Question

Give reasons for tears to start flowing while cutting onions.

Answer 1

Hint: Chopping onions can cause irritation and burning sensation in the eyes. One does not have to worry because it is just a temporary sensation and its effects are not long term. There are some enzymes responsible for the tears flowing out of our eyes while dealing with onions. There are some biochemical processes responsible for this type of reaction.

Complete answer:
- Onions are responsible for the production of a chemical irritant called syn-propanethial-S-oxide. This chemical stimulates the lacrimal glands that are present in the eyes and so they release tears.
- Sequential reaction steps occur here. First of all, when we cut onions, a lachrymatory–factor synthase is released into the surrounding.
- The onions have amino acid sulfoxides present in them. So the lachrymatory factor synthase enzyme converts this amino acid sulfoxides into sulfenic acid. This sulfenic acid is unstable and rearranges itself to syn-propanethial-S-oxide.
- This syn-propanethial-S-oxide when goes into the air, comes in contact with the eyes which irritate lachrymal glands and thus tears flow down from our eyes.

Note: Cutting onions can be a hard task if we have to deal with tears. However, there are some ways by which you could avoid them. When sharp knives are used, there will be less damage to the cell walls and less irritants will be released in the surrounding air. Another trick is that, before cutting onions, if they are chilled enough then less propanethial S-oxide would evaporate. One would get some relief by it. The exposed parts of the onions should be put away from you as much as possible while working in the kitchen.