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Technical attributes considered in selecting fish feed ingredients

Photo: Gunhild Haustveit©Nofima. NOFIMA ct-pellet-1024x295.jpg
The CT scan showed a large range in pore structure for pellets containing different amounts of tunicate meal.
Technical qualities of new feed ingredients often underestimated.

In the search for new, sustainable fish feed ingredients, researchers are working to see if the ingredients can be used in feed technically.

Tor Andreas Samuelsen and colleagues at Nofima in Bergen, Norway, have a number of advanced techniques in store. Samuelsen said it is underestimated the importance that new ingredients introduced to fish feed actually have the correct technical quality. Some ingredients require too much water; others require too high a temperature, while others disrupt the structural properties of the pellet.

“If you cannot produce feed with high physical quality, it will crush into pieces before it reaches the fish, and the fish will not be able to eat it,” Samuelsen said.

He has been investigating tunicate meal, which consists of dried and ground tunicates — a kind of sea squirt that feeds on microalgae in the sea. As part of the European Union's AQUABIOPRO-FIT and FutureEUAqua projects as well as the Swedish VINNOVA-funded project Marine Feed, the researchers have found that tunicate meal meets the nutritional requirements for ingredients that can replace some of the fish and soybean meal commonly used in feed, Nofima said.

Tunicate meal is rich in the essential amino acids fish need to build protein, but there’s still work to be done to reduce its salt content. Samuelsen has tested the technical quality of tunicate meal and how much can be used in the feed.

CT scans

Trial feeds were produced at the feed technology center in Bergen. First, feed mixtures with different levels of tunicate meal were fed into an extruder, where the mixtures were cooked, kneaded, expanded and dried into pellets with a porous structure. The pores were then filled with rapeseed oil and subjected to an oil leakage test.

Samuelsen used a computerized tomography (CT) scanner to examine the microstructure inside the pellet. A CT scanner is an advanced X-ray device that makes it possible to see the 3D structure without slicing the pellet, Nofima said.

“By studying the pellet’s inner structure, we gain a detailed understanding for example on how various ingredients affect the pore structure,” Samuelsen said.

The scan showed that feed pellets with a large percentage of tunicate meal had large pores. The pellet with the largest pores adsorbed the greatest amount of oil but also resulted in the most oil leakage, according to the announcement.

Determining the maximum

By running a mixture design experiment in the statistics program, Samuelsen has set some quality requirements for the pellet when he adds tunicate meal to the feed.

“I want as much tunicate meal as possible in the feed mixture, but the pellet still needs to be of high physical quality and as porous as possible to make it adsorb the necessary quantities of oil. It also needs to have a high-water stability,” Samuelsen said.

He found that 50% of the fish meal could be replaced by tunicate meal without compromising the physical quality of the feed.

Advanced tools

New ingredients that may be interesting to use in fish feed are constantly emerging. The work on tunicate meal is an example of how important it is to have advanced tools for studying ingredients and feed, Samuelsen said.

“We need to understand why ingredients differ from each other to be able to model the production process and physical properties of the feed before we start,” he added.

Such new tools are now available through the Aquafeed Technology Centre (ATC), which is hosted by Nofima. This is part of the Norwegian roadmap for research infrastructure, which is carried out in cooperation with Norce and the University of Bergen. ATC provides the industry with access to state-of-the-art laboratories and pilot-scale facilities to be able to meet the future needs of research, process and product development.

“ATC gives Nofima a unique opportunity to help the industry develop and characterize new sustainable ingredients,” Samuelsen said.

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