Increased thermotolerance of Clostridium perfringens spores following sublethal heat shock

Beef gravy samples inoculated with Clostridium perfringens spores were heat shocked at 75 °C for 20 min, and then thermotolerance at 100 °C was assessed using a submerged-coil heating apparatus. Survivors were enumerated on Shahidi Ferguson Perfringens agar. An association of the heat resistance with the origin of the C. perfringens could not be established due to significant variations in the heat resistance among strains. Interestingly, deviations from classical logarithmic linear declines in the log numbers with time were not observed in both control and heat shocked samples. D-values at 100 °C for C. perfringens spores ranged from 15.5 to 21.4 min. Heat shocked spores of 9 out of 10 strains had significantly higher (p<0.05) D-values at 100 °C than unstressed spores. Proteins with epitopic and size similarity to Escherichia coli GroEL and Bacillus subtilis small acid-soluble protein, SspC, were present in spores. However, heat shock treated spores did not appear to significantly increase expression of these proteins. Acquired thermotolerance is of substantial practical importance to food processors and should provide useful information for designing thermal treatments to eliminate C. perfringens spores in ready-to-eat foods