Dr Gabriel Uguru
LET’S relax a bit and take a lighthearted look at the humble onions. Sorry, I am not going to describe onions for you or how they are grown, or for that matter, I am not going to tell you that onions belong to the Allium genus like garlic, leek, chives, etc…. I assume you already know about all those things. This article is designed for light-reading and enjoyment, nothing heavy, ok.
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Your eyes always water when you are peeling onions; but do you know why? Onions contain sulphur and when you peel an onion the sulphur is released, which on contact with atmospheric oxygen forms sulphur dioxide, SO2 (Sulfur is the recommended IUPAC spelling but Sulphur is preferred for use in the Queen’s English). It is this sulphur dioxide that makes your eyes to water! It is a colourless gas with a pungent or sharp chocking odour.
However in-depth analyses by scientists have shown that the actual tear-inducing culprit when onions are cut is a chemical called propanethial S-oxide, simply called the lachrymatory factor (LF). When you start chopping onions, several chemicals are released of which LF and an enzyme called allinase are amongst them. Allinase catalyses (i.e. builds) some of the chemicals contained in onions, which are later broken down into molecules to give onions their distinctive flavours.
We do have sulphur monoxide (SO) as well besides sulphur dioxide, but it is an inorganic compound, so disregard it. And it gets even more interesting; when your eyes water, the water molecule, H2O, reacts with SO2 to give you, …. wait for it, wait for it, …. sulphurous acid, H2SO3, which is a step away from sulphuric acid, in fact it is an intermediate step in the formation of acid rain from sulphur dioxide! You can heave a sigh of relief because it is difficult to detect sulphurous acid in solution except only in gas phase. But let’s assume that H2SO3 is there, it combines with the salt, NaCl, from your tears to make hydrochloric acid, thus:
H2SO3 + NaCl = HCl + Na2SO3.
Tut, tut, remember your secondary school Chemistry and balance the equation! Failure to do so would incur a kick up your behind from your Chemistry teacher! Thus:
H2SO3 + 2NaCl = 2HCl + Na2SO3.
I take it by now the tears are really gushing from your eyes, what with these “difficult” chemistries you have been subjected to, which means that more water from your tears might even react with sodium sulphite (Na2SO3) to form another acid, sulphuric acid! Those are loads of acids you are making, guys! 😂😂😂
Courage, my friends, courage. If it is of any consolation, many varieties of onions with low or virtually non-tear-inducing LF (lachrymatory factor) have been created by scientists. These were done by simply mutating or deleting the LF so that its an expression (i.e. effect) was either diminished or entirely removed. But the jury is still out there on whether the mutants still retain all the good qualities of onions or for that matter, the acceptability of such mutants by the wider public.
There are several advises on how to reduce the stinging to the eyes when cutting onions. These range from freezing onions for 30 minutes prior to cutting to slicing onions in two and soaking them in water before cutting. But I am unable to give you a definite recommendation as the science behind all these homespun methods have not been proven. But my late Grandma used to swear by them – and the double entendre here is that she did know her onions! 😂😂😂
But ask yourself, all these aggro and shedding of tears before you can eat onions; are they worth it? The answer is Yes and No, depending on individual viewpoints.
Onions do have both culinary and health benefits otherwise they wouldn’t be as popular as they are. As onions are rich in organic sulphur compounds, eating onions may help reduce the level of cholesterol in your body. It’s been suggested that onions have a reducing effect on colorectal cancer by inhibiting the frequency of cell mutation and tumour growth. But the mechanism of the process is not yet proven – so, please take this information with a pinch of salt! Pinch of salt, that’s a good one 😂😂😂. Catch the joke? No? A combination of onions and salts theoretically gives you acid – revise (study) the above chemistry! But joking aside, definitely, onions contain antioxidants important in reducing the formation of free radicals that contribute to ageing and cancer, amongst other things. Onions are also sources of vitamins and minerals however, they could cause allergies in some people.
Sulphur dioxide can induce asthma in some individuals but not to worry, some of the sulphurs in onions are actually good for alleviating asthma. But that does not mean that you should stuff yourself with onions or your breath will stink!
