INTERACTION OF HYDROSTATIC-PRESSURE, TIME AND TEMPERATURE OF PRESSURIZATION AND PEDIOCIN ACH ON INACTIVATION OF FOODBORNE BACTERIA

High hydrostatic pressure, because it can kill microorganisms, is bein g investigated for potential use as a nonthermal food preservation met hod. The objective of this study was to determine the hydrostatic pres surization parameters, pressure, time, and temperature, and a bacterio cin that in combination would destroy 7 to 8 log cycles of pathogenic and spoilage bacterial populations. We suspended cells of Staphylococc us aureus, Listeria monocytogenes, Salmonella typhimurium, Escherichia coli O157:H7, Lactobacillus sake, Leuconostoc mesenteroides, Serratia liquefaciens, and Pseudomonas fluorescens in peptone solution and exp osed them to the combination of treatments. The combined parameters us ed were hydrostatic pressure (138 to 345 MPa), time (5 to 15 min), tem perature (25 to 50 degrees C), and pediocin AcH (3,000 AU/ml, final co ncentration). In general, cell death increased as the pressure, time, or temperature increased; however, the cells developed proportionately greater sensitivity as the pressure increased to 276 MPa and higher a nd the temperature increased above 35 degrees C. Pressurization for lo nger than 5 min, especially at lower pressure and temperature ranges, had very little added benefit. Among the four gram-negative species, E . coli O157:H7 was the most resistant to pressurization while among th e four,sram-positive species, L. sake and L. mesenteroides had greater resistance. The death rate at high pressure (345 MPa) and high temper ature (50 degrees C) in combination followed first-order kinetics; at a lower pressure and temperature combination it showed a late tailing effect. Estimated D value data indicated that even at 345 MPa and 50 d egrees C an 8-log-cycle viability loss could not be achieved within 5 min for all eight species. However, when pediocin AcH was included dur ing pressurization this loss was achieved.