Thermal Destruction of Listeria monocytogenes in Ground Pork Prepared with and without Soy Hulls.

D-values and z-values were determined for Listeria monocytogenes Scott A cells heated in raw ground pork prepared with and without soy hulls and in a soy hull/water mixture. Products inoculated with ca. 107 colony-forming units (CFU) per g were sealed in glass vials, immersed in a water bath, and held at 50, 55, 60, or 62°C for predetermined times. Survival was determined by testing heated samples with McBride listeria agar. The D-values for L. monocytogenes cells at 50, 55, and 60°C were 108.81, 9.80, and 1.14 min, respectively, when heating was in ground pork and 113.64, 10.19, and 1.70 min, respectively, when heating in ground pork with added soy hulls. At 62°C L. monocytogenes cells were inactivated too rapidly to permit determination of the D-value. The D-values for L. monocytogenes in the soy hull/water mixture at 50 and 55°C were 19.84 and 3.94 min, respectively. L. monocytogenes cells were inactivated too quickly to determine the D-value at 60°C. The z-values for L. monocytogenes in ground pork prepared with and without soy hulls were 5.45 and 5.05°C, respectively. If ground pork naturally contains 102 L. monocytogenes cells per g and if we want to assure safety with a 4-D Listeria cook (reducing the L. monocytogenes population by four orders of magniatude), then according to results of this study, ground pork must be heated to an internal temperature of 60°C for at least 4.6 min and ground pork with added soy hulls for at least 6.8 min.

Cook/Chill Foodservice System with a Microwave Oven: Coliforms and Aerobic Counts from Turkey Rolls and Slices 1.

Turkey was sampled for total aerobic plate counts and coliform counts, before and after cooking, after chilled storage and after reheating in a microwave oven. Frozen turkey rolls were thawed for 48 h at 3°C. Rolls were then cooked (105, 135 and 165°C) to an internal temperature of 77°C. Cooked rolls were placed into a refrigerator operating at 1°C and chilled for 24 h. Rolls were removed from the refrigerator, sliced and refrigerated for ≤ 2 1/2 h to simulate holding conditions in a hospital cook/chill foodservice system. Slices were reheated for 30 or 40 s in a microwave oven. For the raw product, total aerobic plate counts and coliform counts ranged from 78,000 - 615,000/g and 1,600 - 38,000/g, respectively. No coliforms were found in turkey rolls following cooking and chilled storage and turkey slices reheated in a microwave oven. Cooking turkey rolls resulted in reduction of two to five orders of magnitude in total aerobic plate counts. For most trials of the experiment, counts were further reduced when turkey slices were reheated in a microwave oven. These low microbial counts may be attributed to cooking turkey rolls to an end point temperature of 77°C and storing chilled at 1°C before reheating the slices in a microwave oven.