onion

Onion
Onions
Scientific classification
Kingdom: Plantae (unranked): Angiosperms (unranked): Monocots Order: Asparagales Family: Alliaceae Genus: Allium Species: A. cepa
Binomial name
Allium cepa L.

Onion is a term used for many plants in the genus Allium. They are known by the common name "onion" but, used without qualifiers, it usually refers to Allium cepa. Allium cepa is also known as the "garden onion" or "bulb" onion. It is grown underground by the plant as a vertical shoot that is used for food storage, leading to the possibility of confusion with a tuber, which it is not.

Allium cepa is known only in cultivation,^[1] but related wild species occur in Central Asia. The most closely-related species include Allium vavilovii Popov & Vved. and Allium asarense R.M. Fritsch & Matin from Iran.^[2] However Zohary and Hopf warn that "there are doubts whether the vavilovii collections tested represent genuine wild material or only feral derivatives of the crop."^[3]

Uses

Onions, one of the oldest vegetables known to humankind, are found in a large number of recipes and preparations spanning almost the totality of the world's cultures. They are nowadays available in fresh, frozen, canned, pickled, powdered, chopped, and dehydrated forms. Onions can be used, usually chopped or sliced, in almost every type of food including cooked foods and fresh salads and as a spicy garnish. They are rarely eaten on their own but usually act as accompaniment to the main course. Depending on the variety, an onion can be sharp, spicy, tangy and pungent or mild and sweet.

Onions pickled in vinegar are eaten as a snack. These are often served as a side serving in fish and chip shops throughout the United Kingdom and are referred to simply as "Pickled Onions". Onions are widely-used in India / Pakistan and are fundamental in the local cuisine. They are commonly used as a base for curries or made into a paste and eaten as a main course or as a side dish. Onion is called "Pyaaz" in Urdu,(प्याज़)in Hindi, "Erulli/Ulla gaddi" in Kannada "ulli paya" (ఉల్లిపాయ) or "Erra gadda" (ఎర్ర గడ్డ) in Telugu "Sawala" or "Ulli" in Malayalam and "Kanda" in Marathi.

Tissue from onions is frequently used in science education to demonstrate microscope usage, because they have particularly large cells which are readily observed even at low magnifications.^[4]

Historical uses

It is thought that bulbs from the onion family have been used as a food source for millennia. In Bronze Age settlements, traces of onion remains were found alongside fig and date stones dating back to 5000 BC.^[5]

However, it is not clear if these were cultivated onions. Archaeological and literary evidence such as the Book of Numbers 11:5 suggests cultivation probably took place around two thousand years later in ancient Egypt, at the same time that leeks and garlic were cultivated. Workers who built the Egyptian pyramids may have been fed radishes and onions.^[5]

The onion is easily propagated, transported and stored. The Ancient Egyptians worshipped it,^[6] believing that its spherical shape and concentric rings symbolized eternal life. Onions were even used in Egyptian burials as evidenced by onion traces being found in the eye sockets of Ramesses IV. They believed^{[citation needed]} that, if buried with the dead, the strong scent of onions would bring breath back to the dead.

In ancient Greece, athletes ate large quantities of onion because it was believed that it would lighten the balance of blood. Roman gladiators were rubbed down with onion to firm up their muscles. In the Middle Ages onions were such an important food that people would pay their rent with onions and even give them as gifts.^[6] Doctors were known to prescribe onions to facilitate bowel movements and erection, and also to relieve headaches, coughs, snakebite and hair loss. The onion was introduced to North America by Christopher Columbus on his 1492 expedition to Hispaniola. Onions were also prescribed by doctors in the early 1500s to help with infertility in women, and even dogs and cattle and many other household pets. However, recent evidence has shown that dogs, cats, and other animals should not be given onions in any form, due to toxicity during digestion.^[7]

Medicinal properties and health effects

Wide-ranging claims have been made for the effectiveness of onions against conditions ranging from the common cold to heart disease, diabetes, osteoporosis, and other diseases.^[8] They contain chemical compounds believed to have anti-inflammatory, anticholesterol, anticancer, and antioxidant properties such as quercetin. However, it has not been conclusively demonstrated that increased consumption of onions is directly linked to health benefits. Some studies have shown that increased consumption of onions reduces the risk of head and neck cancers.^[9] In India some sects do not eat onion due to its alleged aphrodisiac properties.

