The Science of Aroma: When Fish Smells ‘Fishy’

Everyone has experienced the smell of fish, as well as the smell when fish has gone bad. A researcher in Germany is studying why fish sometimes smells ‘fishy’ and why customers often smell other aromas (not just a fish smell) when they buy fish.

Mohamed Mahmoud, doctoral candidate at the Department of Chemistry and Pharmacy at FAU, has identified various off-flavours in fish raised in aquaculture as part of his doctoral thesis. His goal is to discover how to reduce unpleasant musty notes in the taste of fish.

Eating fish as part of a high-protein diet is healthy, which is why more and more people have put salmon and other types of fish on the menu. However, this trend also means that as the demand for wild-caught fish has increased and why natural resources are gradually being depleted. As a result, the ecological balance is disturbed, threatening long-term food security around the world.

“This is why aquacultures where fish are raised are important,” explained Prof. Dr. Andrea Büttner from the Chair of Food Chemistry at FAU’s Emil Fischer Centre.

However, there is one clear disadvantage to farm-raised fish from the consumers’ perspective: the fish often carry undesirable flavours. These can come from micro-organisms in the aquaculture ponds, or other substances entering the water and creating strong aromas which are then present in the fish. The musty, earthy smell, for example, is typically caused by two substances: geosmin, and the chemical compound 2-methylisoborneol (MIB), which has a rotten fish smell. It was previously assumed that these substances were primarily responsible for off-flavours in fish. It was unclear whether other culprits might be responsible for off smells in fish.

Mohamed Mahmoud’s experiments went looking for other answers. In addition to geosmin and MIB, he identified ten other substances with a musty-earthy smell, including one that smells like manure.

“The manure smell most likely comes from livestock husbandry, such as pig farms, but other substances appear to be the result of odour-producing disintegration of pesticides. These substances run off over land into the water and get into the fish,” said Mahmoud.

This made it clear that the conventional wisdom on this matter needs to be looked at more critically and that the sources of flavour problems are significantly more complex than previously assumed. Mahmoud’s main goal is to discover ways to avoid off-flavours in farm-raised fish, as aquaculture is certain to play an even bigger role in future.

The work has also showed just how complex the combinations of various aromas typical for fish are. The young researcher has identified aromas in fish that smell like, for example, geraniums, citrus, eucalyptus, caramel, peach or black pepper.

“It isn’t unusual; food aromas are generally very complex and it’s difficult to identify the individual components of an overall aroma – unless you use our targeted analytics which allow you to individually identify aromatic substances,”

explained Mahmoud.

“Our main goal is still to find, among all the possible substances, exactly those substances that are perceived negatively and that aren’t typical for fish – especially in comparison with wild-caught fish.”

Photo credit: http://www.colourbox.com. Material used in the preparation of this article has been drawn from idw – Informationsdienst Wissenschaft.

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