The Scicurious Brain

The Scicurious Brain

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IgNobels 2013: The Tearless Onion


I don't know about you, but onions make me MISERABLE. I love them, and I cook with them probably 5-6 days a week, but the chopping, oh the chopping. I can barely make it halfway before I'm unable to keep my eyes open. We even have a pair of goggles we keep around to make it less miserable.

But what if there was an onion, still flavorful, and TEARLESS? Would people should "evil GMO", or would they sigh in relief? I'd be in the latter category, myself.

Well, there IS a tearless onion! It exists! But how does it taste? Well, they don't KNOW. We'll get to that.


Imai et al. "An onion enzyme that makes the eyes water" Nature, 2002.

(Observe the caption on Figure 2. You see what they did there!)

I really appreciated the authors of this paper. They (like most people who are there to be honored at the Igs) were thrilled to be at there, and a lot of fun to talk to! They were very proud of their mechanism and where the project is going. The most enthusiastic scientists are the best scientists. :)

It turns out the chemical that makes you cry from onions is actually known. It's Propanthial-s-oxide (eye watering enough just from trying to say the name!). But HOW exactly it was known was up for debate. Scientists knew that an enzyme called allinase breaks down the chemical PRENCSO to pyruvic acid. They thought that it just spontaneously went from there to the tear-jerking Propanthial-s-oxide.

The scientists on this paper thought otherwise. And they had good reason. Garlic, a cousin of onions, contains allinase. But no one ever cried over chopping garlic (unless it was from some other cause than the garlic, anyway). They added allinase specifically to PRENCSO...and got NO Propanthial-s-oxide. So the allinase alone is not responsible for the breakdown. There's another, missing enzyme.

The authors were able to isolate the tearful culprit, named lachrymatory-factor synase (Propanthial-s-oxide is often called lachrymatory factor, lachryma being latin for tears).

Further experiments showed that lachrymatory-factor synase was indeed the culprit. But if you know what the protein is, and you can find the gene for it...that means you can take it OUT. Working with collaborators in Wisconsin, the group has been able to create an onion without lachrymatory-factor synase, which produces no Propanthial-s-oxide. No lachymatroy factor? NO TEARS. The tearless onion!

The authors hypothesize that the tearless onion will actually be as or possibly MORE flavorful than the normal, tear jerking kind. This isn't because you will be free of tearful traumatizing experiences while chopping. Instead, it's because the first chemical for breakdown, PRENCSO, has an alternate pathway it can take:

(Figure 1A)

What you can see above is the chemical pathway. The LF Synase is read is your tear-jerking enzyme. If that enzyme is gone, there's another pathway, a spontaneous one, that goes to thiosulfinate, a chemical that is the FLAVOR of fresh onion...without the pain. So in theory, if you block the lachrymatory factor synthase, you can increase thiosulfinate, and end up with a tearless, yet more tasty, onion!

But is the onion more tasty? Well, here we hit a snag. We don't know. The new, tearless onion is technically not a normal onion. It's been modified. So it's not FDA approved or cleared by any other body as safe for consumption. Which means...we have a tearless onion that no one can eat. Now that will make you cry.

The views expressed are those of the author and are not necessarily those of Scientific American.

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