© Gunhild Haustveit, Nofima
Tor Andreas Samuelsen and colleagues at Nofima in Norway are assessing whether a variety of the novel ingredients being introduced to fish feed - such as tunicate meal - actually have the correct physical qualities. 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 be crushed into pieces before it reaches the fish, and the fish will not be able to eat it,” says Samuelsen.
One of the ingredients he is assessing is protein made up of dried and ground tunicates; a kind of sea squirt which feeds on microalgae. As part of the EU projects AQUABIOPRO-FIT and FutureEUAqua, 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.
Tunicate meal is rich in the essential amino acids that fish need to build protein, but there’s still a 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.
Feed analysis with a CT scanner
Trial feeds were produced at the Aquafeed Technology Centre (ATC) 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 then subjected to an oil leakage test.
Samuelsen used a CT scanner to examine the microstructure of the pellet.
“By studying the pellet’s inner structure, we gain a detailed understanding for example of how various ingredients affect the pore structure,” he says.
The scan showed that feed pellets with a large percentage of tunicate meal had large pores. The pellet with the largest pores adsorbed the highest amount of oil, but also resulted in highest oil leakage.
Determining the maximum amount of tunicate meal
By running a mixture design experiment in the statistics programme, he 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,” he explained.
Samuelsen found that 50 percent 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 a nice example of how important it is to have advanced tools for studying ingredients and feed, says Samuelsen.
“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.”
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 characterise new, sustainable ingredients,” he adds.
