What is High Pressure Processing?
High Pressure Processing (HPP) is a simple cost effective treatment that can make food safer to eat and extend shelf-life without reducing vitamin content and without altering flavour, texture or appearance. 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 as they cannot transmit the pressure through to the food. 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 pump is used to force more water into the vessel, creating hydrostatic pressure. The pressure is therefore transmitted through the water into the food.
The pressure is maintained for a pre-determined time (usually between 30 seconds and 15 minutes). During this time many food poisoning and spoilage bacteria are killed.
When the pressure cycle is complete, the vessel is depressurised, opened and the product 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, cod (dried and salted), shellfish, including oysters (sucked and in-shell), lobster and crab, cured ham, tapas selections, ready-to-eat meals, cooked and ready-to-eat meats, wet salads and dips, including coleslaw, salsas and houmous.
Selected references
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.
VALDRAMIDIS, V.P., GRAHAM. W.D., BEATTIE, A., LINTON, M., McKAY, A., FEARON, A.M. & PATTERSON, M.F. (2009) Defining the stability interfaces of apple juice: implications on the optimisation and design of high hydrostatic pressure treatment. Innovative Food Science & Emerging Technologies 10 (4) 396-404.
LINTON, M., MACKLE, A., UPADHYAY, V.K., KELLY, A.L. and PATTERSON, M.F. (2008) The fate of Listeria monocytogenes during the manufacture of Camembert-type cheese: A comparision between raw milk and milk treated with high hydrostatic pressure. Innovative Food Science & Emerging Technologies 9, 423-428
