THE EFFECT OF HIGH HYDROSTATIC-PRESSURE ON LISTERIA-MONOCYTOGENES IN PHOSPHATE-BUFFERED SALINE AND MODEL FOOD SYSTEMS

Three strains of Listeria monocytogenes (NCTC 11994, a poultry isolate and the Scott A strain) were exposed to a range of pressures (300, 35 0, 375, 400 and 450 MPa) in 10 mmol 1(-1) phosphate-buffered saline (P BS) at pH 7.0 for up to 30 min at ambient temperature. Generally, incr easing the magnitude and duration of compression resulted in increasin g levels of inactivation, although the inactivation kinetics varied de pending on the strain and pressure applied. The three strains also exh ibited a wide variation in their resistance to high pressure. The resi stance of the three strains to high pressure (375 MPa) was also assess ed in a series of model food systems containing one of each of the thr ee main food constituents: protein (1, 2, 5 and 8% w/v bovine serum al bumin in PBS), carbohydrate (1, 2, 5 and 10% w/v glucose in PBS) and l ipid (olive oil (30% v/v) in PBS emulsion). Overall, increasing the co ncentrations of bovine serum albumin (BSA) and glucose in the suspendi ng medium resulted in decreasing levels of inactivation of all three s trains; however, the minimum concentration of BSA and glucose required to increase survival to a level greater than that observed in PBS alo ne 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 e mulsion than in PBS alone at all treatment times.