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Fish Feed Research to Improve Protein Digestibility, Benefit Environment

25 August 2015

DENMARK - Scientists from Aarhus University and the industry have joined forces to improve feed for commercial fish farming in order to improve protein digestibility.

This can reduce the impact on the aquatic environment, improve fish growth and save the industry DKK 50 million a year.

Aquaculture is expanding at lightning speed and is the fastest growing food producing sector worldwide. For the fish to have optimum growth conditions their feed efficiency must match their needs.

Optimising feed efficiency is just what scientists and industry are collaborating on in a project funded by Innovation Fund Denmark.

Together with colleagues from University of Copenhagen, the Technical University of Denmark, and the fish feed producer BioMar, scientists from Aarhus University are participating in the project ExiPro, which aims at improving protein digestibility in fish.

Improved protein digestibility will increase fish growth, reduce the environmental impact and improve the economy of fish producers.

Feed is undoubtedly the most expensive variable cost and competition with production of feed for farm animals and pets means that protein is one of the most expensive ingredients in fish feed.

If the protein is not fully utilised then surplus nitrogen will end up in the aquatic environment. There is therefore every reason to optimise protein digestibility.

The project partners expect to increase protein digestibility by at least one per cent and protein intake by at least five per cent.

This means a total reduction of nitrogen excretion to the aquatic environment of at least nine per cent. Improved protein digestibility of one per cent may in itself help the industry save DKK 50 million a year in raw materials.

Optimising the extrusion process

The project aims at improving protein digestibility by optimising the specific part of feed production known as the extrusion process.

During this process the feed is heated and mechanically processed under high pressure – as a total mass – through an extruder (like when you squeeze toothpaste out of a tube), in order to achieve a final product with a specific homogenous form, which is suited for the specific fish and easy to handle.

The process involves heat and pressure, both of which may destroy the quality and digestibility of the protein. There is, however, limited knowledge about what happens to the protein during the extrusion process.

"The extruder is like a ”black box” as we only have limited knowledge on the chemical reactions and physical processes that take place in it," associate professor Trine Kastrup Dalsgaard from the Department of Food Science at Aarhus University, explained.

For scientists in her department, studies of protein-chemical changes are a core competence. ExiPro makes it possible to use this knowledge in relation to fish feed.

"We find it important to optimize the process and focus on raw material quality in order to minimize any damage to the protein during the processing of feed to achieve optimum fish feed and ensure high fish farming quality," Ms Kastrup Dalsgaard said.

The scientists are working together with co-workers to map the effects of extrusion on the physical and chemical properties of fish feed protein sources and examining how these changes affect fish growth, metabolism, protein intake, and nitrogen excretion.

This is performed by means of sophisticated biological methods such as oxidomics, peptidomics, and metabolomics, which can analyse changes in proteins, in vitro digestibility, and metabolism products, respectively.

An improved understanding of the extrusion process and its effects on feed protein will allow the project partners to develop extrusion tools for different protein feeds ensuring that each type of protein source will have the optimum treatment when producing feed.

TheFishSite News Desk



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