High pressure treatment leads to better berries

Raspberries can be kept for more than 90 days if they are treated with high pressure. Photo: Lidunn Mosaker Boge/Nofima

Scientists at Nofima have during the past three years been exposing food to extremely high pressures, to determine whether the pressure treatment gives healthier, safer and more tasty food. Berries are one food for which the treatment is successful.

Here are the facts:

Food in the shops has often been heat treated to eliminate bacteria and increase its shelf life.

The heating process causes some foods to lose quality. By exposing the food to high pressure (2,000-6,000 bar) it is possible to inactivate microorganisms without using heat. The method is extremely gentle, and can be combined with mild heat treatment.

Scientists at Nofima have during the past three years been exposing food to extremely high pressures, to determine whether the pressure treatment gives healthier, safer and more tasty food. Berries are one food for which the treatment is successful.

“Raspberries, both whole berries and crushed berries, can be kept for more than 90 days. And strawberry purée keeps its nice fresh character for a long time. This gives good opportunities for developing new products,” says scientist Tone Mari Rode.

She has led the research, which has been carried out in close collaboration with the food industry. Exposing food to high pressure is a relatively new method, and the Norwegian food industry has not yet made the investment that is necessary to start using it.

Nofima has experienced a high demand from industrial actors who want to try the new technology. Several projects have allowed food producers to test whether their products can be improved by high pressure processing, and whether it is possible to develop new products. Many different types of meat, vegetables, dairy products, fruit and berries have been given high pressure treatment, and the scientists have learned a great deal.

A different taste – with precipitation

“High pressure juice tastes wonderful, and some types taste better than normal freshly squeezed juice. And it keeps its high quality longer than the freshly squeezed juice that you can buy today,” says Rode.

Normal juice is given a rapid heat treatment before being cooled. This increases its shelf life, but the taste of the juice changes in the process.

Scientists for this reason decided to investigate whether high pressure treatment can give newly squeezed juice longer shelf life, and thus make it more flexible in the market.

“Even if the juice keeps fresh longer, some precipitation will eventually fall out in the bottles. This is produced by natural enzymes in the berries. You see this also in freshly squeezed juice, and the high pressure does not inactivate all of these enzymes, as heat treatment does.”

It’s not as well-known in Norway that precipitation is a sign of high quality as it is in other countries, where it is seen as natural, and people are used to shaking the bottle. If producers are going to invest in new products, they will have to come to a decision about whether consumers are willing to accept more precipitation.

Nofima scientist Tone Mari Rode demonstrates high-pressure treatment to give raspberry juice considerably longer shelf life. Photo: Lidunn Mosaker Boge/Nofima

Samples to win over sceptics

Scientist Nina Veflen Olsen has studied how Norwegian consumers view new technology. She has seen that many people are sceptical to methods that they know little about.

“The best thing is to let people taste the product. If they like the taste, the chances are good that they will buy it,” she says.

Olsen points out that it’s also important to inform consumers about the advantages for them, when introducing a new product. More knowledge can contribute to building up a positive view of the new technology, and the most important source of knowledge is experience.

Acceptance of the high pressure method compares well with that of other new technologies. Consumers do not have any immediate negative associations when told that high pressure has been used.

Small details for success

Not all products are equally suitable for high pressure processing. Raw fish and raw meat have proved to be less suitable, but some marinated raw meat products that have been treated with high pressure are available on the European and American markets. Oysters are another great success in the US.

Dry fermented meat products and marinated meat have achieved the best results in Nofima’s test of meat products. These types of product, however, can also face challenges in high pressure treatment and the result can range from a rancid product to one with fantastic quality.

“The food industry has much to gain from using high pressure during production, but small adjustments during product development are very important. The taste, appearance or shelf life can change significantly simply by exchanging a type of oil or spice. This means that it is crucial to test various conditions for individual products,” says Tone Mari Rode.

It’s not possible to conclude that the method works well or not with a group of foods, and each individual product must be tested separately.

The scientists suggest that high pressure technology is best suited for “premium” products, where the consumer is willing to pay a higher price to obtain a product that has been treated mildly, and thus retained its high quality.

Better use of excess berries

Tone Mari Rode and her colleagues are working on several projects in high pressure treatment. They will examine, in collaboration with fruit and berry producers in Rogaland, Hordaland and Sogn og Fjordane, whether the high pressure technology can lead to better use of fruit and berries that cannot be sold through conventional retail channels.

The Norwegian growing season is relatively short, so the aim is to discover whether excess fruit and berries, or those of lower quality, can be used in new products with higher prices, after being subjected to high pressure.

“The fruit and berry industry is very interested in this, and it’s clear that they are aware of the potential,” says Rode.

The projects have been financed by the Research Council of Norway and the Vestlandet Regional Research Fund.

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