Inactivation and injury of pathogens on intact beef treated with hydrodynamic pressure

The effect of hydrodynamic pressure (HDP) treatment on the inactivation of Escherichia coli O157:H7, Salmonella Typhimurium, and Listeria monocytogenes attached to beef surface was evaluated. Irradiated beef cubes were inoculated with these individual pathogens (ca. 4 log CFU.g−1) and treated with HDP. Surviving populations of E. coli O157:H7, S. Typhimurium, and L. monocytogenes were determined by spiral-plating on Sorbitol MacConkey agar (SMAC), XLT4 agar, and modified Oxford (MOX) agar, respectively. The HDP treatment significantly reduced E. coli O157:H7 (0.75 log CFU.g−1), S. Typhimurium (1.09 log CFU.g−1), and L. monocytogenes (0.55 log CFU.g−1) from beef surfaces. HDP-induced injury as determined by plating on non-selective media revealed that ca. 0.5 log CFU.g−1 of E. coli O157:H7 and S. Typhimurium cells were injured. Most cell injury occurred at the cell membrane level as observed by transmission electron microscopy (TEM).Industrial relevanceResults obtained in the present study show that HDP treatment, primarily evaluated for meat tenderness improvement, also reduces the number of viable pathogens attached to beef surface. Additional hurdle treatment will be helpful to further reduce pathogens on beef surface.

► HDP treatment reduced up to 1 log CFU.g−1S. Typhimurium attached to beef surface.
► Approx. 0.5 log CFU.g−1 cells of E. coli O157:H7 and S. Typhimurium got injured during the treatment. The treatment resulted in sublethal injuries, such as cytoplasmatic membrane invagination and in lethal injuries, such as collapse of the cell wall and hypercondensation of the cytoplasm.