Food Safety and Inspection
National Advisory Committee on
Posted March 7, 2002
National Advisory Committee on Microbiological Criteria for Foods Work Group Assignment: Supplemental Information
Potential Scientific Parameters that Must be Considered to Establish Global Dates for Refrigerated Ready-To-Eat Foods
The development and subsequent analysis of the draft FDA/FSIS microbial risk assessment on “The Relative Risk to Public Health from Fooborne Listeria monocytogenes Among Selected Categories of Ready-to-Eat (RTE) Foods," reinforced the relationship between the temperature and time of refrigerated storage and the microbiological safety of refrigerated ready-to-eat (RTE) foods. Foods that had relatively low levels of initial contamination at manufacturing but which supported the growth of L. monocytogenes, were in many instances found to pose a sufficient risk if the duration and temperature of storage permitted significant growth. Inversely, despite often having significant frequencies of contamination, foods that did not allow growth of the pathogen typically did not have elevated levels of the pathogen at the time of consumption and generally were not associated with an increased risk of disease. Further, the risk assessment predicted that refrigerators operating at high temperatures (> 50 F) led to a disproportionate fraction of illnesses. While information on the distribution of storage times associated with refrigerated RTE foods is limited, the analysis suggested that preventing storage for excessive times would also have a marked effect in reducing the number of illnesses.
While the temperature and duration of refrigerated storage on RTE foods is particularly important for psychrotrophic pathogens such as L. monocytogenes, these factors can also impact the risks associated with mesophilic pathogenic bacteria. Typically, gram-negative enteric pathogens such as Salmonella or enterohemorrhagic Escherichia coli do not grow below temperatures of 8 to 10 C. However, at marginal abuse temperatures in the range of 10 to 12 C, growth of E. coli O157:H7 and other enteric pathogens can be relatively rapid. It is generally assumed that the more extended the shelf-life of a refrigerated RTE food, the more likely it is that the product will be exposed to one or more periods of marginal temperature abuse prior to consumption.
It has been suggested that the various storage time recommendations that currently appear on food labels seem to be based on quality attributes. The goal of the current request to the National Advisory Committee on Microbiological Criteria for Foods (NACMCF) is to have the Committee consider the scientific parameters and data that would be needed to develop “safety-based” “use-by” date labels for RTE foods. This document is intended to provide some of the related issues that may need to be considered in responding to the charge that has been presented to the Committee. The issues presented are for illustrative purposes only and should not be considered all inclusive.
Selection of Target Organisms and “Safety-Based” End Points
Two parameters that are prerequisites for the development of “safety-based” “use-by” date labels are the microorganism of concern and the biological end point that will serve as the basis for the shelf-life value. To date, it has generally been assumed that the target organism for RTE foods should be L. monocytogenes. However, it could be argued that it would be beneficial to use a surrogate microorganism that has a higher rate of growth at refrigeration temperatures. Once the target microorganism is selected, the end point that should be the basis for decision-making must be agreed upon in order to set the “use-by” date. Typically, the end point that has been considered has been that of the food having been subjected to conditions that lead to some degree of growth (e.g., < 1 log cycle). Ideally, the end point selected is one that correlates with an agreed upon increase in the risk of adverse health effects.
In developing shelf-life criteria based on quality attributes, it is generally assumed that a portion of the consumers will use the product after the recommend shelf life. This is taken into account in setting the shelf-life dates. One referenced value seen is that consumers will generally consume or discard a product within a period that is 1.3 times the stated shelf life.
Some of the related issues that have arisen about the selection of the target organism and shelf-life end point are:
Modeling the Growth of Pathogenic Bacteria
Considering the wide range of products, product formulations, and production facilities, as well as the wide diversity of practices associated with the distribution, marketing, and consumption of RTE foods, it does not seem feasible to conduct inoculated pack studies on more that a limited number of product classes. Accordingly, it is assumed that the modeling of microbial growth will play an important role in the development of “safety-based” “use-by” date labels. During the past decade there has been extensive research directed toward the development of mathematical models that describe the growth characteristics of L. monocytogenes and other foodborne pathogenic bacteria.
Modeling techniques are being used extensively in the development of both the FDA/FSIS and FAO/WHO L. monocytogenes risk assessments. In applying growth models, several assumptions were made by the FDA/FSIS and FAO/WHO risk assessment teams in order to achieve realistic representations of the “real world.” Several of these assumptions are outlined below as examples of potential parameters that may have to be considered in the development of “use-by” dates.
Very few inoculated pack studies have been conducted to determine when spoilage and rejection of the food by the consumer would occur. The current modeling approaches may project storage periods and growth beyond a reasonable time. However, L. monocytogenes does not produce as obvious an organoleptic change in the food as do many other microorganisms. The chocolate milk outbreak where many people consumed 109 cfu/ml illustrates this phenomenon.
Some of the related issues that have arisen in regard to possible modeling approaches are:
Differentiating Foods that Do or Do Not Support Growth
As indicated above, a key parameter that influences the risk of RTE foods being associated with human cases of listeriosis is their ability to support the rowth of L. monocytogenes.
Some of the related issues that may need to be considered are:
The biological systems that make up the disease triangle (pathogen, host, and food) for foodborne diseases are noted for their diversity. Traditionally, food safety experts have dealt with this diversity by seeking the “worst case scenario.” However, this typically leads to highly conservative food control systems. With the advent of microbial risk assessment techniques, it is increasingly possible to directly consider diversity in the analysis of food safety data and the subsequent development of microbiologically-based criteria such as “safety-based” “use-by” date labels.
Related issues that may need to be considered are:
Validation and Verification
It is assumed that validation and verification will be integral parts of the establishment and use of “safety-based” “use-by” date labels.
Some of the related issues that may need to be considered are:
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