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May 23, 2002

USA: Simple post-packaging process halts deadly food contaminant

Scientists from Purdue University have discovered a simple post-packaging pasteurisation process for ready-to-eat (RTE) meats that eliminates contamination by the deadliest of the bacterial food contaminants. Lead researcher Tim Haley, from Purdue's Centre for Food Safety Engineering, explained that the scientists used sliced bologna tainted with Listeria monocytogenes, packaged it in vacuum-sealed plastic bags, and then submerged the packages in hot water. Next, they immediately placed the bagged luncheon meat in cold water.

Scientists from Purdue University have discovered a simple post-packaging pasteurisation process for ready-to-eat (RTE) meats that eliminates contamination by the deadliest of the bacterial food contaminants.

Lead researcher Tim Haley, from Purdue’s Centre for Food Safety Engineering, explained that the scientists used sliced bologna tainted with Listeria monocytogenes, packaged it in vacuum-sealed plastic bags, and then submerged the packages in hot water. Next, they immediately placed the bagged luncheon meat in cold water.

This two-step procedure, called a “high-temperature-short-time process”, killed the microbes and also apparently extended the meat’s shelf life.

Haley, who will present his findings at the Institute of Food Technologists’ annual national meeting in Anaheim, California on 15-19 June, said that while bologna and Listeria were used for this study, the process could be applied to similar deli meats and could eliminate other pathogens. Haley said the method possibly could be part of a national biosecurity system to protect against deliberate attempts to cause illness through food contamination.

“The problem with RTE meats, including luncheon meat, hot dogs and deli meat, is that prior to final packaging, Listeria still can contaminate,” said 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 ten of the bacteria cells can cause illness and, though it is a relatively rare biological contaminant, its fatality rate of 20% is the highest of the food pathogens, according to the Centers for Disease Control and Prevention (CDCP).

Haley and his team investigated pasteurisation as a possible way to eliminate food pathogens from RTE meats because similar processes have been used for other foods, and it is something food manufacturers could easily and quickly implement.

Haley said that according to his model, the pasteurisation process requires 85°C (185°F) water for 20 seconds for one slice of meat. If two slices were pasteurised, the length of hot water immersion would be increased to 60 seconds, and for four slices, 180 seconds. This would be followed by a 4°C (39°F) water bath for the same amount of time as in the hot water.

However, the scientists report that it’s not practical to do more than two slices in a package using the method. This is 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 said. The researchers used both low-fat and regular bologna that can be purchased in retail food stores. 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 would be a convenience to consumers, in much the same way as individually wrapped cheese slices, Haley said.

“This approach is similar to the pasteurisation method used for canned food and milk, so it should be acceptable to consumers as a safeguard against bacterial contamination,” he said.

The USDA’s Agricultural Research Service (ARS) provided funding for this study.

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