Control L. monocytogenes on deli meat.

Listeria species are widely distributed in the environment and are found in soil, on plants, decaying vegetation, silage and water. L. monocytogenes is the major species that causes disease in both humans and animals. It has been isolated from raw and processed foods, including dairy products, meats, vegetables and seafood.

It's assumed that large numbers of L. monocytogenes cells must be ingested to cause an illness. However, foods contaminated with low numbers of cells are a concern because the pathogen can grow in many products that are stored under refrigerated conditions. An outbreak of listeriosis in 1998 and 1999 was associated with the consumption of frankfurters and possibly deli meats. This outbreak brought about an increased interest in controlling the bacteria on frankfurters and deli meats.

Applying approved chemicals with antimicrobial properties to the surfaces of processed meat may provide a safeguard to contamination by L. monocytogenes. The objective of scientists at the Center for Food Safety (University of Georgia, Griffin Campus, Griffin, GA 30223) was to identify GRAS chemical preservatives that can inactivate L. monocytogenes or control its growth on chicken luncheon meat.

Slices of luncheon meat were treated by evenly spraying onto their surfaces a solution of one of four preservatives--sodium benzoate, sodium propionate, potassium sorbate and sodium diacetate--at one of three concentrations (15%, 20% or 25%). The residual concentration of preservative on meat slices treated with the 25% solution was approximately 0.15%, based on the entire l5-g slice.

In all instances, the degree of growth inhibition was directly proportional to the concentration of preservative. Only sodium diacetate was highly inhibitory to L. monocytogenes on meat slices held at 22 C for seven days or longer. Untreated luncheon meat held at 22 C was visibly spoiled within 10 days. There was no evidence of visible spoilage on any treated luncheon meat at 14 days of storage. The overall keeping quality of luncheon meat as judged by appearance was markedly improved by the four surface treatments.

Results indicate that 25% solutions of selected GRAS chemicals sprayed onto the surfaces of chicken luncheon meat slices greatly reduced the potential for substantial growth of L. monocytogenes within 14 days at 4 C and 13 C. At 22 C, sodium diacetate inactivated the pathogen during product storage.

The three concentrations of sodium benzoate or sodium diacetate decreased the initial population of L. monocytogenes by 0.78 to 1.32 log10 cfu/g at day 0. Reductions by the sodium propionate or potassium sorbate treatments were only 0.14 to 0.36 log10 cfu/g. During storage at 4 C, L. monocytogenes populations continued to decline on all treated meat slices, but they increased on untreated slices. At day 14, the populations on meat treated with sodium diacetate or sodium benzoate and held at 4 C were 2 to 3 log10 cfu/g less than on the untreated slices. They were 1.5 to 2 log10 cfu/g less than on slices treated with sodium propionate or potassium sorbate.

After storage at 13 C for 14 days, populations of the bacteria were 3.5 and 5.2 log10 cfu/g less on meat slices treated with 25% sodium benzoate or 25% sodium diacetate, respectively, and about 2 log10 cfu/g less when treated with 25% sodium propionate or 25% potassium sorbate than on the untreated slices.

Further information. Michael Doyle; phone: [phone]; fax: [phone]; email: [e-mail].