The Combined Effect of High Hydrostatic Pressure and Mild Heat on Inactivation of Pathogens in Milk and Poultry

The combined effects of high hydrostatic pressure and heat on the inactivation of Escherichia coli O157:H7 NCTC 12079 and Staphylococcus aureus NCTC 10652 in poultry meat and ultra-high-temperature-treated (UHT) milk were investigated. The simultaneous application of high pressure and mild heating was more lethal than either treatment alone. The substrate was found to have a significant effect on the survival of the pathogens during treatment. For E. coli O157:H7, a 15-min treatment of 400 MPa at 50°C resulted in approximately a 6.0-log10 reduction in CFU/g in poultry meat and a 5.0-log10 reduction in UHT milk; however, a < 1-log10 reduction was achieved with either treatment alone. In contrast, for S. aureus, a 15-min treatment of 500 MPa at 50°C was required to achieve a 5.0-log10 reduction in poultry meat and a 6.0-log10 reduction in UHT milk. As before, a <1-log10 reduction in numbers was achieved with either treatment alone. The pressure-temperature inactivation curves of each organism, in each substrate, were fitted using the Gompertz equation. Polynomial expressions derived from the Gompertz variables were used to devise simple models which predicted the inactivation of each pathogen at various pressure-temperature combinations. Thus, a number of different pressure-temperature conditions could be chosen to achieve a desired inactivation level. The use of such models will provide flexibility in selecting optimum pressure processing conditions without compromising microbiological safety.