Modified Spore Inoculation Method for Thermal-Process Verification of Pinto Beans and Green Beans Canned in Two Large Reusable Containers

Comparison of viability and heat resistance of Clostridium sporogenes stored at different temperatures

The objective of this study was to determine the influence of storage temperature on the viability and heat resistance of Clostridium sporogenes spores. Spore suspension containing both spores and vegetative cells was divided into 3 groups to be stored at different temperatures of -20 (freezing), 4 (refrigerating), and 25 degrees C (ambient temperature). Samples stored for different times within the 2 mo were tested for viability by comparison of colony counts on plates and for heat resistance by determining D values at 121 degrees C. No significant differences were found in the viability of vegetative cells during the storage period, regardless of storage temperatures tested, while the viability of the spores stored for more than 4 wk was significantly higher at 4 degrees C than at -20 degrees C. The heat resistance of spores stored at 4 degrees C for more than 4 wk was remarkably higher than that at 25 degrees C, but similar to that at -20 degrees C throughout the storage period. Consequently, it turned out that a refrigerating temperature of 4 degrees C is satisfactory for storage of C. sporogenes spores in maintaining viability and heat resistance. This study suggests that storage temperature influences the viability and heat resistance of C. sporogenes spores.

Morphological study of heat-sensitive and heat-resistant spores of Clostridium sporogenes, using transmission electron microscopy

To investigate the primary structural determinants affecting heat resistance of Clostridium sporogenes spores, electron micrographs of heat-sensitive (D121 degrees C = 0.56 min) and heat-resistant (D121 degrees C = 0.93 min) spores of C. sporogenes were taken with a transmission electron microscope. The mean thickness (+/- standard deviation [SD]) of coat layers and cortex regions of heat-sensitive spores were 82.9 +/- 14.5 and 86.0 +/- 22.7 nm, while those of heat-resistant spores were 106.9 +/- 45.7 and 111.7 +/- 32.1 nm, respectively. The thickness of coat (P = 0.031) and cortex (P = 0.006) showed statistically significant differences, suggesting that heat-resistant spores have a thicker coat and cortex than do heat-sensitive spores. The mean sizes (+/- SD) of cores were 467.0 +/- 88.7 nm for heat-sensitive spores and 460.2 +/- 98.5 nm for heat-resistant spores, respectively, which showed no statistically significant differences. The ratios (+/- SD) of the core size to the sporoplast size were 0.84 +/- 0.05 for heat-sensitive spores and 0.80 +/- 0.07 for heat-resistant spores, respectively, showing statistically significant differences (P = 0.030), which indicated that the ratio is negatively related to heat resistance. Accordingly, the structural components of heat-sensitive spores were severely damaged by heat treatment, whereas those of heat-resistant spores were unlysed under the same conditions. Based on the structural analyses of spores, it was elucidated that the thickness of coat layer and cortex region are significantly correlated with heat resistance of C. sporogenes spores, and that cortex region plays a major role in protecting the spore from heat damage.