Factors influencing death and injury of foodborne pathogens by hydrostatic pressure-pasteurization

The key objective of hydrostatic pressure-pasteurization of food is the destruction of pathogenic bacterial cells at a high level (8log cycles) without adversely affecting the acceptance characteristics of a food. To achieve these goals, hydrostatic pressure-pasteurization may best be conducted at a moderate pressure, which alone will not kill the desired level of pathogens. However, along with hydrostatic pressure other parameters, namely pressurization-time, temperature and bactericidal compounds, such as bacteriocins, can be used to enhance bactericidal effects of pressurization.Our results with four pathogens indicated that viability loss at 25°C were minimal up to 207MPa, then increased at a rapid rate. However, even above 483MPa, not all species had 8log cycles viability loss. At and above 276MPa a large number of survivors were injured. At 207MPa and 25°C, pressurization for 30min did not greatly enhance viability loss and injury of the four pathogens. However, pressurization temperatures beyond 35°C greatly increased cell death and injury. By pressurizing the cells in the presence of a mixture of pediocin AcH and nisin viability loss of the pathogens was increased by an additional 1.3 to 5.1log cycles. This increase was due to the bactericidal effect of the two bacteriocins on sensitive and injured cells. These results indicated that at moderate pressure, a high level of destruction of pathogens can be induced within a short time by using moderate temperature in combination with bactericidal preservative(s).