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 (approximately 1.4 x 10(8) spores per g), and the product was treated with combinations of pressure (0.1 to 700 MPa) and heat (95 to 121 degrees 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 degrees C; however, at 121 degrees C the contribution of pressure to spore lethality was less pronounced. The zP-value increased from 170 MPa at 95 degrees C to 332 MPa at 121 degrees C, suggesting that B. amyloliquefaciens spores became less sensitive to pressure changes at higher temperatures. Similarly, the zT-value increased from 8.2 degrees C at 0.1 MPa to 26.8 degrees 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.

Strong and Consistently Synergistic Inactivation of Spores of Spoilage-AssociatedBacillusandGeobacillusspp. by High Pressure and Heat Compared with Inactivation by Heat Alone

“…Contrary to the case for proteolytic C. botulinum, there are a number of published studies suggesting that the most heat-resistant spoilage bacterium of concern for LASSF, Geobacillus stearothermophilus, is not nearly as resistant to thermal processing under high pressure as its heat resistance would predict (2,14,17,21,24). In comparison, strains of the aerobic mesophilic species Bacillus amyloliquefaciens, which produces spores with intermediate heat resistance, have been shown to produce highly HPTresistant spores (1,17,18,23) that under some conditions appear to be stabilized by high pressure against thermal inactivation (16). B. amyloliquefaciens is closely related to Bacillus subtilis and Bacillus licheniformis, but to date, the spores of these related bacteria have been found to be relatively sensitive to HPT processing (17,18,26).…”

“…B. amyloliquefaciens is closely related to Bacillus subtilis and Bacillus licheniformis, but to date, the spores of these related bacteria have been found to be relatively sensitive to HPT processing (17,18,26). A number of B. amyloliquefaciens strains have been proposed as relevant target spoilage organisms for 18) and even as potential surrogates to assess the efficacy of HPT processes with respect to proteolytic C. botulinum (23).In assessing the resistance of spores to inactivation by HPT processing compared with that achieved under thermal-only conditions, the primary approach of others (1,14,21,23,24) has been to compare inactivation as a function of the hold time, mostly assuming log-linear inactivation kinetics. For HPT inactivation, this approach ignores lethality accrued during the preheating, pressure come-up (CUT), and depressurization phases.…”

“…B. amyloliquefaciens is closely related to Bacillus subtilis and Bacillus licheniformis, but to date, the spores of these related bacteria have been found to be relatively sensitive to HPT processing (17,18,26). A number of B. amyloliquefaciens strains have been proposed as relevant target spoilage organisms for HPT-processed LASSF (17,18) and even as potential surrogates to assess the efficacy of HPT processes with respect to proteolytic C. botulinum (23).…”

Participation in the Center for Advanced Processing and Packaging Studies

“…For PATP treatment, appropriate aliquots of spore suspension were aseptically added to 50 mM sterile HEPES buffer containing antimicrobial compounds at selected concentrations (or without antimicrobial compounds as controls) in sterile pouches to obtain ~ 4.7 x 10 8 CFU/ml. The heat-sealed pouches were stored at 4 o C for 1 h and treated in duplicate at 600 MPa and 105 o C for 2 min in a high pressure microbial kinetic tester (PT-1, Avure Technologies Inc., Kent, WA) as described by Rajan et al (2006). The 2-min treatment time at 600 MPa…”

“…The spores were prepared according to the method of Rajan et al (2006) using nutrient agar as the sporulation medium supplemented with 0.6% yeast extract and 10 ppm MnSO 4 .…”