B13005: Expansion of the Perfringens Predictor model to include pH, nitrite and salt concentrations in its predictions

Study Duration: October 2005 to July 2006

Contractor: Institute of Food Research

Project B14009 has developed a user-friendly software tool (called Perfringens Predictor) that predicts the growth of Clostridium perfringens during the heating/cooling of meat. The Perfringens Predictor model enables the user to input temperature profiles into an Microsoft Excel spreadsheet and then provides a prediction of the growth of Clostridium perfringens under the specified dynamic cooling conditions. It also provides interpretation advice about the safety of the specified cooling profile.

The software and user manuals are available and can be downloaded from the Institute of Food Research website (see below).

The current version of the Perfringens Predictor model allows the user to input temperature during cooling, but does not allow the user to vary the pH, nitrite and salt concentrations. Current predictions are given under optimal conditions (pH 6.0 – 7.0, high water activity and no nitrite). However, the food industry have indicated that the pH of meats could be as low as 5.7 and the salt concentrations as high as 3.1% with a concurrent reduction in water activity. Moreover, nitrite up to a maximum concentration of 150ppm can be added.

This project aims to expand the Perfringens Predictor model to enable users to take account of such pH, nitrite and salt concentrations of the meat when making predictions. Expanding the Perfringens Predictor will make the model a more useful tool, providing more accurate and realistic predictions when pH, nitrite and salt concentrations are not optimal.

This project will use growth curves conducted at a single temperature to develop a dynamic model for growth that includes cooling temperature, pH, salt and nitrite. Existing growth data from ComBase will be supplemented with 30 new growth curves. The model will then be validated by comparison with literature data and new data generated in this project. New data will be generated under 20 different sets of pH/salt/nitrite and heating/cooling conditions. The user-friendly software will be revised to enable the user to input pH/salt/nitrite concentration. The major findings and user-friendly software will be widely disseminated.

A new, more dynamic version of the Perfringens Predictor model has been developed to predict the growth of Clostridium perfringens during the cooling of bulked meats that have been treated at 70-95&degC. The model is based on 84 growth curves including 22 new ones generated at the Institute of Food Research. It predicts growth within a range of 15-52&degC and predictions can be made for cured and uncured meat products.

This updated model has also been converted into a user-friendly software tool that enables the user to input pH (5.0-8.0), sodium chloride (salt) concentration (0.5%-4.0%) and sodium nitrite concentration (0-150 ppm). (Cured meats are classified as those with an initial sodium nitrite concentration of 100ppm or higher and a residual sodium nitrite concentration of 10ppm.)

The prediction of growth of Clostridium perfringens, based on the cooling profiles of pH, sodium chloride, and sodium nitrite concentration of the meat, was compared with observations of growth from 20 new heating/cooling curves carried out with different meats (pork, beef and turkey) at various pH, sodium chloride and sodium nitrite concentrations. Comparisons were also made to similar observations in literature. Analysing this collective data demonstrated that this latest version of the Perfringens Predictor Model provides a valid prediction of the growth of Clostridium perfringens during the cooling of meats as affected by the aforementioned parameters.

In addition to providing the user with a prediction of the growth of Clostridium perfringens, the software tool also provides the user with advice based on the interpretation of the results. It informs the user that, based on risk assessments carried out internationally, the Food Standards Agency recommends that the cooling of the meat should be sufficiently rapid to ensure that growth from heat-resistant spores of Clostridium perfringens is minimal, that is, it does not allow more than one log increase.

Perfringens Predictor Web Edition, an improved web-based version of the software tool and user manual, was launched in January 2007 and is available at the ComBase website (see external links at the bottom of this page). The advantage of this web-based version is that it more accessible than the previous Excel-download version. Several presentations have been made to highlight the availability, increased functionality and accessibility of the Perfringens Predictor.

The enhancement and expansion of the Perfringens Predictor model contributes to the Agency�s aim to reduce foodborne illness further, in this instance by reducing foodborne illnesses associated with Clostridium perfringens.

The final report is available from the Agency's Information Centre. To obtain a copy, please contact the Enquiry Desk, Information Services, Food Standards Agency (tel: 020 7276 8181/8182 or email: infocentre@foodstandards.gsi.gov.uk)

Contact: For any enquiries concerning this research project, please contact the relevant programme contact or email: science@foodstandards.gsi.gov.uk