Thermal Processing Parameters to Ensure a 5-logReduction of Escherichia coli O157:H7, Salmonella enterica, and Listeria monocytogenes in Acidified Tomato-based Foods

Under 21 Code of Federal Regulations Part 114, manufacturers of acidified canned foods must apply a process that ensures destruction of pertinent vegetative bacterial pathogens and spoilage organisms. We used nonlinear (Weibull) modeling to calculate thermal processing parameters sufficient to inactivate Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella enterica in tomato purée at 54°C. Inoculum (1 ml of a 5-strain single pathogen cocktail) was heated in 99 ml tomato purée at pH 4.50 (unacidified) or in purée acidified to pH 3.80 or 4.20 by use of acetic or citric acid. D54°C ranged from 20.85 min for E. coli O157:H7 in purée at pH 4.5; as well as 0.63 min for S. enterica in purée acidified to pH 3.8 by addition of acetic acid. Acetic acid was significantly more effective than citric acid in ensuring pathogen inactivation (P < 0.05). E. coli O157:H7 was significantly more heat- and acid-resistant than S. enterica and L. monocytogenes in tomato purée at pH 4.5, as well as in purée acidified to pH 4.2 by addition of citric or acetic acid (P < 0.05). L. monocytogenes was the most heat- and acid-resistant in purée acidified to pH 3.8 by addition of acetic acid, but in purée acidified to pH 3.8 with citric acid, there was no difference in the rate of pathogen inactivation. Extrapolating 5-log pathogen reduction times to relevant processing temperatures, E. coli O157:H7 was the most heat resistant at < 65°C (149°F), while L. monocytogenes was most heat resistant at temperatures above 65°C. Using a calculated z-value of 13.3°F (7.4°C) and F-value of 0.51 min at 160°F (71.1°C), time/temperature combinations to achieve a minimum 5-log pathogen reduction in tomato purée, pH ≤ 4.5, ranged from 13.83 min at 141°F (60.6°C) to 0.02 min at 180°F (82.2°C). Results can be used to inform development of scheduled processes and to support FDA process filings for tomato-based acidified foods.