Pressure Combined with Heat Reduces Prion Infectivity in Processed Meats

WASHINGTON -- The combination of high temperature and very high pressure in the preparation of processed meats such as hot dogs and salami may effectively reduce the presence of infective prions while retaining the taste, texture, and look of these meats, according to a study in today's Proceedings of the National Academy of Sciences (PNAS) Early Edition.

The study was led by Paul Brown, MD, of the National Institute of Neurological Disorders and Stroke (NINDS), a component of the National Institutes of Health within the U.S. Department of Health and Human Services. Other collaborators on the study, which was conducted in Europe with partial funding provided by the Ministero della Salute, Italy, included Rich Meyer (Tacoma Farms, Washington) and Franco Cardone and Maurizio Pocchiari (both with the Ministero della Salute).

Scientists believe that bovine spongiform encephalopathy, also known as "mad cow" disease, entered the human food chain through beef products containing abnormal, or folded, proteins called prions. The disease manifests itself in humans as variant Creutzfeldt-Jakob disease. Since 1995 more than 140 patients, mostly in the United Kingdom, have died as a probable result of eating contaminated meat products.

Scientists have been looking for strategies to inactivate any possible infectivity in meats, and although processes such as autoclaving and exposure to strong alkali or bleach are known to kill prions, they cannot be used successfully in food preparation.

Richard T. Johnson, MD, former neurologist-in-chief at the Johns Hopkins University School of Medicine and a senior advisor to the National Institutes of Health on the transmissible spongiform encephalopathies, said "the idea of using high pressure to decrease prion activity is interesting and unique and may lead to additional studies." Extensive surveillance by the U.S. Department of Agriculture has not detected bovine spongiform encephalopathy in the United States. The transmission of prion diseases through the food chain is a concern among public health officials.

To conduct the study, the scientists prepared a paste of scrapie prion-infected brain tissue mixed with hot dogs. They then exposed the paste to temperatures of 120-135 degrees Celsius (250-275 degrees Fahrenheit) and short bursts of ultra high pressure, in excess of 100,000 pounds per square inch. The scientists found that they were able to retain the basic texture and flavor of the processed meat while reducing the prions to non-infective levels. This may have application in improving the safety of meat products.

The combination of temperature and high pressure has been used commercially for the past 15 years to reduce the amount of bacteria in foodstuffs and to preserve ham, chicken, salsa, and other foods. Brown said his team "took the process one step further, to see if it would kill prions, which it did." He called the discovery a relatively inexpensive, practical step to potentially improve the safety of processed meats.

He added the approach may have implications for understanding the prion structure. "At a constant high temperature, we know that more and more prion inactivation occurs at higher and higher pressures. We hope that studying the structure of prions at increasing levels of pressure may allow us to better understand how the abnormal prion misshapes or unfolds," said Brown.

The NINDS is a component of the National Institutes of Health in Bethesda, Maryland, part of the U.S. Department of Health and Human Services, and is the nation's primary supporter of biomedical research on the brain and nervous system.

Source: National Institutes of Health