54F-14

S. PANDRANGI, S. Rajan, V. M. Balasubramaniam, and A. E. Yousef. Dept. of Food Science & Technology, Ohio State Univ., 2015 Fyffe Ct., 110 Parker Food Science Bldg., Columbus, OH 43210-1007

Pressure-Assisted Thermal Processing (PATP) can be successfully used to manufacture shelf-stable low-acid foods. However, kinetics of spore inactivation by PATP have not been extensivley investigated. The objective of this study was to determine kinetic parameters for the inactivation of selected Bacillus spores by PATP, compared with these obtained during thermally processing. Spores of Bacillus stearothermophilus ATCC 7953, B. polymyxa ATCC 21993 and B. subtilis OSU 494 were tested in this study. Water suspensions of these spores (10⁸ spores/mL) were heated to a predetermined temperature and then pressure-heat treated at 700 MPa and 70^o C to 105^o C. Pressure holding times ranged from 0-5 minutes. Thermal inactivation of these spores was conducted at 100^o C to 121.1^o C. Viable spores in processed samples were enumerated on plate count agar after incubation for 48 hours at 37^o C for B. polymyxa and B. subtilis or 55^o C for B. stearothermophilus. In case of pressure treated samples, spores were enumerated with or without heat shocking at 80^oC for 30 min. Transmission Electron Microscopy (TEM) images of treated spores were obtained to compare the nature of damage caused by different treatments. PATP accelerated the inactivation for all spores when compared to the thermal treatment alone. Decimal reduction (D_121.1C and D_{700Mpa, 105C}) values for B. stearothermophilus were 5.2 + 1.5 and 0.29 + 0.00 min, respectively. For B. polymyxa D₁₀₀ and D_{700Mpa, 90C} were 2.5 + 0.5 min and 0.22 + 0.004 min, respectively. Similarly, D_100C and D_{700Mpa, 70C} for B. subtilis were 2.3 + 0.2 and 0.34 + 0.01 min. Heat shocking did not seem to contribute to the lethality of PATP, with the exception of B. polymyxa where heat shocking caused an addition one log reduction. TEM images showed more profound damage to the core of certain spores due to PATP treatment. Among the Bacilli spp. tested, B. stearothermophilus seems to be the most PATP resistant. Combinations of pressure and heat have a strong lethal action against spores of Bacillus spp.

Session 54F, Nonthermal Processing: General I
2:00 PM - 5:30 PM, Monday PM Room Hall I-2

2005 IFT Annual Meeting, July 15-20 - New Orleans, Louisiana