The Why Series
It happens to me all the time. A minute ago I would be happily chopping veggies for dinner and the next minute you would find me crying copious tears. People around me would look at me with sympathetic eyes but would talk to me from a safe distance. Why? No! The problem is not me. It’s the onions!
Let us find out the answer:-
The answer to this question can be found in the amazing word of biochemistry.
This is due to the presence of few chemicals in onions. Onions are packed with sulphur. They also contain an enzyme (it is a biological catalyst and is almost always a protein) called alliinase. When we cut an onion the enzyme alliinase reacts with amino acid sulfoxide to produce 1-propenesulfenic acid. Sulfenic acid is highly unstable and is quickly rearranged by another enzyme called synthase to form a new compound called syn-propanethial S-oxide.
This new compound syn-propanethial S- oxide is volatile (substance vaporizing fast) in nature. It vaporises and meets our eyeballs where it reacts with the moisture in our eyes and produces sulphuric acid. Production of this gas peaks 30 seconds after mechanical damage to onion which stimulates our sensory neurons to cause burning and itching sensation in our eyes. To prevent our eyes from burning our tear glands produce tears and we are left with watery eyes. This is the reason for crying while cutting onions.
I have an interesting tip for you to get rid of watery eyes while cutting onions. Keep the onions in the fridge and let it get cold for about 10 minutes and then cut, it becomes less reactive and doesn’t cause burning or itching in our eyes.