![Question:](images/question.gif)
Onions produce the chemical irritant known as syn-propanethial-S-oxide.
It stimulates the eyes' lachrymal glands so they release tears.
Scientists used to blame the enzyme allinase
for the instability of substances in
a cut onion. Recent studies from
Japan,
however,
proved that lachrymatory-factor synthase, (a previously undiscovered
enzyme) is the culprit (Imani et al, 2002).
The process goes as follows:
- Lachrymatory-factor synthase is released into the air when we
cut an onion.
- The synthase enzyme converts the sulfoxides (amino acids) of
the onion into sulfenic acid.
- The unstable sulfenic acid rearranges itself into syn-ropanethial-S-oxide.
- Syn-propanethial-S-oxide gets into the air and comes in contact
with our eyes. The lachrymal glands become irritated and produces
the tears!
Related
Web Sites |
- Crying
for Onion Chemistry by Megan FitzPatrick - This article from the
Chem Ecology Education Center explains why onions make you cry. It gives
suggestions on how to avoid tearing up when you cut an onion.
- National Onion Association
- This Web site provides onion information & tips, recipes, growing
areas, and industry. "The National Onion Association encourages
the United States onion industry to voluntarily exercise all reasonable
efforts to supply consumers with the highest quality, most nutritious,
and safest onions available; and furthermore, to grant appropriate
consideration and respect to the issues of food security, sound pesticide
management, and environmental stewardship."
- Onions
- This site from Texas A&M University provides all types of information
about onions such as planting tips, the varieties, the history and
laws, and onion recipes.
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Further
Reading |
- Dille,
Carolyn and Susan Belsinger. The onion book: a bounty
of culture, cultivation, and cuisine. Loveland, CO,
Interweave Press: c1996. 96 p.
- Frey,
William H. Crying: the mystery of tears. Minneapolis,
Winston Press, c1985. 175 p.
- Imani,
S. et al. Plant biochemistry: an onion enzyme that makes
the eyes water. Nature, v. 419, Oct. 17, 2002: 685.
- Parsons,
Russ. How to read a french fry and other intriguing kitchen
science. Boston, Houghton Mifflin, c2001. p 1-3.
- Rogers,
Mara Reid. Onions: a celebration of the onion through
recipes, lore, and history. Reading, MA, Addison-Wesley
Pub., c1995. 193 p.
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For
more print resources...
Search on "onion,"
"lachrymal gland" and "crying" or "tears"
in the Library of Congress Online
Catalog.
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![Photograph of person chopping onions](images/onion2.jpg)
"Share
The Meat" recipes. Ann Rosener, photographer, 1942. Prints
& Photographs Division, Library of Congress.
According to the Guiness
Book of World Records, the largest onion weighed 10 pounds 14
ounces. It was grown by V. Throup of Silsden, England.
[Mexican onion-picker
in onion field near Tracy, California]. Dorthea Lange, photographer,
[1935]. Prints & Photographs
Division, Library of Congress.
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