Many plants in the genus Allium 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 and 'shallot'.
Origin and distribution
Allium cepa is known only in cultivation, 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.[1] 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."[2]
Uses
Onions are used in
salsa.
Onions are available in fresh, frozen, canned, pickled, 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, 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. Onions are a staple food in
India, and are therefore fundamental to Indian cooking.
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.
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.[citation needed]
Onions have been used to clear the smell of paint from newly decorated rooms.
Historical uses
It is thought that bulbs from the onion family have been used as a food source for millennia. In Caananite Bronze Age settlements, traces of onion remains were found alongside fig and
date stones dating back to 5000 BC.[citation needed] However, it is not clear if these
were cultivated onions. Archaeological and literary evidence 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.[3]
The onion is easily propagated, transported and stored. Egyptians worshipped it, 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 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 for their rent with onions and even give them as gifts.[citation needed] Doctors were known to prescribe onions to relieve headaches,
snakebite and hair loss. The onion was introduced to North
America by Christopher Columbus on his 1492 expedition to Haiti. 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.
Medicinal properties and health benefits
Evidence suggests that onions may be effective against the common cold, heart disease, diabetes, osteoporosis, and other diseases. They contain
anti-inflammatory, anticholesterol, anticancer, and antioxidant components such as quercetin.[4]
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 (such as Mederma) are
used in the treatment of topical scars.[citation needed]
In homeopathy, Allium cepa is used for rhinorrhea and hay fever.[5]
Onions, like garlic, are members of the Allium family, and
both are rich in powerful sulfur-containing compounds that are responsible for their pungent odors and for many of their
health-promoting effects. Onions contain allyl propyl disulphide, while garlic is rich in allicin, diallyl disulphide, diallyl
trisulfide and others. In addition, onions are very rich in chromium, a trace mineral that helps cells respond to insulin, plus
vitamin C, and numerous flavonoids, most notably, quercetin.
The higher the intake of onion, the lower the level of glucose found during oral or intravenous glucose tolerance tests.
Experimental and clinical evidence suggests that allyl propyl disulfide is responsible for this effect and lowers blood sugar
levels by increasing the amount of free insulin available. Allyl propyl disulfide does this by competing with insulin, which is
also a disulphide, to occupy the sites in the liver where insulin is inactivated. This results is an increase in the amount of
insulin available to usher glucose into cells causing a lowering of blood sugar.
In addition, onions are a very good source of chromium, the mineral component in glucose
tolerance factor, a molecule that helps cells respond appropriately to insulin. Clinical studies of diabetics have shown that
chromium can decrease fasting blood glucose levels, improve glucose tolerance, lower insulin levels, and decrease total
cholesterol and triglyceride levels, while increasing
HDL-cholesterol levels. Marginal chromium deficiency is common in the United
States, not surprising since chromium levels are depleted by the consumption of refined sugars and white flour products as well
as the lack of exercise. One cup of raw onion contains over 20% of the Daily Value for this important trace mineral.
The regular consumption of onions has, like garlic, been shown to lower high cholesterol levels and high blood pressure, both
of which help prevent atherosclerosis and diabetic heart disease, and reduce the risk of heart attack or stroke. These beneficial
effects are likely due to onions' sulfur compounds, its chromium and its vitamin B6, which helps prevent heart disease by
lowering high homocysteine levels, another significant risk factor for heart attack and stroke. Onions have been singled out as
one of the small number of vegetables and fruits that contributed to the significant reduction in heart disease risk seen in a
meta-analysis of seven prospective studies. Of the more than 100,000 individuals who participated in these studies, those who
diets most frequently included onions, tea, apples and broccoli-the richest sources of flavonoids-gained a 20% reduction in their
risk of heart disease.
Quercetin, an antioxidant in onions, and curcumin, a
phytonutrient found in the curry spice turmeric, reduce both the size and number of
precancerous lesions in the human intestinal tract, suggests research published in Clinical Gasteroenterology and
Hepatology.
A compound newly identified in onions called gamma-L-glutamyl-trans-S-1-propenyl-L-cysteine sulfoxide (GPCS) inhibits
the activity of osteoclasts (the cells that break down bone). The more GPCS given in this animal study, the more the bone
resorptive (breakdown) action of osteoclasts was inhibited.
Onions may be especially beneficial for women,[citation needed] who are at increased risk for osteoporosis as they go through menopause. Fosamax (Alendronate), the drug typically prescribed to prevent
excessive bone loss, works in a similar manner, by destroying osteoclasts, so they do not break down bone. Potential negative
side effects of Fosamax include irritation of the upper gastrointestinal mucosa, acid regurgitation, esophageal ulcers and
erosions.
