Scientists discover origins of that weird off-taste found in some onions

16 Aug 2018

Image: glebchik/Shutterstock

A culinary mystery involving onions that has plagued scientists for years has finally been solved.

Not long after we found out the complicated physics behind the snapping of spaghetti, a team of researchers based in the Czech Republic claims to have answered another kitchen mystery.

Frequent onion eaters might be familiar with the somewhat unpleasant discovery of a peculiar bitter taste found within the contents of an otherwise regular variety.

The phenomenon occurs when an onion is chopped or processed for cooking, resulting in the bitter taste.

For years, very little was known about why this particular phenomenon occurs.

Previous research suggested that onions release a compound called lachrymatory factor syntase when cut, resulting in the familiar stinging of eyes, causing someone to tear up.

Scientists concluded that several sulphur-based compounds are also formed when the onion is chopped, but none of these caused a bitter taste.

Nine new compound groups

In a paper published to the American Chemical Society’s Journal of Agricultural and Food Chemistry, the researchers described an experiment that saw them processing onions with a kitchen juicer.

While freshly obtained onion juice was normal, after 30 minutes it was found to develop a strong, bitter taste.

With this information, the team went about trying to find what exactly happens in this intervening amount of time.

To do this, the researchers performed sensory-guided high-performance liquid chromatography in order to identify the compounds that formed over time in the onion juice.

As it turned out, they discovered nine different groups of sulphur compounds in the juice, now dubbed allithiolanes.

The compounds were found to form spontaneously when an onion is damaged.

Not limited to onions, allithiolanes were also discovered in some of its relatives, such as leeks, with one of the groups found in garlic as well.

Colm Gorey was a senior journalist with Silicon Republic