Combined Pressure-Thermal Inactivation Kinetics of Bacillus amyloliquefaciens Spores in Egg Patty Mince†

Abstract

Bacillus amyloliquefaciens is a potential surrogate for Clostridium botulinum in validation studies involving bacterial spore inactivation by pressure-assisted thermal processing. Spores of B. amyloliquefaciens Fad 82 were inoculated into egg patty mince (∼1.4 × 108 spores per g), and the product was treated with combinations of pressure (0.1 to 700 MPa) and heat (95 to 121°C) in a custom-made high-pressure kinetic tester. The values for the inactivation kinetic parameter (D), temperature coefficient (zT), and pressure coefficient (zP) were determined with a linear model. Inactivation parameters from the nonlinear Weibull model also were estimated. An increase in process pressure decreased the D-value at 95, 105, and 110°C; however, at 121°C the contribution of pressure to spore lethality was less pronounced. The zP-value increased from 170 MPa at 95°C to 332 MPa at 121°C, suggesting that B. amyloliquefaciens spores became less sensitive to pressure changes at higher temperatures. Similarly, the zT-value increased from 8.2°C at 0.1 MPa to 26.8°C at 700 MPa, indicating that at elevated pressures, the spores were less sensitive to changes in temperature. The nonlinear Weibull model parameter b increased with increasing pressure or temperature and was inversely related to the D-value. Pressure-assisted thermal processing is a potential alternative to thermal processing for producing shelf-stable egg products.