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APPLICATION OF VALIDATION/SUPPORT MATERIALS:

CONTROL OF MESOPHILIC PATHOGENS THROUGH USE OF WATER ACTIVITY

Prepared by: The American Meat Institute Scientific Validation Subcommittee A subcommittee of the American Meat Institute Scientific Affairs Advisory Committee

4/25/2005 1 DRAFT DRAFT THIS INFORMATION IS MADE AVAILABLE BY THE AMERICAN MEAT INSTITUTE AS A PUBLIC SERVICE, WITHOUT EXPRESS OR IMPLIED WARRANTIES OF ANY KIND, AND SUBJECT TO THE FOLLOWING DISCLAIMERS: 1. ACCURACY AND CONTINUITY OF SERVICE. The American Meat Institute (AMI) makes no guarantee of the completeness or accuracy of any information provided. AMI makes no promise or warranty to maintain or update this service or information contained and made available to the public. The user assumes the risk of verifying any materials used or relied on. 2. NO WARRANTIES. AMI disclaims any express or implied warranty in providing for use any materials, information, graphics, products, or processes contained therein. AMI makes no warranty, express or implied, nor assumes any responsibility in the use of this material or its contents for its accuracy, completeness, currency, its use for any general of particular purpose, nor that such items or use of such items would not violate or infringe rights of others. 3. COPYRIGHT LIMITATIONS. The State has made the content of these pages available and anyone may view, copy or distribute information found here without obligation to AMI, unless otherwise stated on particular materials or information to which a restriction on free use may apply. However, AMI makes no warranty that materials contained herein are free of Copyright claims or other restrictions or limitations on free use or display. 4. ASSUMPTION OF RISK OF USE. A user of this information assumes the risk of use or reliance on such information. Neither AMI, its employees nor agents shall be liable for any damages for using these materials.

4/25/2005 2 DRAFT DRAFT APPLICATION OF VALIDATION/SUPPORT MATERIALS:

CONTROL OF MESOPHILIC PATHOGENS THROUGH USE OF WATER ACTIVITY

POTENTIAL CCP: LOW, INHIBITORY WATER ACTIVITY

EXAMPLES OF HAZARDS CONTROLLED BY THE POTENTIAL CCP:

The controlled water activity will prevent the growth of mesophilic pathogenic , including monocytogenes, E. coli O157:H7, and Campylobacter.

EXAMPLES OF WHERE THE POTENTIAL CCP MIGHT BE USED:

Low water activity control may be used as a CCP for applications including the following:

§ Shelf stable ready-to-eat (RTE) meat and poultry products, e.g., country cured ham, pepperoni, salami and jerky § Refrigerated RTE meat and poultry products formulated to have an inhibitory water activity, e.g., fermented sausages, country cured hams

SUPPORT DOCUMENTATION/PUBLISHED LITERATURE:

Background on water activity

Water activity refers to unbound water in a product; and thus, is not the same thing as moisture content. may have the same moisture content, but different water activity values. The water activity scale extends from 0 (bone dry) to 1.0 (pure water); but most foods have a water activity level in the range of 0.2 to 0.99. In more technical terms, water activity measures the generated by the moisture present in a hygroscopic product, and is defined by the following equation:

water activity = p/ps

Where p is the partial pressure of water vapor at the surface of the product and ps is the saturation pressure, or the partial pressure of water vapor above pure water at the product temperature. Thus, water activity reflects the part of the product moisture that can be exchanged between the product and its environment under normal conditions.

The water activity of most hygroscopic products is not highly dependent upon temperature and varies little over the range of temperatures that support microbial growth. At room temperature, water activity varies by about 0.0005 to 0.005 Water activity when the temperature changes by 1 °C.

The impact of water activity on microbial growth and survival

Water activity is most useful in predicting the growth of bacteria, yeasts and molds. Food can be made safe by lowering the water activity to a point that will not allow dangerous bacteria to 4/25/2005 3 DRAFT DRAFT grow. Table 1 lists the minimum water activity values that allow the growth of pathogens. In general, growth of most bacteria is inhibited by water activity values near 0.92; the actual inhibitory level is dependent not only on the bacterial species, but also on the solutes present that reduce the water activity, e.g., glycerol vs. .

Microorganism must compete with solute molecules for free water molecules, and with the exception of , most bacteria are poor competitors. Minimum water activity values for bacteria represent those values where growth is minimal; below these values, the bacteria, or a proportion of the population die. Survivors may remain their infectious nature.

Water activity does influence the ability of heat to kill bacteria, e.g., Salmonella Typhimurium is reduced tenfold in 0.18 minutes and 4.3 minutes at 60 °C when the water activity is 0.995 and 0.94, respectively.

