Destruction of Escherichia coli O157:H7 and Salmonella typhimurium in Lebanon bologna by interaction of fermentation pH, heating temperature, and time

Fermented meats have caused food-borne illness due to enterohemorrhagic Escherichia coli. Consumption of Lebanon bologna was epidemiologically associated with a recent outbreak of salmonellosis. The present study was conducted to determine the effects of pH (after the fermentation step), final heating temperature, and time on destruction of E. coli O157:H7 and Salmonella typhimurium in Lebanon bologna. Raw Lebanon bologna mix was inoculated with either of the pathogens (ca. 10(8) CFU/g) and fermented for 12 h at 80 degrees F (26.7 degrees C) and then at 100 degrees F (37.8 degrees C) until the pH reached either 5.2 or 4.7. The mix was then heated to 110, 115, or 120 degrees (43.3, 46.1, or 48.9 degrees C). The bologna was sampled at various times, decimally diluted, and plated on either McConkey sorbitol agar or XLD agar to enumerate E. coli O157:H7 and S. typhimurium, respectively. Fermentation alone reduced populations of both pathogens by 2 log units and heating alone reduced populations of E. coli O157:H7 by 3 log units. A combination of fermenting to either pH 5.2 or 4.7, followed by heating at 110 degrees F (43.3 degrees C) for 20h, 115 degrees F (46.1 degrees C) for 10 h, or 120 degrees F (48.9 degrees C) for 3 h reduced populations of both pathogens by 7 log units. Overall, S. typhimurium cells were either equally or significantly less resistant (P 0.01) than cells of E. coli O157:H7. Significant interactions (P 0.01) among the three factors for the destruction of E. coli O157:H7 were observed. A process-specific regression equation was developed to predict the destruction of E. coli O157:H7 in Lebanon bologna