Interactions of high hydrostatic pressure, pressurization temperature and pH on death and injury of pressure-resistant and pressure-sensitive strainsof foodborne pathogens

The objective of this: study is to determine the interactions between high hydrostatic pressure, pressurization temperature, time and pH during pressu rization on death and injury of pressure-resistant and pressure-sensitive s trains of four foodborne pathogens: Staphylococcus aureus 485 and 765, List eria monocytogenes CA and OH2, Escherichia coli O157:H7 933 and 931, Salmon ella enteritidis FDA and Salmonella typhimurium E21274. Among these strains S. aureus 485, L. monocytogenes CA, E, coli O157:H7 933 and S, enteritidis FDA were reported to be more pressure-resistant than the respective strain of the same species (Alpas ct al., 1999). In general, viability loss of al l pathogens was enhanced significantly as the level of pressure and tempera ture were increased (P < 0.05). All the strains except S. aureus 485 demons trated more than 8 log cycle reduction when pressurized at 345 MPa at 50 de grees C for 5 min. This strain seemed to be the most pressure-resistant str ain within the conditions of the study. Pressurization in the presence of e ither citric or lactic acid increased the viability loss by an additional 1 .2-3.9 log cycles at pH 4.5 for both acids at 345 MPa. This study has indic ated that high hydrostatic pressure applied in conjunction with mild heat a nd acidity can be an effective method for inactivating pressure-resistant a nd pressure-sensitive strains of four foodborne pathogens in organic acid s olutions. This combination treatment indicates possible pressure pasteuriza tion applications to liquid feuds that have low pH. (C) 2000 Elsevier Scien ce B.V. All rights reserved.