|Allium cepa |
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. However, Zohary and Hopf warn that "there are doubts whether the A. vavilovii collections tested represent genuine wild material or only feral derivatives of the crop."
UsesOnions are found in a large number of recipes and preparations spanning almost the totality of the world's cultures. The whole plant is edible and is used as food in some form or the other. They are now available in fresh, frozen, canned, caramelized, 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. In European cultures 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, pungent, mild or 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 Australia, often served with cheese in the United Kingdom and are referred to simply as "pickled onions" in Eastern Europe. Onions are widely used in Iran and India and Pakistan, and are essential to daily life 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.
Onions are also used as an aromatic in cooking. In the classic mirepoix onion is used along with celery and carrots to flavor stocks, soups, stews and sauces.
Onions have particularly large cells that are readily observed at low magnification; consequently, onion tissue is frequently used in science education for demonstrating microscope usage.
Onion powderOnion powder is a spice used for seasoning in cooking. It is made from finely ground dehydrated onions, mainly the pungent varieties of bulb onions, which causes the powder to have a very strong odor.
Onion powder comes in a few varieties:
- White onion powder
- Red onion powder
- Yellow onion powder
- Toasted onion powder
Historical usesIt 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.
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.
The onion is easily propagated, transported and stored. The Ancient 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.
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. Doctors were known to prescribe onions to facilitate bowel movements and erections, and also to relieve headaches, coughs, snake bite and hair loss. The cultivated onion was introduced to North America by Christopher Columbus on his 1492 expedition to Hispaniola. However, they found that strains of wild onions already grew throughout North America. Native American Indians used wild onions in a variety of ways, eating them raw or cooked, as a seasoning or as a vegetable. Such onions were also used in syrups, as poultices, as an ingredient in dyes and even as toys. According to diaries of colonists, bulb onions were planted as soon as the Pilgrim fathers could clear the land in 1648. Onions were also prescribed by doctors in the early 16th century to help with infertility in women, and even dogs, cats 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.
Medicinal properties and health effects of onions
|Nutritional value per 100 g (3.5 oz)|
|Energy||166 kJ (40 kcal)|
|Dietary fiber||1.7 g|
|Vitamin A equiv.||0 μg (0%)|
|Thiamine (Vit. B1)||0.046 mg (4%)|
|Riboflavin (Vit. B2)||0.027 mg (2%)|
|Niacin (Vit. B3)||0.116 mg (1%)|
|Vitamin B6||0.12 mg (9%)|
|Folate (Vit. B9)||19 μg (5%)|
|Vitamin B12||0 μg (0%)|
|Vitamin C||7.4 mg (12%)|
|Vitamin E||0.02 mg (0%)|
|Vitamin K||0.4 μg (0%)|
|Calcium||23 mg (2%)|
|Iron||0.21 mg (2%)|
|Magnesium||0.129 mg (0%)|
|Phosphorus||29 mg (4%)|
|Potassium||146 mg (3%)|
|Sodium||4 mg (0%)|
|Zinc||0.17 mg (2%)|
|Percentages are relative to US recommendations for adults. |
Source: USDA Nutrient database
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. An application of raw onion is also said to be helpful in reducing swelling from bee stings. 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, while others found that they may act as an anti-inflammatory or bacteriostatic and can improve collagen organization in rabbits.
Onions may be especially beneficial for women, 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 that the pleiomeric chemicals in onions have the potential to alleviate or prevent sore throat. Onion in combination with jaggery has been widely used as a traditional household remedy for sore throat in India.
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), 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 reputed antioxidant and anticancer activity they provide. When tested against liver and colon cancer cells, 'Western Yellow' pungent yellow (New York Bold) and shallots were most effective in inhibiting their growth. The milder-tasting cultivars (i.e., 'Western White,' 'Peruvian Sweet,' 'Empire Sweet,' 'Mexico,' 'Texas 1015,' 'Imperial Valley Sweet,' and 'Vidalia') showed little cancer-fighting ability.
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.