The impact of water activity on growth and survival is dependent upon other food characteristics such as pH, temperature and acidity.

Affect of water activity on

Research has been done to assess the impact of water activity on L. monocytogenes. Debevere (1989) was one of the first to suggest that the suppression of growth in products containing lactate was a result of a reduction in the water activity. Lactate (2%) lowered the water activity of liver pate from 0.959 to 0.945. Ryser and Marth (1991) reported that L. monocytogenes could grow in laboratory media adjusted to water activity values near 0.93 and survive at lower water activity values. Johnson et al. (1988) reported that L. monocytogenes survived at least 84 days at 4 °C in fermented hard salami with a water activity of 0.79 to 0.86 with levels as high as 7.8%, nitrite at 156 ppm and pH near 4.3.

Chen and Shelef (1992) reported that the addition of lactate to strained beef reduced water activity. The highest moisture content at which the listeristatic effects of 4% lactate were produced was 55%, corresponding to a water activity of 0.964. In lactate-free samples, listeristatic effects occurred at 25% moisture and a water activity of 0.932. Although 2% NaCl and 4% sodium lactate both reduced the water activity to 0.962, the effect of NaCl on growth of Listeria was negligible, again pointing out the impact of the solute on the efficacy of the reduced water activity on reducing growth.

Regulatory implications for water activity

It is generally accepted that the lowest water activity value at which a foodborne pathogen, S. aureus, will grow is 0.86. Consequently, the Food and Drug Administration and the and Inspection Service (FSIS) consider foods with a water activity value of 0.85 or below not to be potentially hazardous.

FSIS (2003) states that:

Since products with water activity less than 0.85 will not support the growth of L. monocytogenes and can sometimes even cause L. monocytogenes death, FSIS will consider water activity of < 0.85 at the time the product is packed to be a post-lethality treatment if there is a listericidal effect in the specific product and the establishment has provided support documentation to document the intended effect occurs prior to 4/25/2005 4 DRAFT DRAFT distribution of the product into commerce. In this case, the antimicrobial process could serve as both a post-lethality treatment and growth inhibitor. The establishment should have documentation on file to demonstrate the effectiveness of the lethality treatment through the of the product. These shelf stable products can be classified in Alternative 1, …

The 2003 Listeria Rule defines Alternative 1 products as products as those that have received a post lethality treatment and an antimicrobial agent or process, and Alternative 2 products as those that have one or the other, but not both (USDA, FSIS, 1999). Low water activity has been shown to kill L. monocytogenes and prevent growth, thus meeting both requirements (Doyle et al., 1997; ICMSF, 1996). Thus, for products such as cooked bacon that has received an initial lethality treatment that results in a finished product with a water activity of 0.85 or less, the product would be classified as Alternative 1.

It is worth noting that despite the reference to a water activity value of 0.85 throughout the FSIS Compliance Guidelines, the Compliance Guidelines also contain a table based on an ICMSF publication (1996) that references a minimum water activity of 0.92 for growth of L. monocytogenes. This could factor into classification of a product as Alternative 2 despite a water activity above 0.85.

References

Chen, N. and L.A. Shelef. 1992. Relationship between water activity, of lactic acid, and growth of Listeria monocytogenes in a meat model system. Journal of Food Protection. 55:574- 578.

Debevere, J.M. 1989. The effects of sodium lactate on the shelf life of vacuum-packed coarse liver pate. Fleischwirtsch. 69:223-224.

Doyle, M.P., L.R. Beuchat, and T.J. Montville (eds.) 1997. Food Microbiology Fundamentals and Fronteirs.

FSIS. 1999. Appendix A: Compliance Guidelines for Meeting Lethality Performance Standards for Certain Meat and Poultry Products.

ICMSF. 1996. Microorganisms in Foods 5. Microbiological Characteristics of Food Pathogens. Blackie Academic & Professional, NY.

Johnson, J.L., M.P. Doyle, R.G. Cassens, and J.L. Schoeni. 1988. Fate of Listeria monocytogenes in tissues of experimentally-infected cattle and in hard salami. Applied & Environmental Microbiology 54:497-501.

Ryser, E.T. and E.H. Marth. 1991. Listeria, listeriosis and food safety. Marcel Dekker, Inc. NY.

Seeliger, H.P.R. and D. Jones. 1987. Listeria, pp. 1235-1245. In Bergey’s Manual of Systemic Bacteriology, 9th edition. Williams and Wilkens, Baltimore.

4/25/2005 5 DRAFT DRAFT Table 1. Minimum Water Activity Supporting Growth of Bacteria in Foods

Water activity Bacteria inhibited 0.95 E. coli C. perfringens Bacillus spp. 0.92 L. monocytogenes 0.91 C. botulinum Salmonella spp. 0.86 S. aureus

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