In many parts of the world, onions are used to heal blisters and boils. A traditional Maltese remedy for sea urchin wounds is to tie half a baked onion to the afflicted area overnight. In the morning, the spikes will be in the onion.^{[citation needed]} In the United States, products that contain onion extract are used in the treatment of topical scars; some studies have found their action to be ineffective,^[10][11][12] while others found that they may act as an anti-inflammatory or bacteriostatic^[13] and can improve collagen organization in rabbits.^[14]

Onions may be especially beneficial for women,^[15] who are at increased risk for osteoporosis as they go through menopause, by destroying osteoclasts so that they do not break down bone.

An American chemist has stated^[16] that the pleiomeric chemicals in onions have the potential to alleviate or prevent sore throat.

Shallots have the most phenols, six times the amount found in Vidalia onion, the variety with the lowest phenolic content. Shallots also have the most antioxidant activity, followed by Western Yellow, pungent yellow (New York Bold^[17]), Northern Red, Mexico, Empire Sweet, Western White, Peruvian Sweet, Texas 1015, Imperial Valley Sweet, and Vidalia. Western Yellow onions have the most flavonoids, eleven times the amount found in Western White, the variety with the lowest flavonoid content.

For all varieties of onions, the more phenols and flavonoids they contain, the more antioxidant and anti-cancer activity they provide. When tested against liver and colon cancer cells, Western Yellow, pungent yellow (New York Bold^[17]) and shallots were most effective in inhibiting their growth. The milder-tasting varieties—Western White, Peruvian Sweet, Empire Sweet, Mexico, Texas 1015, Imperial Valley Sweet, and Vidalia—showed little cancer-fighting ability.^[17]

Shallots and ten other onion (Allium cepa L.) varieties commonly available in the United States were evaluated: Western Yellow, Northern Red, pungent yellow (New York Bold™), Western White, Peruvian Sweet, Empire Sweet, Mexico, Texas 1015, Imperial Valley Sweet, and Vidalia. In general, the most pungent onions delivered many times the benefits of their milder cousins.^[17]

Some species of onion are poisonous. The wild onion Allium canadense has many look alikes and if misidentified symptoms include anemia, Heinz bodies and death.^[18]

Onions and eye irritation

As onions are sliced or eaten, cells are broken, allowing enzymes called alliinases to break down amino acid sulphoxides and generate sulphenic acids. Sulphenic acids are unstable and spontaneously rearrange into a volatile gas called syn-propanethial-S-oxide. The gas diffuses through the air and eventually reaches the eye, where it binds to sensory neurons, creating a stinging sensation. Tear glands produce tears to dilute and flush out the irritant.^[19]

Supplying ample water to the reaction while peeling onions prevents the gas from reaching the eyes. Eye irritation can, therefore, be avoided by cutting onions under running water or submerged in a basin of water. Rinsing the onion and leaving it wet while chopping may also be effective. Another way to avoid irritation is by not cutting off the root of the onion, or by doing it last, as the root of the onion has a higher concentration of enzymes.^[20] Using a sharp blade to chop onions will limit the cell damage and the release of enzymes that drive the irritation response. Chilling or freezing onions prevents the enzymes from activating, limiting the amount of gas generated. Eye irritation may be avoided by having a fan blow the gas away from the eyes as the onion is being cut. The volume of sulfenic acids released, and the irritation effect, differs among Allium species.

It is also possible to avoid eye irritation by wearing goggles or any eye protection that creates a seal around the eye. Contact lens wearers can experience less immediate irritation as a result of the slight protection afforded by the lenses themselves. It may also be that lens wearers are familiar with controlling the more reflexive actions of their eyes with regards to irritation; as this is an ability they require when manipulating the lenses to prevent blinking.

On January 31, 2008, the New Zealand Crop and Food institute created a strain of "no tears" onions by using gene-silencing biotechnology.^[21]

Propagation

Onion and shallot output in 2005

Onion growing shoots

Onions may be grown from seed or, more commonly today, from sets started from seed the previous year. Onion sets are produced by sowing seed very thickly one year, resulting in stunted plants which produce very small bulbs. These bulbs are very easy to set out and grow into mature bulbs the following year, but they have the reputation of producing a less durable bulb than onions grown directly from seed and thinned.

Seed-bearing onions are day-length sensitive; their bulbs begin growing only after the number of daylight hours has surpassed some minimal quantity. Most traditional European onions are what is referred to as "long-day" onions, producing bulbs only after 15+ hours of daylight occur. Southern European and North African varieties are often known as "intermediate day" types, requiring only 12–13 hours of daylight to stimulate bulb formation. Finally, "short-day" onions, which have been developed in more recent times, are planted in mild-winter areas in the fall and form bulbs in the early spring, and require only 9–10 hours of sunlight to stimulate bulb formation.

