High-Pressure Inactivation of Transmissible Spongiform Encephalopathy Agents (Prions) in Processed Meats

The epidemic of bovine spongiform encephalopathy (BSE) that began in the late 1980s and has so far been responsible for over 200 human fatalities caused by the ingestion of contaminated beef products stimulated research into disinfection methods appropriate for both animal feed and human food. As it turned out, the risk of infection was almost entirely eliminated by government and industry bans, first on the use of recycled bovine tissues in cattle feed (the source of the epidemic in bovines) and, second, the exclusion of potentially contaminated bovine tissues from beef products consumed by humans. A third approach, had the first two not been successful, was a disinfection method compatible with the aesthetic and nutritional quality of beef products. In this chapter, we review the results of a series of experiments that were undertaken to explore optimal conditions for the commercial use of a combined high-temperature and high-pressure inactivation of BSE prions in processed meats. In repeated experiments, we were unable to detect any significant effect on infectivity from a two-hour exposure to 60 degrees C at pressures between 400 and 800 MPa. In a further large series of experiments conducted with a variety of machines at different facilities, we found that a 5-min exposure to temperatures and pressures in the range of 120-130 degrees C and 600-700 MPa yielded, on average, a 100-fold (2 log) reduction in infectivity. Depending on assumptions about the potential infectious load in a given beef product, this level of disinfection, although useful, cannot be guaranteed to eliminate the risk of disease transmission to humans.