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United States Department of Agriculture

Agricultural Research Service

PMP FAQs - Choosing a Model
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1.  How do I determine the correct model to use for a cooling deviation?

a. Models are developed for specific environmental conditions. For example, the model may have been developed from data generated in a microbiological broth, in a specific food, or in synthetic food. In each case, the accuracy of model predictions is known only for the matrix for which it was developed. To learn more about the specific conditions under which a model was produced, read the associated references shown in the model window.

b. In certain instances, there may be multiple forms of a model, such as aerobic and anaerobic versions. In this case, choose the model that is closest to your product. For example, choose an anaerobic model if your product is vacuum packaged. Choose an aerobic model if you wish to understand how the bacteria will react when the package is opened and exposed to oxygen.

c. In many cases, you will not find a model that exactly matches your food product’s formulation. In this case, it is advisable to choose a model that will provide more liberal estimations of growth or inactivation. For example, culture media (broth) models typically predict shorter Generation Times (or higher growth rates) than those observed in food. This is true as long as you set the environmental parameters (temperature, pH, water activity/NaCl) to the values that match your food. A similar example is that a sterile raw food model will normally predict shorter Generation Times (or higher growth rates) than a non-sterile raw food or one that contains inhibitory additives.


Last Modified: 1/20/2006