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Scientific American Instant Egghead
Start chopping a pungent onion
and before too long you're bound to tear up.
How exactly does this bulbous veggie have the power to make us cry?
The second you slice into an onion you change its chemistry.
Cutting an onion ruptures its cell walls.
You can think of these walls as sturdy balloons
that hold in a cells contents.
When a knife breaks through, [pop]
swarms of molecules and enzymes escape.
Some of those enzymes break down sulfur compounds present in the onion
generating sulfenic acids in the process.
Other chemical reactions convert sulfenic acids
into a volatile and irritating gas called onion lachrymatory factor.
When this gas wafts into your eyes,
certain neurons instruct your tear ducts to flush out this potentially harmful substance.
Fortunately, there are a few tricks you can use to keep the waterworks to a minimum.
Storing the onion in the fridge or freezer for at least 30 minutes before chopping,
slows down its enzymes which should help prevent tears.
Briefly boiling an onion should have the same effect.
High heat can deactivate enzymes.
Another strategy is cutting the onion under running water
to prevent the gas from reaching your eyes.
But the easiest solution is probably a pair of ski goggles or sunglasses.
Hmm
[chop, chop]
Umm, if goggles or glasses don't work out so well, don't worry.
Scientists are trying to tackle the problem too.
Researchers in Japan and New Zealand have collaborated to create a tear free onion.
They silenced one of the genes that makes onion lachrymatory factor, the volatile gas that irritates your eyes.
But don't look for it on the shelf, this genetically modified product is not currently on the market.
Other researchers used traditional plant breeding to create the "Ever Mild", a yellow onion with really low levels of the volatile gas.
You can find it in some grocery stores.
But until these products are more widely available, we'll probably have to stick with Kleenex and sunglasses.
For Scientific American's Instant Egghead, I'm Ferris Jabr.
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【生物小常識】洋蔥到底怎麼把我們惹哭的? (Why Do Onions Make Us Cry? - Instant Egghead #62)

13403 分類 收藏
羅紹桀 發佈於 2015 年 9 月 13 日
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