Proteins from Sea Buckthorn useful in food production

Atle Kjærvik
Photo: Gøril Klemetsen

Researchers from Trondheim have worked with the Swiss company Nestlé on a patent for the use of certain proteins in buckthorn, controlling the formation of ice in the plant's berries. These proteins, called ice nucleators, can be used in the production of food and beverages.

Buckthorn forms thickets as here by the Nidelva river in Trondheim. Researcher Rolv Lundheim shows the tiny, reddish-orange fruits from the bush which contains a lot of vitamin C.

''Ice nucleators speed up the freezing process. The nutrient industry can make use of buckthorn proteins in the production of freeze-dried coffee and juice, as well as in ice cream and concentrated soya proteins'', says researcher Rolv Lundheim at Allforsk's Department of Ecotoxicology.

Ice nucleators have long been used in machines which produce 'artificial' snow, but they have never been used in commercial food production.

Sea buckthorn was chosen

Lundheim recently completed his PhD at NTNU on the topic of ice nucleators and anti-freeze proteins (peptides). Anti-freeze substances regulate, among other things, the defrosting process. Lundheim is one of those responsible for the Nestlè patent, which took seven years to approve.

Lundheim's task was to investigate a wide range of animals and plants in order to find and prepare ice nucleators which Nestlè would be able to use. After a while Lundheim decided to concentrate on sea buckthorn, mussels, seaweed and kelp. His work showed that substances which have completely different purposes from that of promoting the formation of ice, can also serve as ice nucleators.

'Nestlè chose buckthorn because the plant had already gained international acceptance as a nutrient, and because its berries are easy to obtain all over the world. Large crops are for example grown in Eastern Europe and China', says Lundheim.

Controlling the formation of ice

Ice nucleators and anti-freeze proteins are very important for organisms which have to survive at low temperatures. Ice nucleators control the formation of ice and prevent water from becoming super-cooled before it freezes. Such nucleators are found in many plants and organisms, such as sea buckthorn fruits, mussels, seaweed and kelp, as well as in certain insects. The anti-freeze proteins are found, among other places, in insects and in fish.

When water or watery solutions freeze, they normally supercool to a temperature much lower than zero degrees centigrade before the water itself freezes. But for many industrial processes, such as freeze-drying, supercooling is not advisable. Instead, it is desirable that the formation of ice take place at as high a temperature as possible.Thus, it is possible to save energy, for instance by adding fruit sap from the buckthorn containing a ice nucleator.

Preserving aromatic substances

Freeze concentration means that water (in the form of ice) is removed from the food item, while the remaining soluble substances are retained in concentrated form in the water which is left.

This way of concentrating food products means that taste substances are better preserved. The method is often used for the conservation of fruit, berries, and juice. Ice nucleators create larger ice crystals, which ensure more efficient separation of ice and liquid.

When more appealing structures are required in certain vegetable protein concentrates, these are frozen. Large crystals ensure better structures, providing, for example, soya protein concentrates with a consistency not unlike that of meat.

Preventing recrystallisation

Among other things, anti-freeze proteins are able to prevent the process of recrystallisation from taking place in frozen food. When recrystallisation takes place, larger crystals 'devour' the smaller ones, so that the food item becomes full of unpleasantly large and conspicuous crystals.

This happens regularly with ice cream which has been kept at too high a temperature. The same process can also take place in other foods, and leads to a substantial 'drip-loss' meaning that the water contained in the food drains off when the food is thawed, so that it tends to be dry when prepared.

Anti-freeze proteins have not been used in the food-production industry, but recently Allforsk also has helped Nestlè register a patent for using proteins such as these which have been obtained from fish in food products.

Gemini fakta

Two strategies for handling cold
Animals and plants have two main strategies to allow them to survive in the cold.
The first is to prevent themselves from freezing by means of anti-freeze peptides (short proteins). Anti-freeze peptides are 'glued' to the outside of already existing ice crystals, a process which prevents any further formation of ice.
The other strategy is that of tolerating a frozen condition by controlling the freezing process by means of ice nucleators.
Ice nucleators form the nuclei of large ice crystals. Such proteins control the freezing process at certain temperatures and ensure that the freezing process takes place outside the cells and in body cavities that can tolerate expansion.