Effect of Hydrostatic Pressure on the Induction and Inactivation of Bacterial Spores Phase 1

Abstract : Destruction of microbial cells and bacterial spores by hydrostatic pressure is being envisioned as a nonthermal novel technique in food preservation. A combination of 50000 psi (345 MPa) at 50C could kill over 6 log cycles of foodborne pathogenic and spoilage bacteria within 5 min. In contrast, even 200,000psi at 80C for 60min will not be able to inactivate important bacterial spores to the same level. However, bacterial spores can be induced to germinate at a relatively low pressure range, and then the germinated and over-growing spores can be destroyed by one or more methods used in destroying the bacterial cells. To achieve this goal it would be necessary to determine the pressurization parameters that would induce maximum germination of spores. In the Phase I study, the frequency of germination induction of 2 Bacillus and 4 Clostridium species (that include both food spoilage and pathogen) following exposure to several pressurization-temperature combinations was examined. Depending upon a treatment, pressurization-temperature combinations caused both inactivation and induction of spores, which were some what directly proportional; but the Bacillus spores were more sensitive than the clostridial spores. The pressurized spores continued to germinate during subsequent storage with higher germination at 25C that at 4C as determined by the increase in inactivation by low heat treatment.