High pressure destruction kinetics of Escherichia coli (O157:H7) and Listeria monocytogenes (Scott A) in a fish slurry

High pressure (HP) destruction kinetics of Escherichia coli (O157:H7) and Listeria monocytogenes (Scott A) in mackerel (Scomber scombrus) were evaluated. Filleted fish were made into a slurry with peptone water and inoculated with the respective microbial strain to prepare a stock culture containing 106–107 CFU/ml. Samples were prepared for pressure treatment by heat-sealing 10 ml portions of stock culture in sterile plastic bags. Pressure treatments (250 and 400 MPa for 0–60 min) were given at room temperature (20–25 °C) in an isostatic press. Survival curves were established based on residual counts following treatment. Destruction kinetics were described as a dual effect, an initial destruction resulting from a pressure pulse (pulse effect) followed by a first order rate of destruction during the pressure holding time. E. coli was found to be more sensitive to pulse pressure than L. monocytogenes. Significant differences (p < 0.05) in high pressure resistance (D-value) were found between the two microorganisms. D-values of E. coli were higher than for L. monocytogenes at pressure levels ⩾350 MPa, while a reverse trend was observed at lower pressures. The associated zp values indicated that the destruction rate of L. monocytogenes (zp = 103 MPa) was more sensitive to changes in pressure than E. coli (zp = 185 MPa). Challenge studies with the more resistant pathogen, E. coli (107/ml), showed that a 10D treatment followed by refrigerated storage (4–12 °C) prevented its recovery/growth.