Thermal resistance of Listeria monocytogenes in Inegol meatballs

Abstract

This study was performed to determine the thermal resistance of L. monocytogenes at different heat treatments in Inegol meatballs. Inegol meatballs were divided into three groups. In group 1, meatballs were inoculated with 8.0 x 10(2), 1.9 x 10(3), 6.0 x 10(3) and 2.4 x 10(4) cfu/g L. monocytogenes and then they were cooked at an internal temperature of 85 degrees C for 4 min. Group II meatballs were inoculated with 1.0 x 10(2), 2.0 x 10(2), 8.0 x 10(2), 5.6 x 10(5) and 2.0 x 10(6) cfu/g L. monocytogenes and cooked at an internal temperature of 80 degrees C for 4 min. In group 111, the meatballs were inoculated with 5.6 x 10(5) and 2.0 x 10(6) cfu/g L. monocytogenes and cooked at an internal temperature of 63 degrees C for 30 min. In groups I and II, L. monocytogenes was not determined by direct plating method after cooking process. However, heat injured bacteria were recovered by an enrichment procedure when they were cooked at an internal temperature of 80 degrees C for 4 min. In group III, L. monocytogenes numbers were reduced by about 3 log cfu/g at 63 degrees C for 30 min. As a result, it was considered that the cooking process at an internal temperature of 85 degrees C for 4 min of Inegol meatballs is sufficient for eliminating L. monocytogenes when it is at <= 10(4) cfu/g level, and the heat treatment at 80 degrees C for 4 min was not adequate to completely eliminate the pathogen when its number was higher than 10(2) cfu/g but it decreased the L. monocytogenes levels to undetectable numbers. However, it was concluded that the cooking process carried out at 63 degrees C for 30 min did not entirely eliminate the high contamination (>= 10(5) cfu/g) of L. monocytogenes, and the meatballs may constitute a risk for foodborne listeriosis, especially in susceptible human hosts.