Inactivation kinetics of selected aerobic and anaerobic bacterial spores by pressure-assisted thermal processing

Abstract

The combined pressure–thermal inactivation kinetics of spores from three strains of anaerobic ( Clostridium sporogenes, C. tyrobutylicum, and Thermoanaerobacterium thermosaccharolyticum), and six strains of aerobic ( Bacillus amyloliquefaciens and B. sphaericus) bacteria were studied. Spores of these bacteria were prepared in deionized water and treated in a custom-made kinetic tester over various pressure (0.1 and 700 MPa) and thermal (105 and 121 °C) combinations. Survivor data were modeled using log-linear and Weibull models to obtain relevant kinetic parameters. In comparison to thermal treatment alone, the combined pressure–thermal conditions accelerated the inactivation of the spores tested. A measurable fraction of spore populations was inactivated during the pressure come-up time. Pressure-assisted thermal processing (PATP) at 700 MPa and 121 °C for 1 min inactivated up to 7–8 log for some of spores tested. Among bacteria evaluated, based on survivor curve data T. thermosaccharolyticum, B. amyloliquefaciens Fad 82, and Fad 11/2 were found to produce the most PATP-resistant spores. PATP inactivation plots showed characteristic upward curvature, which is indicative of the tailing behavior. Since both log-linear and Weibull kinetic models did not consider microbial reduction during process come-up time, our results demonstrated that the estimated model parameters were not adequate to compare combined pressure–thermal resistance of various bacterial spores tested.