The effect of high hydrostatic pressure on Listeria monocytogenes in phosphate-buffered saline and model food systems

Three strains of Listeria monocytogenes (NCTC 1194, a poultry isolate and the Scott A strain) were exposed to a range of pressures (300, 350, 375, 400 and 450 MPa) in 10 mmol 1(-1) phosphate-buffered saline (PBS) at pH 7.0 for up to 30 min at ambient temperature. Generally, increasing the magnitude and duration of compression resulted in increasing levels of inactivation, although the inactivation kinetics varied depending on the strain and pressure applied. The three strains also exhibited a wide variation in their resistance to high pressure. The resistance of the three strains to high pressure (375 MPa) was also assessed in a series of model food systems containing one of each of the three main food constituents: protein (1, 2, 5 and 8% w/v bovine serum albumin in PBS), carbohydrate (1, 2, 5 and 10% w/v glucose in PBS) and lipid (olive oil (30% v/v) in PBS emulsion). Overall, increasing the concentrations of bovine serum albumin (BSA) and glucose in the suspending medium resulted in decreasing levels of inactivation of all three strains; however, the minimum concentration of BSA and glucose required to increase survival to a level greater than that observed in PBS alone varied depending on the strain and on the duration of the treatment. The survival of all three strains was greater in the olive oil/PBS emulsion than in PBS alone at all treatment times.