Why do you cry when you cut onions?

En trogen resekamrat under den 24h-resan till Japan blev Why do men have nipples? av Mark Leyner och Billy Goldberg. Den ena är läkare, den andra är författare och i boken hittar vi en rad intressanta frågor och svar. Bortsett från frågor som "Is it more sanitary to be spit or peed on?" och "What causes an ice-cream headache?" hittar vi "Why do you cry when you cut onions?".

Cutting an onion releases an enzyme called lachrymatory-factor synthase. This starts the process that leads to tears. This enzyme then reacts with amino acids in the onion and the amino acids are converted to sulfenic acids. The sulfenic acids spontaneously rearrange to form syn-propanethial-S-oxide, which is released into the air. When this checmical reaches the eyes, it triggers the tears by contacting nerve fibers on the cornea that activate the tear glands. Now you are crying.

Scientists have tried to make a "non-crying" onion but it seems that the crying enzymes are also responsible for the zesty onion flavor. But there may be some hope on the way. The group of Japanese plant biochemists that only recently discovered lachrymathory-factor synthase, the crying enzyme, believe that "it might be possible to develop a non-lachrymatory onion by suppresing the lachrymatory-factor-synthase gene while increasing the yield of thiosulfphinate." Sounds delicious!

In the meantime there are several solutions to try to avoid the problem of the onion-induced tears. Heating onions before chopping, cutting under a steady stream of water, or wearing googles. The most reliable: ordering takeout.

Sid. 8-9, Why do men have nipples (Mark Leyner & Billy Goldberg)

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