New processing method increases the potential for using plant-based ingredients in fish feed

Birger Svihus

The access to marine resources as ingredients in fish feed is becoming increasingly limited. In addition, from the perspective of product quality, it is also desirable to increase the share of plant-based ingredients in fish feed – both because this strategy is more sustainable and because the contents of environmental toxins such as PCBs and dioxins are lower in plant-derived ingredients.

Lakseoppdrett Foto: Karin Beate Nøsterud

However, farmed species such as salmon, trout and cod are carnivores and could react negatively to vegetable ingredients, e.g., soybeans and rapeseed. One reason for such reactions is the content of certain biological components, so-called antinutrients, in plant-based raw materials. These antinutrients can cause problems for the fish, e.g., poor digestion. For warm-blooded animals, this problem was solved by adding enzymes to the feed. When an animal ingests the feed, the enzymes destruct the antinutrients. Due to the low temperatures in the fish gut, the use of enzymes in this way does not have the same effect on cold-water species such as salmon, trout and cod. Furthermore, the temperature in the extrusion process is so high that the enzymes are easily destroyed during feed production.

Research performed at the Aquaculture Protein Centre has shown that by including an additional step in the feed production process, it is possible to enzymatically degrade undesirable substances in the feed before it is exposed to the high temperatures in the extrusion process. The result is a feed with about the same production cost, but with an improved nutritional value and a higher application potential in the fish farming industry. The process also enables the use of a considerably larger share of plant-based feed ingredients. Pilot trials performed at the Centre for Feed Technology showed that this method can reduce the contents of the antinutrient phytic acid by 80 percent. In the process, water and enzymes are added to the ingredients to be treated. The amount of water, pH, temperature and the length of the treatment are optimized for maximum degradation in an integrated production process, in which the feed is conditioned and extruded as usual after the enzyme treatment. A patent application has been submitted for this processing method.


Updated: 13.03.06
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