Scientists at Purdue University have developed a post-packaging pasteurization process for ready-to-eat meats that eliminates contamination by deadly bacterial food contaminants.

Scientists at Purdue University, West Lafayette, Ind., have developed a post-packaging pasteurization process for ready-to-eat meats that eliminates contamination by deadly bacterial food contaminants.

The scientists used sliced bologna tainted with Listeria monocytogenes, packaged it in vacuum-sealed plastic bags, and then submerged the packages in hot water, says lead researcher Tim Haley of Purdue's Center for Food Safety Engineering. Next, they immediately placed the bagged luncheon meat in cold water. This two-step procedure killed the microbes and also apparently extended the meat's shelf life.

The pasteurization method is called a high-temperature-short-time process. Although bologna and Listeria were used for this study, the process could be applied to similar deli meats and could eliminate other pathogens. Haley presented his findings at the Institute of Food Technologists' annual national meeting June 15-19 in Anaheim, Calif.

"The problem with ready-to-eat meats, including luncheon meat, hot dogs and deli meat, is that prior to final packaging, Listeria still can contaminate it," says Haley, an assistant professor in the Department of Food Science and director of the Computer Integrated Food Manufacturing Center. "This can happen if the bacteria are present in the air, on the equipment or in the water in the processing plant. If the food handlers have been exposed to Listeria, they can spread it even if they are wearing gloves."

Researchers have focused on Listeria because as few as 10 of the bacteria cells can cause illness and, though it is a relatively rare biological contaminant, its fatality rate of 20 percent is the highest of the food pathogens, according to the Centers for Disease Control and Prevention.

The research enabled the scientists to calculate the temperature and time needed to kill as many as 1 million of the organisms on one slice of bologna, Haley says. According to this model, the pasteurization process requires 185oF (85oC) water for 20 sec in such a scenario. If two slices are pasteurized, the length of hot water immersion is increased to 60 sec, and for four slices, 180 sec. This is followed by a 39oF (4oC) water bath for the same amount of time as in the hot water.

However, the scientists report that it is not practical to do more than two slices in a package using the method because the amount of time needed to pasteurize more than two slices would cause too much quality degradation.

But with just two slices in a package, the process didn't harm the quality of the bologna, Haley says. His research team will study ways to modify the process to accommodate meats with higher fat content.

In addition, having one or two slices wrapped together can a convenience to consumers, in much the same way as individually wrapped cheese slices, Haley says.

Other researchers involved in the study are Osvaldo Campanella, associate professor in the Department of Agricultural and Biological Engineering; Arun Bhunia, associate professor in the Department of Food Science; and David Gerrard, professor in the Department of Animal Sciences.

USDA Agricultural Research Service provided funding for this study. For more information, visit Purdue's Center for Food Safety Engineering web site at www.cfse.purdue.edu.