Reaching critical limits

by Kerri Gehring and Jeffrey Savell
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Although establishing Critical Limits – when putting together Hazard Analysis Critical Control Points (HACCP) programs – seems rather straightforward, based on our experiences in HACCP-training classes, assisting establishments with their HACCP plans and in writing and maintaining Texas A&M’s Rosenthal Meat Science and Technology Center’s HACCP plans, this simple HACCP principle can be quite difficult.

Let’s first review the definition of Critical Limits from the National Advisory Committee on Microbiological Criteria for Foods: “A maximum and/or minimum value to which a biological, chemical or physical parameter must be controlled at a CCP to prevent, eliminate or reduce to an acceptable level the occurrence of a food-safety hazard.”

It is clear that establishing Critical Limits was designed to put some sort of numerical or measurable value around the CCPs. If cooking is the CCP, then the temperature the product must reach and the time it must remain at that temperature become the Critical Limit. It seems simple, right? But, one now has to determine: what temperature is critical; how much time is needed at that temperature; is it surface temperature or internal temperature, etc. It is at this point where greater thought and additional information must be applied by the HACCP team to ensure that Critical Limits are scientifically supportable and defendable for regulatory purposes.

Critical Limits are typically derived from three areas:

1. Regulatory standards or guidelines - For establishments that prepare ready-to-eat products, USDA’s Appendix A for lethality and Appendix B for stabilization are the two most-commonly used guidelines for setting Critical Limits for cooking and chilling of products. Establishments that follow these must ensure they follow all components of them. Examples of this would be cooking in an oven with at least “90 percent relative humidity for at least 25 percent of the total cooking time but in no case for less than 1 hour” for Appendix A, and then making sure that the temperature declines within the allowed times are met for chilling products according to Appendix B.

2. Literature surveys and industry guidelines - The most-commonly used literature survey in HACCP plans is the document that Dr. Bruce Tomkin of Armour-Swift-Eckrich prepared on a number of temperature-related factors that influence pathogen growth. The Good Manufacturing Practices for Fermented Dry & Semi-Dry Sausage Products developed by the American Meat Institute is another often-used document. Literature surveys are an underutilized source of Critical Limits, and further work by food microbiologists, food chemists and other experts in various fields could really help provide documents that could be used by meat and poultry processors in establishing these limits.

3. Experimental results - We often assume that large establishments are more likely to generate their own information for very specific products that may not have known Critical Limits for the control measures for the hazards of concern because of the costs involved with conducting such research. Some uses of experimental results come from scientific journal articles where many of the pathogen interventions, such as application of organic acids to carcasses, cuts or trimmings, are the source of Critical Limits. The challenge with this source of establishing Critical Limits is that scientific papers often report multiple parameters associated with the application of these interventions (e.g., concentration, pressure, temperature, volume, pH). Determining what the true “critical parameters” are can be a great source of debate and can lead to regulatory consequences if the agency feels that the scientific support for the Critical Limits is not being fully implemented.

Setting parameters

As stated in the last section, the term, “critical parameters” has become a real challenge for meat and poultry processors who use scientific articles to support their Critical Limits, but who do not fully follow everything that the article reports when the specific intervention is used. As scientists, we know that for a scientific study to get published, as many details of the process as can be measured are required by the reviewers and editors of journals because the intent of this level of specificity is to ensure that the study could be repeated in another laboratory with similar results. From a practical standpoint, scientists also know that not all parameters measured and published are actually “critical parameters” and required for control.

The greatest area for debate is separating what is simply a “nice to know” from a “required measurement.” Most pathogen interventions, such as organic acids, are most effective based on their concentration, the temperature at which they are applied and whether they are sufficiently applied to ensure proper surface coverage. Parameters such as pressure of application, time period of application, etc., are often much less critical if the first three are met, but there are no true protocols to follow to differentiate between “critical” and “non-critical” parameters.

Operating limits are another area that presents problems with meat and poultry establishments. These are the limits where the process may be optimal, such as fully cooking for optimum flavor/tenderness development or freezing for maximum shelf-life characteristics. Too often, establishments want to make their operating limits their Critical Limits so that the employees will have one set of values to follow. The problem with this is that operating within the Critical Limits signifies whether the CCP is “in” or “out” of control, and if the Critical Limits are simply set the same as the operating limits, then if the process is out of those boundaries, the product may not be of the same quality, but there may not be an issue with safety.

Another issue is when establishments set a range of parameters as the Critical Limit. For example, organic acid interventions have a minimum concentration required to control the identified pathogens, which is the Critical Limit; however, some establishments will include a maximum level, which is often based on regulatory allowances for application, as part of the Critical Limit. However, the maximum level is an operational limit and is not associated with the ability of the organic acid to control the hazard, but with a potential labeling issue for failing to meet the application parameters defined by the agency. It is important that the Critical Limits are “the maximum and/or minimum value to which a biological, chemical, or physical parameter must be controlled at a CCP to prevent, eliminate, or reduce to an acceptable level the occurrence of a food-safety hazard.”

Finally, Critical Limits should only be used for CCPs and not for any other step in the process. The key is when Critical Limits are exceeded, the safety of the product may be in question and Corrective Actions should be taken.

Kerri Gehring is the president/CEO of the International HACCP Alliance and is an associate professor in the Dept. of Animal Science at Texas A&M Univ. Jeff Savell is Regents Professor and E.M. “Manny” Rosenthal Chairholder in the Dept. of Animal Science at Texas A&M Univ.

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