THE EFFICACY OF A BOILING WATER BLANCH ON THE INACTIVATION OF LISTERIA MONOCYTOGENES IN DICED CELERY

Abstract

The effect of a boiling water blanch on the thermal inactivation of Listeria monocytogenes in raw diced celery was investigated. L. monocytogenes, Scott A was heated in Tryptic Soy Broth with 0.6% yeast extract, pH 5.3, at 52, 54, 56, 58, and 59°C. D values were 13.33, 7.75, 1.29, 0.792, and 0.701 min, respectively. A predicted D value at 60°C = 0.36 min was obtained using a z value of 5. These thermal inactivation characteristics were subsequently used to evaluate the L. monocytogenes was recovered from inoculated (1 X 10^7 cells/g) diced raw celery after heating for 0.25 min in a laboratory boiling water blanch. Viable cells were not recovered after 0.5 min of heating. Heat penetration data for diced raw celery during a boiling water blanch were obtained in a commercial setting. These data were analyzed by the general method to determine the cumulative lethality at reference temperatures of 60°C using a z of 5 and, 70 and 71.7°C using a z of 10. It was determined that a recommended process of 2 min at 70 °C was reached in 80 sec during the blanch. Based on the findings of this study, a boiling water blanch could be used as part of the hurdles approach to eliminate L. monocytogenes from raw diced celery.