Optimization and Evaluation of Heat-shock Condition for Spore Enumeration Being Used in Thermal-process Verification: Differential Responses of Spores and Vegetative Cells of Clostridium sporogenes to Heat Shock

다국어 초록 (Multilingual Abstract)

To evaluate a heat-shock condition for the enumeration of Clostridium sporogenes spores, a surrogate for C. botulinum spores, we examined the heat tolerance of C. sporogenes spores and vegetative cells exposed to a heat shock at 90^oC. From the D values of the spores determined in the temperature range of 113-121^oC, z value (±SD) and D90°C value were estimated to be 10.16±0.90^oC and 1,071.52 min, respectively, and the inactivation rates were predicted to be only approximately 2% at 90^oC for up to 10min. Meanwhile, the viable count of spores was significantly higher when activated under a heat-shock condition of 90^oC for over 9 min than those activated for shorter time periods. The heat tolerance of vegetative cells was extremely low, showing a D90°C value (±SD) of 0.21±0.01 min.
Finally, 3 different heat-shock conditions were compared:70^oC for 30 min, 80^oC for 20 min, and 90^oC for 10 min,and the experimental comparative data showed no significant differences in viable spore counts. Consequently, these results support that the heat-shock treatment at 90^oC for 10min is suitable to activate spores and to inactivate vegetative cells of C. sporogenes.

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