Why do onions make us cry?
So who does not know that familiar feeling: tingly, stinging eyes and then the tears.
So Why would the onion, one of the key ingredient in many of our meals, cause us so much discomfort?
With plants and animals , life is about survival and reproduction and Onions are no exception. To stop predators from eating the bulbs, onions release some volatile chemicals that cause our eyes to well up.
Onions are perennial plants and in the first year of their life cycle, they form a bulb that acts as an energy store. The following year, the plant produces the flower and the seeds which will allow it to reproduce
Just recently Scientists have identified how the enzyme responsible for this process works.
The chemical at the heart of our tears is called propanethial S-oxide, which is also known as lachrymatory factor (LF). The anatomical term for our tear glands is “lacrimal glands,” and LF is the chemical that causes tears.
There are three other molecules with similar tear-inducing properties and they are all produced by plants.
Marcin Golczak, Ph.D. – an assistant professor in the Department of Pharmacology at Case Western Reserve University in Cleveland, OH – col has recently discovered the structure of the enzyme that produces LF in onions: lachrymatory factor synthase (LF synthase).
So what happens then?
When we start chopping, the cells inside the onion are broken up. When this happens an enzyme called allinase is released and this produces the chemicals that are subsequently broken down into flavor molecules. These give onions their characteristic taste.
Some of the chemicals involved in this reaction are turned into LF by LF synthase. When LF comes into contact with the front of the eye, or the cornea, nerve endings located here signal to the brain that an irritant has arrived on the scene. This, in turn, leads to signaling back from the brain to the tear glands.
Tears and blinking are subsequently initiated to remove the pesky irritant from the cornea.
The elusive enzyme
Understanding the structure and function of enzymes is a complex science. Although LF synthase was identified as early as 2002, until now, no one has been able to show how it actually works.
Harnessing health benefits
Onions have a wealth of health benefits. Studies suggest a link between the chemicals in onions and the inhibition of cancer growth, as well as improvement of sleep and mood.
As they are also a very good source of dietary vitamin C, which is a building block of collagen, onions may well play a role in hair and skin health.
Now to save us from the discomfort of tears, two groups of scientists have been working on producing tear-free onions….you read right.
One of these new onions has been shown to inhibit platelet aggregation, which is associated with cardiovascular disease.
The next time you are getting your chopping board ready to chop up an onion think the amazing biochemical processes that will unfold in front of your teary eyes.