How can high pressure processing kill microorganisms like Listeria monocytogenes but not destroy meat structure?
A. While it’s tempting to think that high pressure “squashes” microorganisms like a person squashes a ripe tomato by stepping on it, that’s not really the case. In high pressure processing of food, the pressure is applied uniformly to the microbial cell – a marked contrast to the tomato example where the pressure is applied to the top of the tomato. Available evidence indicates that high pressure acts by inactivating microbial enzymes necessary for survival and multiplication and/or by increasing cell permeability and thereby disrupting transport activities used to maintain cell viability. Microbial cells have different cellular structures. Some microbial cells (e.g. Salmonella, E. coli O157:H7) are surrounded by only a thin membrane whereas others have an outer cell wall surrounding the membrane. Bacteria having only a cell membrane (sometimes called gram-negative bacteria) are more easily inactivated by pressure than those microorganisms that also have a cell wall (i.e. gram-positive
