Mark Antony in Shakespeare’s Cleopatra could have referred to “the tears that reside within the onion”. However why do onions truly make us cry? And why do just some onions make us blub on this means when others, together with associated “allium” crops corresponding to garlic, barely ever draw a tear when chopped?
When any vegetable is broken, its cells are ripped open. The plant usually then tries to defend itself by releasing bitter-tasting chemical compounds known as polyphenols that may be off-putting to hungry animals attempting to eat it. However an onion’s defence mechanism goes additional, producing an much more irritating chemical, propanthial s-oxide, meant to cease the plant being consumed by pests.
This risky chemical is what’s generally known as a lachrymatory issue. Its volatility implies that, as soon as it’s launched, it rapidly evaporates and finds its means into our eyes. There it dissolves within the water overlaying the floor of our eyes to kind sulphenic acid. This irritates the lacrimal gland often known as the tear gland, therefore the relatively grand title of lachrymatory issue. As a result of the quantity of acid produced is so small, its impact is barely irritating and never dangerous.
The discharge of propanthial s-oxide was initially regarded as down to at least one enzyme within the onion generally known as allicinase, a organic catalyst that accelerates the manufacturing of the eye-irritating compound. However some analysis has steered two enzymes may very well be wanted to produces these eye-watering results.
This extra complicated clarification begins with the sulphur the onion absorbs from the bottom and holds in a compound known as PRENCSO 1 (1-propenyl-L-cysteine sulphoxide). When the onion is broken it releases the allicinase, which reacts with the PRENCSO to supply ammonia and one other chemical known as 1-propenylsulphenic acid. The second enzyme, generally known as a lachrymatory-factor synthase, then turns this into the troublesome propanthial s-oxide.
Shutterstock
So why do some onions have extra of an eye-stinging impact than others? There may be numerous debate about this. One believable clarification is that it’s associated to the quantity of sulphur the onion has absorbed from the bottom, which may rely upon the soil and the rising circumstances. Greater ranges of sulphur within the soil assist enhance each the yield and pungency of onions.
Actually sweeter onions are inclined to have much less of the sulphur-containing compounds that finally produce the propanthial s-oxide. Nevertheless it’s additionally attainable that no two onions from the identical bag could have the identical impact, so reducing into the vegetable would be the solely approach to know if it is going to make you cry.
Nevertheless, we’ve got a greater concept why onion’s cousin garlic doesn’t have the identical impact. It incorporates a barely totally different compound known as alliin or PRENCSO 2, which doesn’t breakdown additional into eye-stinging chemical compounds. As an alternative it produces allicin, which has been linked to lots of garlic’s well being advantages.
Cease the tears
One resolution to the crying downside could also be to re-engineer the standard onion by selective breeding or genetic modification to suppress the lachrymatory-factor synthase enzyme. This may additionally have the additional advantage of enhancing how onions style as much less propanthial S-oxide would imply extra thiosulphinate, the compound related to the flavour of recent onions.
There are additionally a variety of lower-tech options which have been steered to resolve the onion-chopping downside. Because the response includes enzymes, the speed of response and quantity of irritating chemical compounds produced could be lower by both damaging the enzymes or slowing them down.
Shutterstock
In principle, blanching the onions (scalding them with boiling water then plunging them into freezing chilly water) will denature the enzymes concerned and so stop the response from occurring. This technique is used when freezing many greens but it surely is probably not sensible to boil your onions earlier than chopping them.
Slowing the response could be achieved by by placing your onions within the fridge or freezer earlier than chopping. Nevertheless it’s finest to not retailer onions in a fridge in the long run as they develop into soggy and gentle and lose their flavour, in addition to making an disagreeable odor. It’s best to maintain your onions in a cool darkish place with air move that isn’t as humid because the fridge.
Different approaches contain drawing the risky chemical compounds away from you as you might be chopping the onion. This may very well be accomplished by utilizing a cooker hood or working water, stopping the compounds making their approach to your eyes. You’ll be able to even purchase goggles to cease the irritant reaching your eyes. However the capability of evaporated propanthial s-oxide to succeed in our eyes regardless implies that even then try to be ready to weep as you slice.
