Increasing the pressure for extended shelf life
Extending shelf life, better utilisation and less use of preservatives are just some of the advantages of the high pressure treatment of food.
“Producing food with a longer shelf life without traditional heat treatment or additives is many food producers’ dream. The fact that high pressure treatment can also help to improve utilisation, raise quality and achieve healthier and fresher food makes this an exciting focus area for our research,” says Morten Sivertsvik, Nofima’s research manager in Stavanger.
Allows for product innovation
No Norwegian food producers are currently using high pressure processing, mainly because the equipment is still very expensive to purchase. Internationally, on the other hand, more and more producers are getting involved and the method is being used as a sales point.
Pates, ready meals, purees, juices and sliced meats are among the high-pressure treated foods already on the market. The method also allows for completely new kinds of foods, because we can create new structures and properties.
“We started using our high pressure equipment in September, and when we bought it we set up a partnership agreement for further development with the equipment producer Avure. Food producers who want to test the equipment are therefore very welcome to run tests here,” concludes Sivertsvik. “A workshop will be held at Måltidets Hus on 19 January 2011for the industry to learn more about the equipment and try it out in practice,” explains Sivertsvik.
Safer, healthier and fresher food
High pressure processing deactivates unwanted bacteria and increases shelf life, without using additives. This is the method’s most important advantage and fits well with market trends. As consumers, we are increasingly demanding fresher and more natural food without additives.
Another great advantage of high pressure processing is that the food retains its original nutritional value, while the sensory properties can be changed depending on how the raw materials are handled. This gives a product with a fresher colour and a more natural flavour. High pressure processing of lobster and crab, for example, also improves the utilisation of the flesh, because the pressure helps to loosen it from the shell. Oysters become easier to open for the same reason, while bacteria and viruses inside the shell are killed and shelf life increased. High-pressure processed raw oysters, with an extended shelf life, can be found in foreign markets.
High pressure processing is also positive for the environment, both because the increased shelf life could reduce waste, and also because the process uses less energy than traditional heat treatment.
Faster, more homogenous heating
The high pressure equipment now at Nofima is a laboratory version, with the possibility of combining heat and high pressure. Maximum pressure is 6,900 bar and maximum temperature 90°C. Because pressure cooking itself also raises temperatures somewhat, it is possible to achieve final temperatures well over 100°C.
The advantage of combining heat and pressure is that one can achieve pasteurisation or sterilisation combined with pressure treatment. In this way spores, for example, can be deactivated. In other cases the use of pressure alone is more relevant.
With the high pressure process, the product is placed in a steel container and water is used to create the high pressure. Unlike heat treatment, where the product is heated up gradually, the high pressure gives an immediate and homogenous effect throughout the product. Pressure is applied for a fixed period, usually between 1 and 20 minutes, and the short time required to come up to the desired pressure means that the process takes considerably less time than traditional heat treatment.
“The use of high pressure equipment is a natural extension of the work we have done in heat treatment,” say Nofima researchers Maria Befring Hovda and Tone Mari Rode. They have carried out tests using salmon fillet to find out how it is affected by different pressures. Other products, including halibut, tomatoes and mange tout peas have also been tested. Tests have also been made with Listeria to see how this bacterium is affected by extreme pressure. The effect of high pressure on Bacillus spores will also be tested in the near future.
The pressure that can be achieved in the high pressure equipment is not found anywhere in nature. The highest natural pressure is found in the Marianas Trench in the Pacific, the world’s deepest ocean trench, some 11,034 metres below the surface at its deepest. The pressure here is about 1,000 bar. The pressure in the high pressure equipment can be seven times greater. For comparison, 4,000 bar is like the pressure of 26 cars on a postage stamp.