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. 10⁸ CFU/g) and fermented for 12 h at 80°F (26.7°C) and then at 100°F (37.8°C) until the pH reached either 5.2 or 4.7. The mix was then heated to 110, 115, or 120°F (43.3, 46.1, or 48.9°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°F (43.3°C) for 20 h, 115°F (46.1 °C) for 10 h, or 120°F (48.9°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.