Modeling of the microbial inactivation by high hydrostatic pressure freezing

• HPF is a novel application of High Hydrostatic Pressure treatment.
• HPF process is able to induce significant levels of microbial inactivation.
• The survival curves of the HPF treated cells may be described with the Weibull model.

This work aimed at investigating the effect of HPF processes on the inactivation kinetics of selected microbial strains, Escherichia coli O157:H7 ATCC 26 and Lactococcus lactis ssp. Cremoris suspended in McIlvine buffer. The effects of different processing conditions, namely pressure level (200–400 MPa), temperature (0, −10, −20 °C), treatment time (0, 2, 5, 7, 10 min) and number of phase transitions (single or multiple transitions) were investigated in the experimental trials. The mechanism of cell inactivation in complex processes, in which pressure and temperature are simultaneously changed, was also studied and the synergistic effect of the two processing parameters, if any, was identified. Experimental data were analyzed and fitted with mathematical models representing the kinetics of microbial inactivation in HPF processes.The results obtained so far demonstrated that the factor controlling the process efficiency is the pressure level at constant operating temperature. The level of inactivation obtained increased with decreasing the processing temperature at constant pressure or increasing the number of phase transitions, and with decreasing the size of ice crystals formed in the product. Finally, the kinetics of microbial death was described by a modified Weibull model, whose parameters are dependent on processing conditions.