Inactivation of Bacillus spores in batch vs continuous heating systems at sterilisation temperatures

Abstract

This study was performed to assess the heat resistance of spores of Bacillus species in batch and continuous heating systems under commercial sterilisation conditions. Spores of thermophilic Bacillus smithii and mesophilic Bacillus amyloliquefaciens were found to be highly heat resistant in the batch system. They were able to withstand typical sterilisation temperatures. B. amyloliquefaciens showed tailing in the batch system and, before the onset of the tailing, a higher inactivation rate than in the continuous system at low temperatures. The reason for the tailing might be the presence of spore aggregates which are disrupted in the continuous system.

Bacterial spores isolated from ingredients, intermediate and final products obtained from dairies: thermal resistance in milk

“…Stoeckel et al (2014a) showed that the inactivation of the spores from B. amyloliquefaciens F85 was non-log-linear whereas the inactivation of the spores from Bacillus smithii F64 was loglinear, which corroborates the results presented in this study. In the study of Stoeckel et al (2014a), tailing of the spores of B. amyloliquefaciens F85 at 120 and 125°C was already observed after holding times <250 s. At 110°C, the inactivation was markedly slower. At this temperature, the tailing phase was not reached yet or was about to start after a heat treatment of 30 min.…”

“…The spores apparently possess a highly heat-resistant fraction that is not inactivated even after holding times of 30 min at 120 and 125°C as shown in this study. Varying spore counts during the tailing phase of Mean log reduction 5.1 b ± 2.2 6.0 ± 1.0 6.2 ± 1.0 2.9 b ± 1.7 5.7 ± 1.0 6.0 ± 0.8 a Data from Lücking et al (2013) b Values are significantly different B. amyloliquefaciens F85 were observed by Stoeckel et al (2014a), which might explain the increased spore counts after treatments at higher temperatures as observed in this study for a few isolates. This study highlights that spores showing non-log-linear inactivation are able to persist at low spore counts over a wide range of temperatures and holding times (see e.g.…”

“…The temperature development in the tubes was monitored continuously and directly in the medium. Approximately 15 s was needed for heating up and for cooling down the medium (Stoeckel et al 2014a). The holding time started when the desired temperature ± 0.5°C was reached in the heating medium.…”

Establishment of markerless gene deletion tools in thermophilic Bacillus smithii and construction of multiple mutant strains

“…Sporulation deficiency is desired in industrial settings both for practical and safety reasons. B. smithii was shown to have highly thermo-resistant spores [ 23 , 24 ] and was found to be the most dominant species together with Geobacillus pallidus (recently renamed to Aeribacillus pallidus [ 16 ]) as highly thermostable spores in food. Both species were found to be non-cytotoxic [ 23 ].…”

Thermal Inactivation of the Heat-Resistant Pathogens Salmonella Senftenberg 775W and Escherichia coli AW1.7 in Whey Concentrate

“…Comparison of heat inactivation data between different studies is difficult because they mostly differ in the matrix, heating equipment, and test strains used. In particular, the enhanced shear stress in continuous heating systems results in increased inactivation compared to batch heating systems mimicking a similar temperature-time profile [26]. In the case of Salmonella, however, a study by D'Aoust [27], who worked with S. senftenberg strain 775W and 20 other serovars and who used equipment similar to the pilot plant pasteurizer used in this study, is somewhat suitable for comparison.…”