New research reveals the taste of fish

Food technology Food quality

Geosmin and 2-methylisoborneol occur naturally in lakes and watercourses, but excessive concentrations of these two substances can give fish a "muddy" taste. Researchers at the National Food Institute, Technical University of Denmark, have now developed sensory profiles that can predict problems with taste in aquaculture fish and thus make it possible to eliminate such problems entirely.

The sensory panel at the National Food Institute have tasted their way through numerous rainbow trout with various concentrations of geosmin and 2-methylisoborneol. The purpose of the project was to develop sensory profiles of the taste and smell of the fish to make it possible to predict taste problems in aquaculture fish, with especial emphasis on off-taste and off-smell. The National Food Institute was responsible for the development of the sensory profiles, while the Faculty of Science, University of Copenhagen, handled the chemical analyses for the two substances.

Harmless, but taste bad

Geosmin and 2-methylisoborneol are substances that occur naturally in lakes and watercourses. They are harmless to people and animals in their usual concentrations. However, the problem is that these two substances can cause the fish to taste "muddy" and "mouldy", respectively. Most people report that geosmin leaves a "burning muddy" taste in the mouth, although some people cannot taste the substance at all.  

Predict the taste and smell of the fish

For aquaculture and fish farmers, it is essential that the fish both smell and taste good, otherwise consumers will not want to buy them. Aquaculture fish must be without feeding when they are kept in the ponds that are known as "depuration ponds" prior to slaughtering. If they contain excessive concentrations of geosmin, for example, the substance will generally be diluted in the clean water of the depuration pond. Excessive concentrations of geosmin and 2-methylisoborneol can, however, be eliminated even before the fish are released into depuration ponds.  

Using sensory analyses, the National Food Institute has evaluated the off-taste of the fish at different concentrations of the substances and has subsequently prepared sensory profiles of the relationship between the levels of the substances and the smell and taste of the fish. In collaboration with the Faculty of Science, University of Copenhagen, researchers at the National Food Institute mapped out the scope of the problem, so that it is now possible to perform analyses of the water to measure the levels of the substances and thus predict problems with the taste of the fish. It is therefore now possible at an early stage – i.e. while the fish are still in the production pond – to take steps to prevent the development of geosmin and 2-methylisoborneol.

The results obtained by the researchers do not apply exclusively to rainbow trout; they can also be extrapolated to other species of fish farmed in fresh water. The working relationship and the results from the fish farm project have opened the door to organising aquaculture fish production in which taste problems of this type can be completely eliminated.

Read more

Read more in the journal Aquaculture Research: Evaluation of geosmin and 2-methylisoborneol off-flavour in smoked rainbow trout fillets using instrumental and sensory analyses.  

The project was financed through a grant from the Danish AgriFish Agency.