Several anti-inflammatory agents in onions render them helpful in reducing the
severity of symptoms associated with inflammatory conditions such as the pain and swelling of osteo- and rheumatoid arthritis,
the allergic inflammatory response of asthma, and the respiratory congestion associated with the common cold. Both onions and
garlic contain compounds that inhibit lipoxygenase and cyclooxygenase (the enzymes that generate inflammatory prostaglandins and
thromboxanes), thus markedly reducing inflammation. Onions' anti-inflammatory effects are due not only to their vitamin C and quercetin, but to other active components called
isothiocyanates. These compounds work synergistically to provide relief from inflammation. In addition, quercetin and other
flavonoids found in onions work with vitamin C to help kill harmful bacteria, making onions an especially good addition to soups
and stews during cold and flu season.
Onions and eye irritation
As onions are sliced, cells are broken, allowing enzymes called alliinases to break down sulfides and generate sulfenic acids (amino
acid sulfoxides). Sulphenic acids are unstable and decompose into a volatile
gas called syn-propanethial-S-oxide. The gas
diffuses through the air and eventually reaches the eye, where it reacts with the water to form a diluted solution of
sulfuric acid. This acid irritates the nerve endings in the
eye, making them sting. Tear glands produce tears to dilute and flush out the irritant.[6]
Supplying ample water to the reaction 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.[citation needed] Chilling or freezing onions prevents the enzymes from activating, limiting
the amount of gas generated. Using a sharp blade to chop onions will limit the cell damage and the release of enzymes that drive
the irritation response. Having a fire, such as a candle or a burner, will help as the heat and flames will draw in the onion
gas, burn it, and then send it up with the rest of the flame exhaust. In the heat, the chemical changes such that it no longer
irritates the eyes.
The volume of sulphenic acids released, and the irritation effect, differs among Allium species.
A firm in Toronto, Canada, attempted to utilize this property of onions in the manufacture of a form of tear gas for civilian use. It was marketed in 1991 but was unsuccessful as it had an effective shelf
life of only three months.[citation needed]
The characteristic odor of onions can be removed with lemon.[citation needed]
Propagation
Onions may be grown from seed or, most commonly, from sets. 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.
Either planting method may be used to produce spring onions or green onions, which are onions harvested while immature. Green
onion is a name also used to refer to Allium fistulosum, the Welsh onion, which is said not to produce dry
bulbs.
Varieties
|
|
|
Flower head of a yellow onion
|
|
- Bulb onion - Grown from seed (or onion sets), bulb onions range from the pungent varieties used for dried sooups and onion
powder to the mild and harty sweet onions, such as the Vidalia from Georgia or Walla Walla form Washington that can be sliced and eaten on a sandwich instead of
meat.
- Multiplier onions - Raised from bulbs which produce multiple shoots, each of which forms a bulb.
- Tree onion or Egyptian onion - Produce bulblets in the flower head; a hybrid of Allium cepas.
Shallots and ten other onion (Allium cepa L.) varieties commonly available in the United States were evaluated: Western
Yellow, Northern Red, 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.
Shallots had the most phenols, six times the amount found in Vidalia onion, the variety with the lowest phenolic content.
Shallots also had the most antioxidant activity, followed by Western Yellow, New York Bold, Northern Red, Mexico, Empire Sweet,
Western White, Peruvian Sweet, Texas 1015, Imperial Valley Sweet, and Vidalia.
Western Yellow onions had 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 contained, the more antioxidant and anti-cancer activity
they provided.
When tested against liver and colon cancer cells, Western Yellow, New York Bold 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.
Production trends
Top Ten Onions Producers — 2005
(1000 tonnes) |
China |
19,793 |
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] |
Onions in language
In the English vernacular, "an onion" is a difficult situation, the use stemming
from the onion's tendency to irritate or inflame the eyes.[citation needed] Conversely, the term "onion" can be
used to describe any state of being, as in the phrase, "[someone] really dices my onion!" It may also represent an object of many
layers.
In some Scots dialects, onion is pronounced 'Ingin'.
The expression "Layers of the onion" is used to describe a situation in which it is possible to go deeper and deeper revealing
seemingly similar layers until a central core is reached. It has been used as a metaphor in mysticism to describe the supposed
layers of reality. More recently, the phrase "Onions have layers, Ogres have layers!" is said by the character Shrek in the first
Shrek movie, by Dreamworks LLC, when he tries to
explain to his partner, Donkey, that he is a complex person.
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In other languages too the onion has acquired different connotations, eg., amongst the Khasi tribe in North East India, Onion
or "piat" in the local dialect refers to someone who is present everywhere or in every social gathering.
References
External links
See also
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