High Pressure Processing
It can be carried out at room temperature and the pressure used is immense (up to 600 Mega Pascals (~90,000 psi). The pressure is transmitted through water, which completely surrounds the packaged food. As the pressure is equally distributed, there is no obvious crushing effect.
How are foods pressurised?
Foods are pre-packaged in either a vacuum-pack bag or in a flexible plastic bottle. Hard materials such as glass or metal cannot be used. The packaging must be able to withstand a volume change of up to 15%, followed by a return to its original size, without losing seal integrity or barrier properties.
The packaged items are placed in the pressure vessel. The vessel is sealed and filled with water. A pressure intensifier pumps pressurised water into the vessel, creating hydrostatic pressure. The pressure is therefore transmitted via the water into the food. The pressure applied is uniform and instantaneous regardless of the size and shape of the food. The pressure is maintained for a pre-determined time (usually between 30 seconds and 15 minutes).
During this time most of the food poisoning and spoilage microorganisms are killed. When the pressure cycle is complete, the vessel is depressurised almost instantaneously. The vessel is opened and the product may then be removed.
What types of food can be pressure-treated?
HPP is suitable for foods that have a high water content. It is particularly useful for raw foods, when retention of fresh characteristics is important, as the treatment does not significantly alter flavour, texture or appearance. HPP products that are commercially available worldwide include fruit juices and smoothies, fruit purees, jams and jellies, avocado halves and guacamole, shellfish (including oysters, lobster and crab), cured ham, tapas selections, ready-to-eat meals, cooked meats, wet salads and dips (including coleslaw, salsas and hummus).
Patterson, M.F., McKay, A., Connolly, M. and Linton, M. (2010) Effect of high pressure on the microbiological quality of cooked chicken during storage at normal and abuse refrigeration temperatures. Food Microbiology 27: 266-273.
Patterson, M.F. and Linton, M. (2008). Factors affecting inactivation of foodborne bacteria by high pressure. In: High Pressure Microbiology, (Eds. C.W. Michiels, A Aersten, D.H. Bartlett and A. Yayanos), ASM press, USA. pp: 181-193.
Patterson, M.F., Linton, M. and Doona, C.J. (2007). Introduction to high pressure processing of foods. In: High Pressure Processing of Foods, (Eds. C.J. Doona, C.P. Dunne and F.E. Feehery), Blackwells Publishing, Iowa, USA. pp: 1-14.