Thermal Inactivation of Stationary-Phase and Acid-Adapted Escherichia coli O157:H7, Salmonella, and Listeria monocytogenes in Fruit Juices

Abstract

The heat resistance of stationary-phase and acid-adapted Escherichia coli O157:H7, Salmonella enterica (serotypes Typhimurium, Enteritidis, Gaminara, Rubislaw, and Hartford), and Listeria monocytogenes was evaluated in single-strength apple, orange, and white grape juices adjusted to pH 3.9. The heat resistance increased significantly (P < 0.05) after acid adaptation. Salmonella had an overall lower heat resistance than the other pathogens. Acid-adapted E. coli O157:H7 presented the highest heat resistance in all juices at the temperatures tested, with lower z-values than Salmonella and L. monocytogenes. The heat resistance (D60°C-values) of all three pathogens, assessed in tryptic soy broth adjusted to different pH values, increased above pH 4.0. From the results obtained in this study, one example of a treatment that will inactivate 5 logs of vegetative pathogens was calculated as 3 s at 71.1°C (z-value of 5.3°C). Normal processing conditions calculated for hot-filled, shelf-stable juices achieve a lethality in excess of 50,000 D for all three pathogens.