The onion (Allium cepa), like garlic, is a member of the lily family. There are numerous forms and varieties of onions, as they are cultivated world- wide. Common varieties are white globe, yellow globe, red globe, and green. With globe onions, the part used is the ﬂeshy bulb, while with green or spring onions, both the long slender bulb and the green leaves are used.
Onions differ in their size, color, and taste. There are two main types of large globe-shaped onions: spring /summer and storage onions. Spring/summer onions are grown in warm-weather climates and have a characteristically mild or sweet taste. Included in this group are the Walla Walla, Vidalia, and Maui
Sweet onions. Storage onions are grown in colder- weather climates and, after harvesting, are dried out for a period of several months, during which they attain dry, crisp skins. They generally have a more pungent ﬂavor and are usually named by their color: white, yellow, or red. The Spanish onion is an example of a storage onion. Smaller onions also come in many types, such as the green or spring onion, chives, leeks, and shallots; and the pearl onion.
History of Onions
Onions originated in Central Asia, from Iran to Pakistan and northward into the southern part of Russia. Onions have been revered throughout time not only for their culinary use but also for their therapeutic properties. In fact, as early as the sixth century B.C.E., onions were used as a medicine in India. Although onions were popular with the ancient Greeks and Romans, they were often dressed with extra seasonings since many people did not ﬁnd them spicy enough.
Yet it was their pungency that made onions popular among poor people throughout the world, who could freely use this inexpensive vegetable to spark up their meals. Onions were a key component in the cuisines of many European countries during the Middle Ages and were even served as a breakfast food.
Early explorers to North America, including Christopher Column- bus, brought onions to the Western Hemisphere. The leading producers of onions today are China, India, the United States, the Russian Federation, and Spain.
Nutritional Highlights of Onions
Onions are a very good source of vitamins C and B 6, biotin, chromium, and dietary ﬁber. In addition, onions are a good source of folic acid and vitamins B 1 and K. A 100 gram serving provides 44 calories, mostly as complex carbohydrate, with 1.4 grams of ﬁber.
Health Benefits of Onions
Onions contain a variety of organic sulphur compounds that provide health beneﬁts. Like garlic, onions also have the enzyme allinase, which is released when an onion is cut or crushed, causing the conversion of trans-S- (1-propenyl) cysteine sulphoxide to the so-called lacrimatory, or crying, factor, propanethial S-oxide. Other constituents include ﬂavonoids (primarily quercetin); phenolic acids, such as ellagic, caffeic, sinapic, and p-coumaric; sterols; saponins; pectin; and volatile oils.
Although not nearly as valued a medicinal agent as garlic, onion has been used almost as widely. Onions possess many of the same positive effects as garlic (see “Garlic”). There are, however, some subtle differences that make one more advantageous than the other for certain conditions.
Like garlic, clinical studies have shown onions and onion extracts to decrease blood lipid levels, prevent clot formation, and lower blood pressure. Onions have also been shown to have a signiﬁcant blood sugar-lowering action, comparable to that of the prescription drugs tolbutamide and phenformin, which are often given to diabetics. The active blood sugar- lowering principle in onions is believed to be allyl propyl disulphide (APDS), although other constituents, such as ﬂavonoids, may play a signiﬁcant role as well.
Experimental and clinical evidence suggests that APDS lowers glucose by competing with insulin (also a disulphide molecule) for breakdown sites in the liver, thereby increasing the life span of insulin. Other mechanisms, such as increased liver metabolism of glucose and increased insulin secretion, have also been proposed.
Onion has historically been used to treat asthma, too. Its action in asthma is due to its ability to inhibit the production of compounds that cause the bronchial muscle to spasm and to relax the bronchial muscle.
In addition, an onion extract was found to destroy tumor cells in test tubes and to arrest tumor growth when tumor cells were implanted in rats. The onion extract was shown to be unusually nontoxic, since a dose as high as forty times that of the dose required to kill the tumor cells had no adverse effect on the host. In addition, shallots have been shown to exhibit signiﬁcant activity against leukemia in mice.
The liberal use of the Allium species, including garlic, leeks, and onions, appears particularly indicated, considering their healing effects for the major disease processes, such as atherosclerosis, diabetes, and cancer, that are dominant today.
How To Select And Store Onions
Globe onions should be clean and hard and have dry, smooth skins. Avoid onions in which the seed stem has developed. Also, avoid those that are misshaped and/or show evidence of decay. Green or spring onions should have fresh- looking green tops and a white neck. Yellowing, wilted, or discolored tops should be avoided. Onions should be stored at room temperature, away from bright light, and in an area that is well ventilated.
To best accomplish this goal, place them in either a wire hanging basket or a perforated bowl with a raised base so that air can circulate underneath. The length of storage capability varies with the type of onion. Those that are more pungent in ﬂavor, such as yellow onions, will keep longer than those with a sweeter taste, such as white onions, since the compounds that produce the sharp taste are natural preservatives as well.
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Green or spring onions should be stored in a perforated plastic bag in the refrigerator, where they will keep for about a week. All onions should be stored away from potatoes, as they will absorb their moisture and ethylene gas, causing them to spoil more readily.
The remainder of cut onions should be wrapped tightly in cling ﬁlm or stored in a sealed container. They oxidize quickly, so you will need to use them within one to two days. Cooked onions will maintain their taste best in an airtight container but still will hold their ﬂavor and freshness for only a day or two.
Do not store them in metal bowls or storage containers, as this will cause them to discolor. Peeled, chopped onions can be frozen, but this process will cause them to lose much of their ﬂavor.
Tips For Preparing Onions
Several of the sulphur-containing compounds of onions are responsible for producing tears when an onion is cut. The compound allyl sulphate, which is produced when sulphur compounds released by the onion’s ruptured cells are exposed to air, is especially irritating. To reduce the production of this compound, chill the onions for an hour or so before cutting.
Chilling will reduce the activity of the enzyme that produces the allyl sulphate. Also, always use a very sharp knife, and cut the onions while standing so your eyes will be as far away as possible.
Quick Serving Ideas for Onions
Onions can be eaten on their own, either steamed or boiled, although some people do eat raw sweet onions like apples. However, onions are usually utilized to ﬂavor and enhance other recipes.
Sauteed chopped onions can be added to almost any vegetable dish to enhance its nutritional content and taste.
For instant vegetarian chili, heat together 1 medium chopped sautéed onion with a 12-ounce/350-gram can of kidney beans, 12 ounces/350 grams of chunky tomato sauce, and 2 tablespoons olive oil, and season to taste with chili powder.
Combine 1 chopped red onion, 2 roma tomatoes, 2 avocados, and I jalapeno for an all-in-one guacamole salsa dip.
Place chunks of onion or small pearl onions on a skewer, either alone or with other vegetables, coat lightly with olive oil, and grill for approximately 10 minutes.
Onions contain small amounts of oxalate. Individuals with a history of oxalate—containing kidney stones should avoid over consuming them.