'No More Tears' Onions? It May Be Possible
Excerpt By Alison McCook, Reuter's Health

NEW YORK (Reuters Health) - Researchers from Japan have discovered that the tear-inducing substance in onions is produced by a compound that, contrary to previous expectations, has nothing to do with the onion's flavor.

This finding suggests that it may one day be possible to genetically engineer an onion that does not make cooks cry, and tastes just as good as the original, the authors write in the October 17 issue of Nature.

Previous research has suggested that the eye-burning substance squirted from chopped onions, propanthial S-oxide or lachrymatory factor, was produced by a substance called alliinase, as a result of the chemical pathway that leads to the onion's flavor.

In an E-mail interview with Reuters Health, the researchers, led by Dr. Shinsuke Imai of the House Foods Corporation in Chiba, Japan, said that the role propanthial S-oxide plays in the onion remains unclear.

"It may be possible that onions acquired the ability to produce propanthial S-oxide as a kind of defense mechanism," they said.

In the most recent discovery, Imai and colleagues found that lachrymatory factor actually results from a reaction involving a previously unknown substance, aptly titled lachrymatory-factor synthase, which plays no role in the onion's distinctive taste.

"It may be possible to develop a non-lachrymatory onion that still retains its characteristic flavor and high nutritional value by downregulating the activity of this synthase enzyme," Imai and colleagues write.

The authors told Reuters Health that they are currently working on developing a so-called "tear-free" onion, but noted it would likely be years before it appears on market shelves.

"It is not certain that a 'tear-free' is fully accepted by consumers, although I personally hope that it will gain some consumer preference over regular onions," Imai said on behalf of all the researchers.

SOURCE: Nature 2002;419:685.

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