High pressure-high temperature sterilization: From kinetic analysis to process verification

The inactivation of Clostridium sporogenes PA 3679 spores by high pressure at high temperatures (HP-HT) in phosphate buffer was investigated in a lab-scale temperature-controlled HP system (QFP-6) with an internal heater to maintain the sample temperature. Some inactivation of spores occurred during the pressurization come-up time (CUT) and depressurization time. The inactivation of PA 3679 was found to be exponential during the adiabatic holding period of the HP cycle at constant pressures and temperatures. The inactivation rate increased with both pressure and temperature. The kinetic parameters - such as D-values at tested temperatures and pressures that are necessary for the design of process parameters of HP sterilization process - were determined. Within the pressure range of 600-800 MPa, the calculated D-values ranged from 270.3 to 357.4 and 49.0 to 67.6 s at 91 and 108C, respectively. These studies provided basic data on the effects of pressure and temperature on the inactivation of PA 3679 spores under conditions applicable to the development of preservation specifications for commercial HP-HT processing of low acid foods. The spore strips of C. sporogenes were used as indicators for microbiological verification of delivered lethality of HP-HT sterilization process at different processing conditions in a pilot scale HP vessel.