New research quantifies Clostridium botulinum spores in raw food materials

15th January 2016

QuichePCA study from the Institute of Food Research has provided new evidence on the background levels of spores of Clostridium botulinum in raw food ingredients that is helping the food industry deliver safe chilled foods more sustainably.

Botulism is a serious form of food poisoning, caused by a deadly neurotoxin produced by the bacterium Clostridium botulinum. The neurotoxin is so poisonous that eating even the tiniest amount of food in which C. botulinum has germinated, grown and formed neurotoxin can result in severe illness and death. Because of this, the food industry uses high quality raw materials and good hygienic manufacturing practice along with a strict set of safety criteria when producing foods. The safety criteria include precisely defined cooking conditions and times, as well as controlled storage temperatures and use by dates that keep our food safe. The rare outbreaks of foodborne botulism have occurred when these criteria haven’t been followed correctly.

Although these criteria are well established, consumer demand for reduced preservatives, milder heat processing and longer shelf lives is driving continuous innovation in minimally processed chilled foods, which include ready meals and similar prepared items. But delivering this needs a full understanding of how these changes affect the germination and growth of food poisoning bacteria, especially C. botulinum.

Professor Mike Peck and Dr Gary Barker from IFR’s Gut Health and Food Safety Programme have played a key part in a very successful research project called SUSSLE (Sustainable Shelf Life Extension (SUSSLE). IFR collaborated with the Chilled Food Association and Unilever Research to enhance the sustainability of minimally processed chilled foods by using quantitative risk assessment to set a safe shelf life with respect to C. botulinum, and reduce energy usage for minimally processed chilled foods. The SUSSLE project was co-funded by the food industry, Defra and the Biotechnology and Biological Sciences Research Council.

Clostridium botulinum - Andy Carter

Clostridium botulinum – Andy Carter

To quantify the risks it was necessary to generate vital new information concerning how many C. botulinum spores there are in raw food materials before they are processed. Spores of C. botulinum are present in lots of different environments, but only become dangerous when they germinate, and produce their deadly toxin in our foods. Minimising the risk of this happening starts with an assessment of the initial spore load in food. An optimized protocol developed by Prof. Peck and his team is considered a very sensitive enumeration method for spores in food materials, able to detect as few as 10-100 spores per kilogram. However, the actual level of contamination with spores is usually lower than this, and just one spore could be enough to germinate and cause botulism.

To overcome the problem of measuring spore loads that are close to the limit of detection, the researchers combined information from hundreds of historical studies with dedicated experimental and statistical approaches to quantify typical spore loads for different food types.

“The evidence shows that for many raw food materials, typical spore loads are smaller than previously reported” said Professor Peck. “This makes a big difference to how we make decisions about food safety and risk assessment.”

These findings can be used to improve active surveillance of foods, by showing how resources could be best used in this area. For meat, fish, shellfish and fungi, additional control experiments involving expected spore loads are most valuable, but for other foods testing additional samples is more effective. In particular, additional tests for spores in herbs and spices would be most beneficial.

Through the SUSSLE project products are now on supermarket shelves that have been produced with lower energy inputs, with safe extended shelf lives, and improved consumer acceptability.

Many members of the Chilled Food Association have benefitted from the project to date, through attending workshops hosted by IFR.  After 1st January 2018 manufacturers who aren’t members of the CFA will also be able to access the SUSSLE technology on special terms.

For more information please contact the Food Safety Centre

Reference: Quantification of non-proteolytic Clostridium botulinum spore loads in food materials, Barker G. C., Malakar P. K., Plowman J., Peck M. W. Applied and Environmental Microbiology  doi: 10.1128/AEM.03630-15

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