Survival of Listeria monocytogenes in Postpasteurized Precooked Beef Roasts

The potential for Listeria monocytogenes to survive various times and temperatures of postpasteurization in precooked beef roasts was investigated. Precooked eye of round roasts were inoculated with 10⁹ cells of L. monocytogenes per package prior to packaging in cook-in bags and postpasteurization. Four groups of roasts (n = 54) each containing 27 uninoculated and 27 inoculated roasts were allotted to four pasteurization treatments consisting of two different exposure temperatures (91°C, 96°C) and two different dwell times (3 min, 5 min). Equal numbers of inoculated and uninoculated roasts from each treatment were then stored at 4 and 10°C. Triplicate samples of inoculated and uninoculated roasts were sampled on day 1, 4, 8, and 12 for product stored at 10°C and 1, 8, 14, 28, and 56 d for product stored at 4°C. Survivors were encountered for every treatment employed. The lethality of the treatment was directly related to an increase in dwell time and postpasteurization temperature. Treatment 4 (96°C, 5 min) was found to decrease the L. monocytogenes population the greatest (p < 0.05) and also maintained a lower (p < 0.05) count from its initial inoculum level during storage at both 4 and 10°C.