Thermal Inactivation of Listeria monocytogenes in Whole Oysters (Crassostrea belcheri) and Pasteurization Effects on Meat Quality

This study assesses the practical thermal inactivation of Listeria monocytogenes in whole oysters (Crassostrea belcheri) and the quality changes in meat caused by pasteurization (57.5-70.0 degrees C). The D-value decreased from approximately 4 minutes to half a minute when the temperature was increased from 57.5 to 70.0 degrees C. The z-value of L. monocytogenes was approximately 12.6 degrees C. In the study of physical, chemical, microbiological, and sensory quality effects on pasteurized oyster meat, the 6D conditions for L. monocytogenes were used in processing at 57.5-70.0 degrees C temperatures. It was found that the cooking loss and the b* color coordinate of oyster meat increased, whereas cutting strength, L*, a*, and moisture content decreased (P < 0.05) with treatment temperature. The pH of oyster meat was not significantly affected by the choice of treatment, and no total viable count (TVC) was found in any sample. In the sensory evaluation, odor, texture, and overall acceptability were not significantly affected by the treatment temperature. Only some specific descriptors related to oyster appearance and taste had significant differences between treatments in the sensory evaluation scores. Results from this study are useful for timing the thermal treatment of vacuum-packed whole oysters to inactivate L. monocytogenes.