Theoretical and Experimental Investigation of the Thermal Inactivation of Thermoanaerobacterium Thermosaccharolyticum and Geobacillus Stearothermophilus in Different Canned Food Matrices

In the canning industry, thermal preservation processes typically are designed based on Clostridium botulinum thermal destruction kinetics. However, some bacteria can still survive, necessitating implementation of stricter timetemperature regimen for sterilization process. The aim of this study was to compare processing effectiveness at F₀ (sterilization value) 8 ±1 min from the perspective of the vegetable-based product canning facility, while analyzing the inactivation, viability, and recovery of thermophilic bacteria. Four commercial products [tomato soup and rassolnik soup - acidified food (AF), and mushroom soup and pea porridge - low-acid food (LACF)] with different heat transfer characteristics (convection and conduction) were inoculated with 6.6 log₁₀ spores/ml Geobacillus stearothermophilus LMKK 244 (reported as DSM 6790 and ATCC 10149 in other collections) and 4.8₁₀ log spores/ml Thermoanaerobacterium thermosaccharolyticum DSM 571 spore suspensions. Food samples contaminated with bacterial spores were processed in a steam-air retort at 118 °C for 75 min. G. stearothermophilus and T. thermosaccharolyticum growth was not detected in AF samples (pH = 4.4 and 4.5), but was observed in LACF samples (pH = 5.1 and 5.8). Practical evaluation showed that T. thermosaccharolyticum did not survive thermal processing, which was verified using a presence/absence test after incubation at 55 °C. G. stearothermophilus did not survive thermal processing, but recovered in pea porridge (pH = 5.8) during incubation. Our observations showed that food pH is a crucial factor determining microorganism survival during heat treatment and may be used by the vegetable-based product canning facilities to improve the food sterilization conditions.