3-mercapto-2-methylpentan-1-ol in onion was found to have an antioxidant potent that inhibits peroxynitrite-induced diseases.
Cultivated onionsSpanish onions come in three colors: yellow, red, and white. Yellow onions are full-flavored and are a reliable standby for cooking almost anything. Yellow onions turn a rich, dark brown when cooked and give French onion soup its tangy sweet flavor. The red onion, with its wonderful color, is a good choice for fresh uses or in grilling and char-broiling. White onions are the traditional onion used in classic Mexican cuisine. They have a golden color and sweet flavor when sautéed.
I'itoi onion (Allium cepa) is a prolific multiplier onion cultivated near Baboquiviri, Arizona. They have a shallot-like flavor. They are easy to grow and ideal for hot, dry climates. To grow them, separate bulbs, and plant in the fall 1 inch below surface and 12 inches apart. Bulbs will multiply into clumps and can be harvested throughout the cooler months. Tops will die back in the heat of summer and may return with monsoon rains; bulbs can remain in the ground or be harvested and stored in a cool dry place for planting in the fall. The plants rarely flower; propagation is by division.
Eye irritationcells are broken, allowing enzymes called alliinases to break down amino acid sulphoxides and generate sulphenic acids. A specific sulfenic acid, 1-propenesulfenic acid, formed when onions are cut, is rapidly rearranged by a second enzyme, called the lachrymatory factor synthase or LFS, giving syn-propanethial-S-oxide, a volatile gas known as the onion lachrymatory factor or LF. The LF gas diffuses through the air and eventually reaches the eye, where it activates sensory neurons, creating a stinging sensation. Tear glands produce tears to dilute and flush out the irritant. Chemicals that exhibit such an effect on the eyes are known as lachrymatory agents.
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. Another way to reduce irritation is by chilling, or 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. 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 can also be avoided by having a fan blow the gas away from the eyes as the onion is being cut.
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 reflexive actions of their eyes, such as blinking, with regard to irritation, as this is an ability useful when manipulating the lenses.
The amount of sulfenic acids and LF released and the irritation effect differs among Allium species. On January 31, 2008, the New Zealand Crop and Food institute created a strain of "no tears" onions by using gene-silencing biotechnology to prevent synthesis by the onions of the lachrymatory factor synthase enzyme.
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 of 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.
- 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 that 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; now known to be a hybrid of A. cepa × A. fistulosum, sometimes still treated as A. cepa var. proliferum.
- Welsh onion – Sometimes referred to as green onion or spring onion, although these onions may refer to any green onion stalk.
- Yellow onion - generally tapered ends, brown skin over the onion.
- Sweet onion - flatter ends and sold individually. Spanish and Vidalia
European onionsA number of onions have Protected Geographical Status in Europe, these include:
- Cipolla Rossa di Tropea, a red onion from Calabria, Italy (PGI)
- Cipollotto Nocerino, a spring/salad onion sized Allium Cepa from Campania, Italy (PDO)
- Oignon doux des Cévennes, a sweet onion from the south east of France (PDO)
StorageGreen onion and leeks are optimally stored refrigerated. Cooking onions and sweet onions, on the other hand, can be stored at room temperature, optimally in a single layer, in mesh bag in a dry, cool, dark, well ventilated location. In this environment, cooking onions have a shelf life of 3 to 4 weeks, and sweet onions 1 to 2 weeks. Cooking onions will absorb odours from apples and pears. Also, they draw moisture from vegetables they are stored with which may cause them to decay. Sweet onions have a greater water and sugar content than cooking onions. This makes them sweeter and milder tasting, but also reduces their shelf life. Sweet onions can also be stored refrigerated, where they have a shelf life of approximately 1 month, optimally uncovered. Irrespective of type, any cut pieces of onion are optimally tightly wrapped, stored away from other produce, and used within 2 to 3 days.
|Top Ten Onion Producers — 2008|
UN Food & Agriculture Organisation (FAO)
River Point Farms is America's largest grower, packer, shipper and processor of onions; including yellow, white, red, sweet and organic onions.