Development of a predictive model for the growth of Listeria monocytogenes in pasteurized blue crab ( Callinectus sapidus ) meat

Listeria monocytogenes (Lm) is a Gram-positive intracellular pathogen that is found in a variety of seafood and seafood processing plants. We previously reported prevalence and sources of Lm in Maryland blue crab meat and blue crab processing plants. However, a predictive models for risk management of Lm in blue crab meat has not been reported. Objectives: The objective of this study was to develop a predictive model for the growth of Lm in pasteurized blue crab meat as a function of storage temperature, and to compare model predictions to Lm growth in unpasteurized fresh crab meat. Methods: Three Lm strains isolated from fresh blue crab meat were inoculated into pasteurized crab meat and incubated at 0, 2, 5, 10, 15, 20, 25, 30, 35, 40, 45 and 45°C for selected time intervals. For each time interval, Lm viability was measured by direct-plating samples onto Modified Oxford agar, in duplicate. The model predictions were compared to Lm viability kinetics in unpasteurized fresh crab meat at 5, 15 and 30°C using the same protocol as for pasteurized crab meat, in two trials. The Baranyi D-model was fitted to Lm viability data to estimate parameters of lag phase duration (LPD), growth rate (GR) and maximum population density (MPD). The secondary model was produced using the Ratkowsky square root model. Results: Lm replicated at 0, 2, 5, 10, 15, 20, 25, 30, 35, 40, and 45°C with average GRs of 0.002, 0.11, 0.027, 0.059, 0.119, 0.222, 0.310, 0.423, 0.505, 0.524 and 0.214 log cfu/h, respectively. The highest GR, LPD and MPD were observed at 40°C (0.524 log cfu/h ), 0°C (187 h) and 30°C (10.1 cfu/g), respectively. The R2 value of the secondary model was 0.989, displaying acceptable bias and accuracy factors in fresh crab of 1.02 and 1.17, respectively. Conclusions: A predictive model was successfully produced for the growth rate of Lm in pasteurized crab meat from 0 to 45°C. It showed acceptable performance when applied to unpasteurized fresh crab over a range of 5 to 30°C. The model will assist the seafood industry and regulatory agencies in designing and implementing food safety plans to minimize the risk associated with this pathogen in crab meat.