Inactivate pathogens using low doses of ionizing radiation.

Outbreaks of foodborne illness and product recalls are occasionally associated with ready-to-eat (RTE) sandwiches and other heat-and-eat multi-component RTE products. Ionizing radiation can inactivate foodborne pathogens on raw meat and poultry, fruits and vegetables, seafood and RTE meat products.

Unfortunately, not much data are available on the ability of low-dose ionizing radiation--doses of less than 5 kGy typically used for pasteurization purposes--to inactivate pathogenic bacteria on complex multi-component food products. With this in mind, USDA-ARS scientists investigated the ability of low levels of ionizing radiation to inactivate Salmonella spp., L. monocytogenes, S. aureus, E. coli O157:H7 and Y. enterocolitica on RTE foods, including a frankfurter on a roll, a beef cheeseburger on a bun and a vegetarian cheeseburger on a bun. Their research indicates that this approach may be an effective way to inactivate common foodborne pathogens in complex RTE food products such as heat-and-eat sandwiches.

Individual bacterial species--three isolate mixtures--were inoculated onto the surface of each product and irradiated in a self-contained irradiator at 0.095 kilogray (kGy) per min, at 4 C in an aerobic environment. The scientists enumerated the surviving bacteria using standard microbiological techniques in order to determine the D-10 value. The D-10 value is the radiation dose needed to inactivate one log10 of a target microorganism in kGy.

The average D-10 value was 0.61, 0.54, 0.47, 0.36 and 0.15 kGy for Salmonella spp., S. aureus, L. monocytogenes, E. coli O157:H7 and Y. enterocolitica, respectively. A low radiation dose of 1.25 kGy was able to inactivate less than 2 log10 of Salmonella spp., the most radiation-resistant of the pathogens tested, on each of the three products tested. A radiation dose of 2.5 kGy was able to inactivate less than 4 log10 of Salmonella spp. Further information. Christopher Sommers, Food Safety Intervention Technologies Research Unit, USDA-ARS Eastern Regional Research Center, 600 E. Mermaid Lane, Wyndmoor, PA 19038; phone: [phone]; fax: [phone]; email: [e-mail].