Solvent extraction as an adjunct to rendering: the effect on BSE and scrapie agents of hot solvents followed by dry heat and steam

The study was designed to determine the effect on bovine spongiform encephalopathy (BSE) and scrapie agents of the solvent extraction processes used in the past by British renderers. The raw material was mouse spleen infected with either the 22A strain of scrapie agent or the 301V strain of BSE agent. Samples were exposed to hexane, heptane, petroleum spirit or perchlorethylene at the relevant temperatures for the appropriate times. Control samples were exposed to the same range of temperatures for the same range of times in saline. Other samples were exposed to the hot solvents, followed by treatment with dry heat at 100 degrees C for 30 minutes and steam at 100 degrees C for 30 minutes. Further samples were exposed only to the dry heat and steam cycles. No single complete process was significantly more effective than any of the others, and they all produced only slight inactivation, less than one log on average for both strains of agent. The average degree of inactivation produced by exposure to hot saline was generally comparable to that produced by exposure to the hot solvents. This was also true for the samples exposed only to dry heat and steam compared with those exposed to hot solvent before treatment with dry heat and steam, and suggests that the slight inactivation was caused by the heat rather than by the solvents. It is concluded that the solvent extraction processes used by renderers in Britain had little capacity to inactivate BSE and scrapie agents.