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

Abstract

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 102L. 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.