Assessing the Pressure’s Direct Contribution to the Efficacy of Pressure-Assisted Thermal Sterilization

In pressure-assisted thermal sterilization process (PATS), most of the microbial inactivation occurs under a combination of high temperature and pressure conditions for which meaningful experimental isothermal/isobaric (static) survival data are rarely if ever available. Therefore, a kinetic survival model for the targeted microbe, the magnitudes of its parameters, and the pressure’s direct contribution to the process lethality, i.e., besides the processing temperature elevation, must be determined mathematically from experimental survival ratios obtained after the food cooling at the end of dynamic treatments. At least in principle, this can be achieved with the endpoints method, explained and demonstrated with the aid of simulated realistic dynamic temperature and pressure profiles. The pressure’s net (unmediated) contribution to the process lethality can be expressed as equivalent time at the processing temperature, or as the added number of decades’ reduction to the treatment’s final survival ratio had it been reached in a purely thermal process having the same temperature profile. The pressure’s role is also manifested in the coefficients of a special pressure dependency term incorporated into the dynamic inactivation kinetics model. This term indicates whether the process lethality rises monotonically with temperature and pressure or there exists an optimal combination of the two. The expanded rate model can be used to simulate and examine the efficacy of existing or contemplated PATS processes by varying the temperature and pressure profiles, and/or by modifying the targeted microbe’s survival parameters.