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 inac tivation of Escherichia coli O157:H7 NCTC 12079 and Staphylococcus aur eus NCTC 10652 in poultry meat and ultra-high-temperature-treated (UHT ) milk were investigated. The simultaneous application of high pressur e and mild heating was more lethal than either treatment alone. The su bstrate 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 degrees C resulted in approximately a 6.0-log(10) reduc tion in CFU/g in poultry meat and a 5.0-log(10) reduction in UHT milk; however, a <1-log(10) reduction was achieved with either treatment al one. In contrast, for S. aureus, a 15-min treatment of 500 MPa at 50 d egrees C was required to achieve a 5.0-log(10) reduction in poultry me at and a 6.0-log(10) reduction in UHT milk. As before, a <1-log(10) re duction in numbers was achieved with either treatment alone. The press ure-temperature inactivation curves of each organism, in each substrat e, were fitted using the Gompertz equation. Polynomial expressions der ived from the Gompertz variables were used to devise simple models whi ch predicted the inactivation of each pathogen at various pressure-tem perature combinations. Thus, a number of different pressure-temperatur e conditions could be chosen to achieve a desired inactivation level. The use of such models will provide flexibility in selecting optimum p ressure processing conditions without compromising microbiological saf ety.