DMRI Predict contains a range of valid models for predicting the growth of selected pathogens in meat and meat products. DMRI Predict is an essential tool in the quality manager’s toolbox, and the latest addition is the Yersinia model:”Growth or reduction of Yersinia enterocolitica during curing of meat”.
Yersinia is salt tolerant and psychrotrophic
Yersinia enterocolitica can be found in healthy pigs and can potentially spread to the fresh meat during the slaughter and cutting process. Y. enterocolitica can grow at temperatures as low as 1°C and in salt concentrations of up to 5-7%. There is therefore a risk that Y. enterocolitica can grow during the curing process in the production of cured meat. Existing predictive models, such as Combase Predictor, lack the necessary parameters to ensure that the predictions for Y. enterocolitica can be related to cured pork.
Predictive model for risk assessment
Based on the risk of growth in cured meat, DMRI initiated a three-year project in 2017 aimed at generating data for documenting how the growth of Y. enterocolitica can be minimised during the production of cured meat and during storage of cured finished products. Based on the data generated in a large number of growth trials, the objective was to develop a mathematical model in which the calculations for the growth of Yersinia can be adapted to specific products with respect to temperature, pH and salt content. The aim is therefore to create a model that can serve as a tool the quality manager can rely on when conducting risk assessments.
In order to develop a model, it is necessary to generate large quantities of data that cover the range of factors included in the model. The model’s factors were selected in collaboration with Danish processing companies:
- Salt concentration of added brine (0.9-6.1% salt added to the meat)
- pH of the meat (5.5-6.4)
- Storage time (1-7 days)
- Storage temperature (2-12°C)
- Amount of nitrite added (0-200 ppm)
All of the trials were conducted in a small-scale set-up in the laboratory, where the meat was inoculated, cured and tumbled and subsequently stored at different temperatures. The meat was inoculated with a cocktail of six Yersinia strains with varying properties, including response to salt, nitrite and pH. It was decided to use a cocktail of strains to ensure a broad range of applicability of the model. During the storage trial, samples were regularly taken for microbiological and chemical analyses, so that the relationship between growth/no growth and a given factor (e.g. salt concentration) could be closely monitored.
Validation in the pilot plant
With respect to the model’s robustness and applicability in an industrial setting, the model was validated in a pilot scale set-up using industrial equipment. The validation was performed using pork loin and belly in order to simulate the curing process in the production of smoked pork fillet and bacon, respectively. Combinations of the factors used in the validation trials were selected with a view to ensuring prediction in the limits for growth/no growth.
The Yersinia model
You need to have the values for salt and nitrite in the meat after swelling, the pH of the fresh meat and the temperature during the curing process ready for entry. For the temperature during curing, it is possible to use a dynamic storage temperature or a constant storage temperature. Since the water activity, which is important for bacterial growth, is not always known, the fat or water percentage of the meat is entered, and then the water activity value will be calculated in the model.
As the model’s output, a graph is created that shows the model’s prediction of growth of Y. enterocolitica under the specified conditions over a period of seven days. Furthermore, the model’s prediction of the maximum growth rates of Y. enterocolitica is shown as a function of one of the following parameters: salt, nitrite, pH and temperature. This function makes it possible either to assess how close you are to the limit for growth/no growth under the specified conditions or to assess how much the selected parameter value needs to be changed in order to avoid growth.
The Yersinia model is robust
The model has been validated in a pilot scale set-up using data from the curing and tumbling of pork loin and belly. Data generated during the validation trials were used to verify and adapt the final model to ensure that the predictions are valid and robust. Since the model is intended for industrial use, it was decided that it should give a slight overprediction in the limits between growth and no growth, and the model is therefore considered to be fail-safe.
Get free access to the model here www.dmripredict.dk