Text Box: 10:50 AM Text Box: MICROBIOLOGY Text Box: Influence of pressure rate and pressure pulsing on inactivation of Bacillus amyloliquefaciens spores during pressure-assisted thermal processing Text Box: Wannasawat Ratphitagsanti, Dr. Yousef, and Dr. Balasubramaniam Text Box: Pressure-assisted thermal processing (PATP) is an emerging food processing technology where a combination of pressure (500-700 MPa) and temperature (90-120°C) are employed to inactivate concerned microorganisms and enzymes. The objective of this study was to examine the role of pressurization rate and pressure pulsing in enhancing PATP bacterial spore lethality.  Bacillus amyloliquefaciens Fad 82 spore suspensions were prepared in de-ionized water at three inoculum levels (109, 108, and 106 CFU/ml), treated with two pressurization rates (18.1 and 3.7 MPa/sec), and held at 600 MPa and 105°C for 0, 0.5, 1, 2, 3, and 5 min. Experiments were carried out using custom-fabricated high pressure microbial kinetic testing equipment. Single and double pulses with the equivalent pressure holding time (1 and 3 min) were investigated. Spore survivors were enumerated by pour plating using trypticase soy agar after incubation at 32°C for 2 days. During short holding times (£2 min), PATP treatment with the slow pressurization rate provided enhanced spore reduction. However, the differences between pressurization rates diminished with extended pressure holding times. After 5 min, B. amyloliquefaciens population decreased 6.2 log regardless of pressurization rate and inoculum level. Double pulse treatment enhanced spore lethality by 2 to 4 logs compared to single pulse at a given pressure holding time. Closer examination of the pressure-temperature histories revealed that process temperature during second pulse was about 7-8°C higher than the first pulse, which might contribute to enhanced lethality. In conclusion, pressurization rate and multiple pulsing influence the efficacy of PATP treatment.