A mild preservation technology, for both pasteurization and sterilization, where vitamins, natural colourings and flavourings are preserved. The cell wall, cell membrane and membrane surrounding the nucleus of micro-organisms break down and unwanted substances can penetrate.
Preserving by ultra-high isostatic pressure is a mild preservation technique. With high pressure foods can be sterilized as well as pasteurised, while vitamins, natural colourings and flavourings remain intact. In addition, changes can be made to macromolecules, such as crystallizing of lipids, denaturation of proteins and enzymes and gelatinization of starch.
Mainly acidic products can be conserved by ultra-high isostatic pressure. In this case, the vegetative micro-organisms are killed by the high pressure and a low pH prevents outgrowth of spores. Among other things fruits, fruit juices, jams, guacamole (avocado mousse), rice and fish can all be preserved with this technique. In addition, the technique is used to change the texture of meat and fish. Products that contain air often lose their structure. The air in the product is in fact pressed out by the pressure.
Description of Technique
In advance the product to be treated is packed in a container which is compressible. The packaged product is placed in a pressure chamber, similar to an autoclave. The pressure chamber is filled with a high pressure liquid. For this purpose in the current equipment mostly water is used with a small amount of soluble oil for the necessary lubrication and corrosion prevention. With the aid of a plunger pump, a very high pressure - between 2,000 and 10,000 bar - is generated, which is passed through the high fluid pressure to the (packaged) foodstuff. After a treatment time of 1 to 15 minutes, depending on the product, the pressure is released.
The applied pressure is isostatic, so that the pressure is uniformly propagated throughout the entire product. The temperature of the treated foodstuff increases to a maximum of 25°C by the energy input via the high pressure. If this temperature rise is undesirable, cooling of the pressure chamber is possible.
The continuous introduction of goods in a high-pressure area is difficult, so the treatment is being applied batch-wise at the moment.
Due to the high pressure the cell wall, cell membrane and membrane around the cell nucleus of micro-organisms are broken or become permeable, so that undesirable substances may get into the cell. The following pressures are applied:
- Killing vegetative bacteria and protein denaturation: 4,000 - 6,000 bar (5 - 25°C)
- Denaturation enzymes: 3,000 - 8,000 bar
- Inactivation bacterial spores: 10,000 bar (80°C)