Help Understanding HARPC's Appendix 3 Tables (Bacterial Pathogen Growth and Inactivation)

Hi everyone,

I am looking for resources to understand time/temperature processing and how it relates to pathogen growth and inactivation. I understand it depends on the medium (e.g., water activity), but wanted to get a general sense. 

FDA has their HARPC Draft Guidance  which includes Appendix 3: Bacterial Pathogen Growth and Inactivation. The only thing is... I'm not sure if my understanding of the tables is correct! 

Table 3A - the guidance states it "contains information on the minimum water activity (aw), minimum and maximum pH, and minimum and maximum temperatures that limit growth for the bacterial pathogens that are of greatest concern in food processing". Am I correct to understand that these are the conditions that the pathogens listed can grow at? For example, Bacillus cereus cannot grow when water activity < 0.92, outside the pH of 4.3 - 9.3, or outside the temperatures of 39.2 - 131F? 

Table 3B - Time and Temperature Guidance for Controlling Pathogen Growth and Toxin Formation in Food Products - the guidance states it "contains information on maximum cumulative exposure time at internal product temperature ranges for exposure of foods that, under ordinary circumstances, will be safe for the bacterial pathogens that are of greatest concern in food processing. These maximum, cumulative exposure times are derived from published scientific information". This table confuses me because the highest product temperature listed is above 70F. But I would expect the exposure time would differ if it's 90F vs. 170F? But they don't account for that. 

Some context - I'm trying to look for literature concerning dehydration of fruits that would constitute a kill step. The process I'm looking at dehydrates at 80C for several hours. I know a validation study should be carried out to, but I'm curious if there's already literature that shows general time/temperature inactivation dynamics of pathogens. So if you have any to share, please do! 

3A - you are correct. 

3B - This is a general guidance for food exposed to temperatures outside of proper storage. The table is showing limited information, though. If you compare it to a replication curve of mesophiles you would see that replication rate grows exponentially until its peak around normal body temperature and falls quickly near its kill zone. So you are correct that holding times would differ, but sometimes it's better to have a quick and dirty guideline.

If you then look at table 3D you can get a sense of how long bacteria need to be held above its max temperature to be considered an effective kill step. Hotter + longer is more effective, but you must consider your finished product.

Consult table 1H for your common pathogens then go to 3B for your ranges. Send finished product to the lab to verify/validate.