There are many different varieties of onion, red, yellow, white, and green, each with their own unique flavor, from very strong to mildly sweet. Onions can be eaten raw, cooked, fried, dried or roasted. They are commonly used to flavor dips, salads, soups, spreads, stir-fry and other dishes.
Onions (Allium cepa) belong to the lily family, the same family as garlic, leeks, chives, scallions and shallots.There are over 600 species of Allium, distributed all over Europe, North America, Northern Africa and Asia. The plants can be used as ornamentals, vegetables, spices, or as medicine. There are over 120 different documented uses of the Alliums.
Onion and other Allium vegetables are characterized by their rich content of thiosulfinates, sulfides, sulfoxides, and other odoriferous sulfur compounds. The cysteine sulfoxides are primarily responsible for the onion flavor and produce the eye-irritating compounds that induce lacrimation. The thiosulfinates exhibit antimicrobial properties. Onion is effective against many bacteria including Bacillus subtilis, Salmonella, and E. coli. Onion is not as potent as garlic since the sulfur compounds in onion are only about one-quarter the level found in garlic.
The Value of Onions
The World Health Organization (WHO) supports the use of onions for the treatment of poor appetite and to prevent atherosclerosis. In addition, onion extracts are recognized by WHO for providing relief in the treatment of coughs and colds, asthma and bronchitis. Onions are known to decrease bronchial spasms. An onion extract was found to decrease allergy-induced bronchial constriction in asthma patients.
Onions are a very rich source of fructo-oligosaccharides. These oligomers stimulate the growth of healthy bifidobacteria and suppress the growth of potentially harmful bacteria in the colon. In addition, they can reduce the risk of tumors developing in the colon.
Chinese with the highest intake of onions, garlic, and other Allium vegetables have a risk of stomach cancer 40 percent less than those with the lowest intake. Elderly Dutch men and women with the highest onion consumption (at least one-half onion/day) had one-half the level of stomach cancer compared with those consuming no onions at all.
Western Yellow, New York Bold, and Northern Red onions have the richest concentration of flavonoids and phenolics, providing them with the greatest antioxidant and anti-proliferative activity of 10 onions tested. The mild-tasting Western White and Vidalia onions had the lowest antioxidant content and lowest anti-proliferative activity. The consumer trend to increasingly purchase the less pungent, milder onion varieties may not be the best, since the onions with a stronger flavor and higher astringency appear to have superior health-promoting properties.