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How Does Time of Slaughter Affect Texture and Whiteness of Cod Fillet?

27 September 2013
© Nofima (formerly Fiskeriforskning)

NORWAY - By using the experimental swim tunnel at the Tromsø Aquaculture Research Station, scientists hope to find out when trawl captured cod should be slaughtered in order to obtain the whitest fillet and best texture.

The trial involves placing 87 cod in the swim tunnel. During a 15-minute period, the velocity of the water current is increased from low to high. The fish are then removed as they became exhausted.

Need rest to be the best possible

“The objective is to get as many fish exhausted at the same time so the situation will be as similar to real trawling as possible. The exhausted cod are placed in cages submerged in a tank, where they are divided into five different groups, which recuperate for zero, two, four, six and 10 hours respectively. The first group is slaughtered immediately without any recuperation time,” says Ragnhild Aven Svalheim, Research Fellow at Nofima, who is managing the trial.

The scientists are attempting to find out the ideal recuperation time in order to optimize the muscle quality of the cod in respect to both colour and texture.

“Tests taken on trawlers show that fish which recuperate for three hours prior to slaughter have a lot of blood in their musculature. The meat becomes red and not as appetizing for the consumer. The objective of this trial is to find out how long the fish should ideally be kept in tanks prior to slaughter so that we achieve the best colour and quality of the fish - to the pleasure of the consumer and fisherman alike,” says Svalheim.

Rigor measurement for 72 hours

After all the groups of cod were slaughtered, the scientists took blood tests and a series of other tests were performed.

“The cod are then stored on ice and we measure the rigor mortis every fourth hour for 12 hours and then every eighth hour for the next 60 hours. It is important to map the onset of rigor as the fish should not be filleted while in rigor mortis. This is because the risk of fillet gaping increases and, as a result, the fillets may be downgraded. The fish is filleted after four days and is assessed by a sensory panel, which gives a score depending on the degree of redness in the meat,” says Svalheim.

The scientists at Nofima hope that this trial will enable them to find out as much as possible about the optimisation of trawl capture of white fish in order to raise the quality of the fish, both physically and visually.

Experimental tunnel

The swim tunnel, which is situated at Tromsø Aquaculture Research Station, is part of the CRISP project. The aim of the swim tunnel is to perform experiments in which individual factors may be isolated in order to simulate a situation, in for instance trawling, and improve the quality of fish captured in this way. As such, the tunnel will contribute to increased value creation and better raw materials for the consumer.

CRISP (Centre for Research-based Innovation in Sustainable fish capture and Pre-processing technology) is hosted by the Institute of Marine Research and Nofima is responsible for quality and value creation. The goals of the project are to optimise the fishery industry’s value creation and product quality.

TheFishSite News Desk © Nofima )

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