B. cereus and B. thuringiensis were designed. The probes were used in hybridization experiments with the variable region amplified using the polymerase chain reaction. In this way, a rapid and sensitive method was developed to distinguish B. cereus and B. thuringiensis.

Bacillus cereus↗
PubMed1997

Optimization of haemolysis in enhanced haemolysis agar (EHA)--a selective medium for the isolation of Listeria monocytogenes.

The presence of Listeria monocytogenes in enrichment media can be masked by faster growth of other Listeria spp. Therefore, enhanced haemolysis agar (EHA) is a good alternative for another isolation media, because the presence of a few L. monocytogenes colonies can be detected in a majority of colonies of other listeriae on the basis of haemolysis. In this study the haemolysis reaction in EHA was optimized. In a collaborative study using reference samples, no significant differences in counts on EHA, Palcam and Oxford agar were shown.

Agar↗
PubMed1996

Listeria species in domestic environments.

Using a direct isolation method Listeria spp. were detected in 101 (47.4%) of 213 houses investigated. L. monocytogenes was present in 45 houses (21.1%). Listeria spp. occurred at all sampling sites. Dish-cloths (37%) and surface samples round the drain in the bathroom (27.2%) were most frequently contaminated. Highest numbers (c. 10(4) c.f.u./object) were found in dish-cloths and washing-up brushes. Lower levels (up to 10(3) c.f.u./object) were obtained from kitchen sinks, refrigerator vegetable compartment samples and tooth brushes. In total, 132 isolations of Listeria spp. were made from 871 samples. L. innocua (53%) and L. monocytogenes (41%) were the predominant species in the positive samples. Other Listeria spp. were found in only 6% of the positive samples.

Environmental Microbiology↗
PubMed1996

Confirmation and identification of Listeria spp.

All confirmation and identification methods used in this study can be used for the screening of suspected colonies on isolation media for Listeria spp. In traditional enrichment procedures the Microscreen Listeria latex test gives fast results. The DNA probes (Accuprobe and Gene-Trak) are very specific in detecting Listeria monocytogenes. For identification of Listeria spp. both tests (API and Micro-ID) performed equally well. Preference may be given to the API test, since differentiation of L. monocytogenes from L. innocua is based on the absence of arylamidase, through which tests for haemolytic activity and/or CAMP reactions can be omitted. However, the use of Enhanced Haemolysis Agar as isolation medium makes further testing essentially superfluous, since L. monocytogenes strains can be differentiated from L. innocua.

DNA Probes↗