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

Ramaswamy, Hosahalli S., Zaman, Shafi Ullah, Smith, James P.
Journal of food engineering 2008 v.87 no.1 pp. 99-106
slurries, Escherichia coli O157, kinetics, pathogen survival, fish products, plate count, food pathogens, Scomber scombrus, Listeria monocytogenes, high pressure treatment
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 10ml portions of stock culture in sterile plastic bags. Pressure treatments (250 and 400MPa for 0-60min) 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 350MPa, while a reverse trend was observed at lower pressures. The associated z p values indicated that the destruction rate of L. monocytogenes (z p =103MPa) was more sensitive to changes in pressure than E. coli (z p =185MPa). 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.