Nutritional and health benefits of onion (allium cepa)

Introduction

Onion is native of Asia and the Middle East and has been cultivated for over five thousand years. Onions were highly regarded by the Egyptians. Not only did they use them as currently to pay the who built the pyramids, but they also placed them in the tombs of kings, such as Tutankhamen, so that they could carry these gifts bestowed with spiritual significance with them to afterlife.

Onions have been revered throughout time not for their culinary use, but also for their therapeutic properties. As early as the 6^th century, owns were used as a medicine in India while they were popular with the ancient Greeks and Romans, they were often times dressed with extra seasonings since many people did not find them spicy enough. Yet, it was their pungency that made owns popular among poor people throughout the world who could freely use this inexpensive vegetable to spark up their meals. Onions were an indispensable vegetable in the cuisines of many European countries during the middle ages and later even served as a classic healthy breakfast food. Christopher Columbus brought onions to the West Indies, their cultivation spread from there throughout the Western Hemisphere. Today China, India the united states, Russian and Spain are among the leading producers of onion.

 Description of the plant

The onion known scientifically as “Allium Cepa” is on the surface, a humble brown, white or red, paper-thin skinned bulb, yet despite its plain looks, it has an intense flavour and is a beloved part of almost every region of the world.

The word onions come from the Latin word onion, which means “single or one”- reflecting of the plant producing a single bulb, unlike its cousin garlic that produces small bulb. The name also describes the onion bulb when cut down the middle, it is a union of many separate, concentrically arrange layers. Onion ranges in size, color and taste depending upon their variety. There are generally two types of large, globe-shaped onions, classified as spring/summer or storage onions, the former class includes those that are grown in warm weather climate and have characteristics mild or sweet taste example maui sweet onion, uldalia etc. Storage onion are grown in colder weather climates and after harvesting are dried out for a period of several months which allows them to attain dry, crisp skin. They generally have a more pungent flavor and are usually named by their color white, yellow or red. Spanish onion falls into by this classification.

Onions are a major source of polyphenols in general, and also of flavoniods. They can also vary greatly in their polyphenol and flavoniod content. In general, red onions are highly in total flavoniod than white onions.

 Tips for preparing and cooking

Cut onion into ¼ inch slice to cook them enough and quickly let them set for at least 5 minutes to help enhance their health promoting benefits. The substance that brings the eye to a tear or burn is a special gas that has been named lachrymatory factor (LF) (the full chemical names for this gas is propanthial 5-oxide, it is made from a naturally occurring compound in onion called 1-propenyl-L-cysteine sulphoxide).

If cutting onions irritates the eyes, there are a few tricks to overcome. Firstly use a knife and always cut the onions while standing, that way your eye is as far away as possible, consider cutting onions by an open window. If it really makes you cry consider wearing a goggle or glasses chill the onion for an hour or so before cutting this practice can slow down the onions metabolism and thereby lessen the rate of LF gas production. Cutting onions in cold, running water is a method that is often used to cut back on eye irritation, but it is a method we now as a second best choice since some of the nutrients found in onions can be lost into the flow of water.

How to select and store

Choose onion that is clean, well shaped, have no opening at those that are sprouting or have signs of mould.

In addition, onion of inferior quality often have soft spots moisture at their neck and dark patches which may all be indications of decay, when purchasing look for those that are fresh and the base should be whitish in colour. Avoid those that have wilted or yellowed tops. Onions should be stored in a well ventilated space at room temperature away from heat and bright light with the exception of green onions, do not refrigerate onions. Place them in a wire hanging basket or a perforated bowl with a raised based so that air can circulate underneath. The length of storage varies with the type of onion. Those that are more pungent in flavour such as yellow onions should be for about a month if stored properly. All onions should be stored away from potatoes as they will absorb their moisture and ethylene gas causing them to spoil more readily.

 Nutritional profile

The outstanding polyphenol content of onions is probably the most over looked nutrient of these alum vegetable. Among the flavoniods, onion also provides a particularly large amount of quercetin. A wide variety of allyl sulphides are found in including the four major diallyl sulphides, DMS (diallyl monosulfide), DDS (dially disulfide), DTS (diallyl trisulfide) and DTTS (dially tetrasulfide). Also present are a wide variety of sulfide including (i) s-methyl-L-cysteine sulfide (mcso), (+)-s-CI-Propennyl)-L-Cysteine sulfide (PRENCSO), S-Methyl-L-Cysteine Sulfide, s-propyl-I-cysteine sulfide and S-propenyl-L- cysteine sulfoxide.

Onions are a very good source of biotin, they are also a good source of manganese,  vitamin B6, copper, vitamin C, dietary fibre, phosphorus, potassium, folate and vitamin B1.

