Thermal resistance parameters for pathogens in white grape juice concentrate

Abstract

The heat resistance of Escherichia coli O157:H7, Salmonella, and Listeria monocytogenes that were in stationary phase, had been exposed to high osmotic pressure, or were acid adapted was evaluated in white grape juice concentrate (58°Brix, pH 3.3). The most heat-resistant cells of all three pathogens were those exposed to high osmotic pressure or in stationary phase. Unlike in single-strength juices, in concentrate the acid-adapted cells for all three pathogens were less heat resistant than were cells in the other physiological states. E. coli O157:H7 had the highest heat resistance for all temperatures tested (e.g., D62°C = 1.8 ± 0.3 min, with a z-value of 9.9 ± 0.6°C). L. monocytogenes exposed to high osmotic pressure had the highest z-value (12.3 ± 1.2°C), although its D-values for all temperatures tested were lower (e.g., D62°C = 0.93 ± 0.1 min) than those for E. coli O157:H7. Salmonella was the most sensitive of the pathogens under all conditions. Based on the results obtained in this study, one example of a heat treatment that will inactivate 5 log units of all three pathogens in white grape juice concentrate was calculated as 1.5 min at 71.°C (z = 10.3°C). Validation studies confirmed the predicted D 71°C for E. coli O157:H7 exposed to high osmotic pressure. Copyright © International Association for Food Protection.