PMP FAQs - Types of Models

 

General Issues:

1. Are there models for Campylobacter bacteria?
   
   Currently, the PMP does not contain models for this species.
   
   
2. Are there spoilage models?
   
   Currently, the PMP only contains models about the effects of irradiation on spoilage bacteria.
   
   

Survival (Non-Thermal Inactivation) Models:

1. What acidulant (acid) was used in the broth models to adjust pH?
   
   You should read the publication for the model to determine the acid that was used. In general, survival (Non-Thermal Inactivation) models were developed using an organic acid (lactic acid) as the acidulant.
   
   

Heat Inactivation Models:

1. Can I use the PMP inactivation models to measure process lethality?
   
   In their current form, PMP models are not suitable for determining process lethality calculation. To make these calculations, it is necessary to know the Z value and Tref temperature, and to be able to calculate F values over a range of changing temperature. We are currently developing a new tool to perform these calculations in future versions of the PMP inactivation models. If you know the valid Z value and Tref for your food product, then you can use these with a spreadsheet tool that can be downloaded from the American Meat Institute's website.
   
   

Cooling Models:

1. Why won't my complete time-temperature profile show in the cooling input table?
   
   You can only enter up to 50 combinations of time and temperature in the cooling profile box.
   
   
2. How do I input cooling profile data into the Cooling model?
   
   You can directly type in your cooling profile data in the table on the left of the screen or you can import the data from a file. To learn how to input the data, click on the "Show me how" button at the bottom of the time-temperature window. After following these directions, you can import the time-temperature data by clicking on the "Import Cooling Profile" button at the bottom of the time-temperature window.
   
   
3. Can you use these models if you do not know the product temperature but you know the room temperature where the product is maintained?
   
   No. You must measure the temperature of the product, specifically the part of the product that has the highest temperature.
   
   
4. What does it mean when my cooling profile is similar to the times in the USDA Food Safety & Inspection Service Appendix B, yet the PMP C. perfringens or C. botulinum model shows more than 1.0 log₁₀ of growth?
   
   The minimum recommended cooling times listed in Appendix B are a guide for safely cooling meat products. Depending on the food product, these times may result in a prediction of more than 1 log₁₀ of growth. As stated in Appendix B "If the product remains between 120^oF and 80^oF more than one hour, compliance with the performance standard is less certain." However, you would need to validate the model in your food product before knowing that the model makes accurate predictions.
   
   

Clostridium botulinum Models:

1. How do I interpret the C. botulinum models?
   
   The USDA Food Safety & Inspection Service (9CFR-Docket 95-033F) states that the cooling profile of a product cannot result in growth of C. botulinum. In some instances, the PMP C. botulinum cooling model may predict a value of growth that is less than 0.3 log₁₀. A predicted value lower than 0.3 log₁₀ does not represent growth, because the log₁₀ for one multiplication of C. botulinum is 0.3 log₁₀ or greater.