 Percentage composition of onion

Onion, chopped, cooked 1.00 cup (210.00 grams)

Calories     –        –        –        –        –        92%

GI    : 100

Nutrient

Biotin                   –        –        –        –       27%

Manganese        –        –        –        –        16%

Copper      –        –        –        –        –        16%

Vitamin B₆  –        –        –        –        –      16%

Vitamin C   –        –        –        –        –       15%

Fibre –        –        –        –        –        –        12%

Phosphorus        –        –        –        –        11%

Potassium –        –        –        –        –        10%

Vitamin B_{1  –               –               –               –}     8%

Folate        –        –        –        –        –        8%

Health benefits of onion

Onion like garlic, are members of the Allium family and both are rich in sulphur-containing compounds that are responsible for their pungent odours and for many of their health promoting effects.

1. Cardiovascular benefits

In animals studies, there is evidence that onions sulphur compounds may in an anti clothing capacity and help prevent unwanted clumping of blood platelet cells, onions sulphur compound can lower levels of cholesterol and triglycerides and also improve cell membrane function in red blood cells, I provides protection for the heart and blood vessels when consumed in a diet that is rich in other vegetables and fruits especially flavoniod and it also prevent the heart against heart attack.

2. Support for bone and connective tissues

From research it is said that onions can help increase our bone density and may be of special benefit to women of menopausal age who are experiencing loss of bone density, it is also evidence that women who have passed the age of menopause may be able to lower their risk of hip fracture through frequent consumption of onions.

3. Anti-inflammation benefits

While onions is not as well research as garlic in terms of specific inflammation health problems who rheumatoid, arthritis or allergic airway inflammation nevertheless it has been shown to provide important anti-inflammation benefit.

4. Cancer protection

It has been shown to reduce cancerous effects, when consumed in moderate amount. Colorectal cancer, laryngeal cancer and ovarian cancer are the type for which risk is reduced along with moderate amount of dietary onion for other cancer type including oesophageal cancer and cancer of the mouth. Daily intake of onions, is required before research results show significant risk reduction

5. It is used to treat cold
6. For the treatment of cough and bronchitis
7. It is also beneficial for the treatment of asthma
8. It is used to repel insects
9. In Chinese medicine onions have been used to treat angina, coughs, bacterial infection and breathing problem
10. It is used for the treatment of poor appetite and to prevent altherosclerosis
11. They can reduced the risk of tumours development in the colon
12. Onions are a very rich source of fructo-oligossaccharides which helps stimulate the growth of healthy bifidobacteria which suppresses the harmful bacteria in the colon.

Uses/ taxonomy

Onions have a universal appeal. They are safely consumed by most people. However, consuming large quantity of onion can lead to stomach distress and gastrointestinal irritation that may result in nausea, and diarrhoea. There are known interaction with drugs except that they can potentate the action of anti-coagulants.

Conclusion

Onion and other allium species are highly valued herbs possessing culinary and medicine value. Some of their beneficial properties are seen after long term usage. Onion may be a useful herb for the prevention of cardiovascular disease especially since they diminish the risk of blood clots. Onions also protect against stomach and other cancers as well as protecting against certain infections. Onions can improve lung function, especially in asthmatics. The more pungent varieties of onion appear to possess the greatest concentration of health promoting phytochemicals

References

Ali, M., Thomson, M. & Afzal, M. (2000). Garlic and onions: their effect on eicosanoid metabolism and its clinical relevance. Prostaglandins Leukot Essent Fatty Acids. 62(2),55-73.

Azuma, K., Minami, Y. & lppoushi, K. (2007). Lowering effects of onion intake on oxidative stress biomarkers in streptozotocin-induced diabetic rats. J Clin Biochem Nutr. 40(2),131-40.

Borjihan, B., Ogita, A. & Fujita, K. (2010) The Cyclic Organosulfur Compound Zwiebelane A from Onion (Allium cepa) Functions as an Enhancer of Polymyxin B in Fungal Vacuole Disruption. Planta Med. 2010 May 19.

Brat, P., George, S. & Bellamy, A. (2006) Daily Polyphenol Intake in France from Fruit and Vegetables. J. Nutr. 136,2368-2373.

Chun, O.K., Chung, S.J. & Song, W.O. (2007). Estimated dietary flavonoid intake and major food sources of U.S. adults. J Nutr. 137(5),1244-52.

Dorant, E., Brandt, P.A. & Goldbohm, R.A. (1996). A prospective cohort study on the relationship between onion and leek consumption, garlic supplement use and the risk of colorectal carcinoma in The Netherlands. Carcinogenesis 17(3):477-84.

Eady, C.C., Kamol, T. & Kato, M. (2008).  Silencing onion lachrymatory factor synthase causes a significant change in the sulfur secondary metabolite profile. Plant Physiol. 147(4),2096-1 06.

El-Aasr, M. Fujiwara, Y. & Takeya, M. (2010). Onionin A from Allium cepa inhibits macrophage activation. J Nat Prod. 73(7):1306-8.

Fukushima, S., Takada, N., Hori, T. & Wanibuchi, H. (1997) Cancer prevention by organosulfur compounds from garlic and onion. J Cell Biochem Suppl 27:100-5.