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B01021: Challenging and validating Clostridium botulinum models for Food MicroModel

Wednesday 21 April 2004

This research project will develop predictive models for the growth of Clostridium botulinum in food and food-relevant model systems.

Study Duration : October 2000 to May 2002

Contractor : Central Science Laboratory (CSL)

Background

The development of predictive models for the growth of Clostridium botulinum in food and food-relevant model systems is essential for improved safety and the effective hazard identification and risk analysis that are required to be carried out by UK and EU laws.

C. botulinum has the potential to produce neurotoxins that can cause death of consumers after consumption of food in which the toxin has been formed. Therefore, it is one of the most severe forms of food poisoning and it is of continued concern to the food industry. Consumer demands for increasing varieties of minimally treated convenience foods with low levels of sugar and salt or preservatives may increase the potential for C. botulinum to grow.

The C. botulinum model represents the final part of the microorganisms studied in the Food MicroModel project. Selected growth models for proteolytic cocktails of C. botulinum strains were developed over a narrow range of conditions and limited validation studies of these models in food were carried out.

The development of predictive models for the growth of C. botulinum is important to establish the physiological behaviour of the food pathogens in food systems at any given composition and to anticipate potential effects on its ability to grow and form toxin.

The aim of this project was to develop predictive models for the growth of C. botulinum in food and food-relevant model systems.

Research Approach

Preparations of standardised and characterised spore crops of a variety of proteolytic strains of C. botulinum will be prepared.

Cocktails of proteolytic strains of C. botulinum will be investigated over a range of different physiological conditions. The model system will investigate the effects of different concentrations of acetic acid and salt in conbination with various temperatures and pH. It will be established at pH 5.5, 6, 7 and temperatures of 15, 20 and 30°C. Salt concentrations used will be 0, 5, 7.5%. Ten-percent salt will be used in some of the initial experiments. Some growth/no-growth boundary experiments will be required as well the use of 2.5% salt. Acetic acid concentrations of 0, 0.5 and 1% will also be used.

Part-baked breads containing acetate will be inoculated with a cocktail of proteolytic spores at a concentration of 10&#179 cfu/g. The bread will be incubated aerobically and under vacuum at 5°C and 20°C.

Minimally processed sous-vide type products will be challenged with a cocktail of non-proteolytic C. botulinum spores and these will also be incubated at 5&#176C to establish whether growth would occur.

Results and findings

The aim of this project was to extend the Clostridium botulinum Food MicroModel models and validate them in a range of additional food types (e.g. part-baked breads, vacuum-packed pasta products, sous-vide products, etc.). Food validation studies have been carried out and work has been conducted on the acetate model including growth/no growth boundaries.

For the acetate model the following growth/no-growth boundaries were established:

At 15&#176C growth occurred at pH 6 and 7 at 0% salt at all three acetate concentrations. For all the other conditions no growth was observed.
At 20&#176C growth was observed at pH 5.5, 6 and 7 at 0% salt and at 5% salt at pH 7. At 0% salt and at pH 7 growth was only observed at 0% acetate. At 5% salt and pH 7 growth occurred at 0 and 0.5% acetate. At pH 6 and 7 at 0% salt growth was evident at all three acetate concentrations.
At 30&#176C no growth was observed at a salt concentration of 7.5%. At 5% salt growth was measured at 0% acetate and a pH of 5.5. At pH 6 and 7 growth was further observed at 0.5% acetate. At 0% salt growth occurred at all three acetate concentrations for pH 5.5, 6 and 7.

Challenge tests with proteolytic spores in breads with acetate proved to not show any growth at any of the incubation conditions used. These products appeared to be safe. Similarly to the results from the bread challenge tests no growth was observed in any of the minimally processed products that were inoculated with a cocktail of non-proteolytic spores.

The purpose of this project was to address the limitations of recently developed models of growth of C. botulinum . The results from the project improved the acetate model with a wider range of conditions and concentrated in particular on growth and no-growth boundaries of proteolytic strains of C. botulinum which has not been done before in such depth.

Proteolytic and non-proteolytic strains of C. botulinum were inoculated into breads and minimally processed foods, respectively. The outcome of this investigation was that none of the products permitted growth of C. botulinum and reassuring from the food safety aspect.

Contact : Email : science@foodstandards.gsi.gov.uk

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B01021: Challenging and validating Clostridium botulinum models for Food MicroModel

Background

Research Approach

Results and findings

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