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Some additives make Listeria more sensitive to irradiation.

Currently, producers of ready-to-eat (RTE) products use thermal and nonthermal techniques to inactivate, if not completely kill, microorganisms. But those treatments don't always prevent subsequent growth of bacteria under refrigeration conditions. At least 90 million pounds of RTE meat products have been recalled since 1998 in the United States because they were contaminated with L. monocytogenes. USDA-ARS scientists believe that for ground meats and some RTE products, irradiation may be the only effective means of treatment, since it can be used after packaging.

Although RTE meats are cooked, they should be reheated in some cases because they can become contaminated between the cooking and packaging steps. The FDA is reviewing, but has not yet approved, the use of irradiation for RTE meats such as hot dogs, bologna, and deli turkey and ham.

Investigators also have completed studies on the roles of food additives in inhibiting growth of injured pathogens in products during long-term refrigerated storage. Certain additives make Listeria more sensitive to irradiation. For instance, a mixture of salts of acetic acid (vinegar) and lactic acid in bologna formulations decreased the radiation dose needed to inactivate 99.999% of L. monocytogenes inoculated onto the meat from 3.0 kiloGrays (kGy) to 2.5 kGy. The mixture also prevented growth of spoilage microorganisms for two months. Ionizing radiation, when combined with common food additives, has the potential to significantly reduce the incidence of listeriosis associated with consumption of RTE meats in the United States.

Irradiation promotes the production of several volatile sulfur compounds associated with unpleasant odors that can sometimes occur in irradiated or overcooked RTE turkey meat. Adding antioxidants to RTE formulations has a limited effect on preventing production of the compounds. But a combination of common additives and mild heating reduced levels of sulfur compounds in RTE turkey meat by more than 50%, compared to irradiation alone.

The radiation resistance of L. monocytogenes and other pathogens depends on the product's formulation and the genetic characteristics of the contaminating strain. ARS researchers have established the radiation doses needed to inactivate L. monocytogenes in a variety of RTE meat products, and they've determined the radiation resistance of L. monocytogenes strains associated with foodborne illness.

Further information. Chris Sommers, USDA-ARS Food Safety Intervention Technologies Research Unit, Eastern Regional Research Center <>, 600 East Mermaid Lane, Wyndmoor, PA 19038; phone: 215-836-3754; fax: 215-233-6445; email: <>.
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Publication:Microbial Update International
Date:Apr 1, 2005
Previous Article:L. monocytogenes contamination of ready-to-eat meat products, even after a lethality treatment, is of major concern to the meat processing industry.
Next Article:Antimicrobials control L. monocytogenes on commercial frankfurters during storage.

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