Either planting method may be used to produce spring onions or green onions, which are the leaves and/or immature plants. Green onion is a name also used to refer to another species, Allium fistulosum, the Welsh onion, which is said not to produce dry bulbs.

The Tree onion produces bulbs instead of flowers and seeds, which can be planted directly in the ground.

Varieties

Brown and white onions

Yellow onions

Flower head of a yellow onion

Red onions

• Bulb onion – Grown from seed (or onion sets), bulb onions range from the pungent varieties used for dried soups and onion powder to the mild and hearty sweet onions, such as the Vidalia from Georgia or Walla Walla from Washington that can be sliced and eaten on a sandwich instead of meat.
• Multiplier onions – May refer to perennial green onions, or to onions raised from bulbs which produce multiple shoots, each of which forms a bulb. The second type is often referred to as a Potato onion.
• Tree onion or Egyptian onion - Produce bulblets in the flower head; a hybrid of Allium cepas.
• Welsh onion – Sometimes referred to as green onion or spring onion, although these onions may refer to any green onion stalk.
• Leek

Production trends

Onion field during harvest, Vale, Oregon (USA).

Top Ten Onions Producers — 2005 (1000 tonnes)
China	9,793
India	5,500
United States	3,346
Turkey	2,220
Pakistan	1,764
Russia	1,758
South Korea	1,750
Japan	1,637
Egypt	1,302
Spain	1,149
World Total	64,101
Source: UN Food & Agriculture Organisation (FAO)[1]

The Onion Futures Act, passed in 1958, bans the trading of futures contracts on onions in the United States, after farmers complained about alleged market manipulation at the Chicago Mercantile Exchange. It provides economists with a unique case study in the effects of futures trading on agricultural prices. It remains in effect as of 2008.

Aroma attributes

• 3-Mercapto-2-methylpentan-1-ol ^{[22], [23]}

Potential medicinal use

3-mercapto-2-methylpentan-1-ol in onion was found to have an antioxidant potent which inhibites peroxynitrite induced diseases ^[24].

Onions in language

Lists of miscellaneous information should be avoided. Please relocate any relevant information into appropriate sections or articles. (April 2009)

• Onions find mention in William Shakespeare's tragedy Antony and Cleopatra IV.ii, in which the character Enobarbus, observing Antony's farewells to some of his servants, declares: "What mean you, sir,/To give them this discomfort? Look, they weep;/And I, an ass, am onion-eyed: for shame,/Transform us not to women."
• In French, the expression "Ce n'est pas tes oignons" (literally: "It's not your onions") means that a topic is none of the listener's business.
• Expressions referring to "layers of the onion" evoke the process of peeling back the layers of something (a person, reality, etc.), without however reaching a core - the centre of the onion being simply another layer. The metaphor is thus used to challenge the notion that there is a core/essence "underneath" surface layers, stressing the continuity between layer and core. Due to the number of layers in an onion it can also be used simply to evoke complexity; something having "many layers," or "always another layer behind this one."
• The Onion is an American "fake news" organization.

Pictures

Red onion	Onion fields near Elba, New York	Onions cooked in a frying pan	Onion weighing and packing in The Netherlands
Dried onion	Spring onion

Notes

References

• Sen, Colleen T. (2004). Food culture in India. Greenwood Publishing. ISBN 0313324875.
• Barbagallo, Tricia (June 01, 2005). "Black Beach: The Mucklands of Canastota, New York" (PDF). http://www.archives.nysed.gov/apt/magazine/MagSummer05FeatureArticle_000.pdf. Retrieved on 2008-06-04. 
• A comic song has been recorded by UK comedy pop group The Badger Famine based entirely on this site's 'Historical Uses' paragraph. Lyrics can be found here: http://www.thebadgerfamine.co.uk/finestbulb.html

See also

• Allistatin
• Onion Johnny
• Herbalism
• List of Allium species
• The Onion American "fake news" organization.
• Welsh onion

External links

Look up onion in Wiktionary, the free dictionary.

• PROTAbase on Allium cepa
• How to safely cut an onion (by Rachael Ray)
• Watch the Video: No Cry Onion Chopping (with Jonathon Stewart)
• Medicinal Pungent Onions