Thermal Resistance of Spores from Five Type E Clostridium botulinum Strains in Eastern Oyster Homogenates

The thermal resistance of spores from five type E Clostridium botulinum strains, Alaska, Minnesota, G21-5, 25V-1 and 25V-2, in oyster homogenates was determined at 73.9, 76.7, 79.4, and 82.2°C. Thermal death times (TDT) were determined in TDT tubes containing 1-g sample and heated using a constant temperature water bath for different time intervals. D values ranged from 0.07 to 0.43 min at 82.2°C (180°F) and from 2.00 to 8.96 min at 73.9°C (165°F). One strain (Minnesota) isolated from a botulism outbreak in Minnesota was the most heat resistant while strains isolated from crabs (G21-5, 25V-1, and 25V-2) were least resistant. The z values were 4.2 to 5.4°C for strain (Alaska) associated with an outbreak and 6.0 to 7.1°C for the other four strains. Results indicate that these organisms are less heat resistant in oyster homogenate than other seafood products. However, current oyster pasteurization methods are not sufficient to guarantee safety from type E. C. botulinum spores, and further studies are needed to assure product safety.