Why does seafood smell fishy?

The most familiar smell of sea food is the smell emanating from some seafood. The essence of this flavor is trimethylamine. Trimethylamine is a toxic gas that exhibits a strong fishy smell at low concentrations, and an ammonia-like smell at high concentrations, such as - fart! Is it similar to indole?

Trimethylamine oxide tastes sweet and fresh, and it also contributes to the deliciousness of seafood. More importantly, it is an important means for marine organisms to survive in seawater. Does this sound a bit strange?

We all know that the salt content of one kilogram of seawater is about 35 grams, or about 3%, while the dissolved mineral content in the cells of most marine organisms is less than 1%, which means that seawater The osmotic pressure is much higher than that of most marine organisms. With such a large osmotic pressure difference, water in biological cells will be precipitated. If there are no special life-saving measures, marine organisms will become dried fish in the sea before they enter our mouths.

Trimethylamine oxide is a life-saving weapon for these marine creatures.

For some terrestrial organisms, trimethylamine oxide is just a passer-by, such as us humans. After passing through the kidneys, it is excreted in the urine. However, in most marine organisms, due to the impermeability of gills and reabsorption by small urethra, trimethylamine oxide is preserved in the body and becomes an important organic penetrant and protein stabilizer. By changing the permeability of the cell membrane and filling the cells, the osmotic pressure of the fish body is adjusted to prevent the fish body from being sucked dry by sea water.

Some marine organisms with relatively high levels of trimethylamine oxide, such as sharks, have trimethylamine oxide in their bodies that can account for 7% of the dry matter weight of their tissues.

After the fish dies, under the action of microorganisms, especially anaerobic bacteria, the oxidized trimethylamine will be reduced to trimethylamine, the culprit of the fishy smell. This is why fresh fish are very sweet, while fish that have been dead for a while will emit a strong fishy smell.