Apparatus for the simultaneous processing of mesophilic spores by heat-only and by high pressure and heat in a high pressure vessel to investigate synergistic spore inactivation

• Specialized pressure-resistant sample containers were developed.
• Spore samples were processed simultaneously in a high pressure vessel, ± pressure.
• HPT synergistically inactivates spores of B. amyloliquefaciens and C. sporogenes.

We sought to develop a paired sample container system that permits simultaneous processing of two samples in the same high pressure vessel, one pressurized and one protected by a pressure-resistant shell (heat-only), and subsequently compared the effect of pressure (600 MPa) on the inactivation of spores of Bacillus amyloliquefaciens and Clostridium sporogenes at high temperature. Reducing the compression rate to 200 MPa/min saw near-identical thermal profiles (R2 0.990) delivered to paired samples, thereby facilitating a means to directly attribute increases in inactivation in pressurised samples to the synergistic effect of pressure and heat. At 115 °C (3.5 min hold time), inactivation of B. amyloliquefaciens spores was around 7 log10 cfu/mL greater with pressure while the high pressure thermal (HPT) inactivation of C. sporogenes spores was approximately 2 log10 cfu/mL more than by heat alone after 1–2 min at 100 °C. Using this system we have demonstrated unequivocally that high pressure acts synergistically with heat to inactivate spores of B. amyloliquefaciens and C. sporogenes.Industrial relevanceTo facilitate commercialization of HPT processing for low-acid foods, a significant improvement in spore inactivation by HPT compared to traditional thermal processing, or HPT synergy, needs to be demonstrated. The development of a system that permits unequivocal assessment of the synergistic effect of pressure and heat on spore inactivation is an important tool to assist validating such processes.