ONION - A USEFUL VEGETABLE

DR. S.M.ALAM
Dec 21 - 27, 2009

The onion (Allium cepa) is one of the oldest vegetables used by human beings since the time immemorial as a raw vegetable and seems to have been in cultivation several thousand years before Christ.

Onion is the largest produced vegetable around the world. It has special qualities, which add to taste and flavor to food hence is used in all our traditional cuisine and culinary preparation.

In addition, it is also relished in raw form with meals. Since it is consumed by all classes of people, therefore it has assumed a place of essential item in our daily food intake. The demand of onion is worldwide.

Onion is used for consumption in salad and in all curries (fried, boiled, backed), and in pickles. Onion is a basic kitchen item all over the world.

Onion is produced in at least 170 countries of the world. According to the United Nations Food and Agriculture Organization, there are estimated seven million acres of land in the world producing over 64 million tons of onion each year.

Pakistan is on the list of the leading onion producers of the world. China ranks first in world onion production followed by India, USA, Turkey, Pakistan, Russia, South Korea, Iran, Japan, Egypt, Spain, Indonesia, Vietnam, and Myanmar.

In Pakistan, onion is grown the year-round in all the four provinces and Azad Kashmir though Sindh produces almost half of the total onion, which is used for both local consumption and exports.

Onions are grown as a basic condiment for culinary purposes. The total area under onion cultivation in the country for the year 2007-08 was about 148.7 thousand hectares including Punjab (32.6 thousand hectares), Sindh (66.1), NWFP (11.9), and Balochistan (38.1).

Total production of onion in the country was 2055.7 thousand tons that include Punjab's 306.4 thousand tons, Sindh 833.5, NWFP 216.6, and Balochistan 699.2.

Per hectare yield of onion in the country was 13.8 tons per hectare. On hectare basis, the yield is low compared to other onion producing countries of the world. The reasons may be low seed quality, unbalanced use of fertilizers, low water, attack of various insect-pests, and poor agronomical practices.

Onions are grown in the country 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.

The crop is propagated most frequently by seed sown directly in the field. The plant to plant spacing maintained is 10 cm and row to row spacing 30 cm.

It is grown from May to October to November and November to March. Onions may also be grown from the transplants started in greenhouses or seed beds or from small bulbs. Onion takes about 100 to 110 days from sowing to harvesting throughout the country.

PESTS

The common diseases of onion are onion smut, blight, downy mildew, pink, rot, white rot basal rot, neck rot and smudge.

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 with the lowest phenolic content. Interestingly, Pakistan not only stands with world's top onion producing countries but also finds itself among countries having highest per capita onion consumption.

The annual consumption of onion in Pakistan is 7 kg per person per year, though the average onion consumption is approximately 10 kg per person world over. Turkey has the highest onion per capita consumption with an astounding 36.6 kg leaving behind Libya which has 32 kg per person per year consumption.

The onion has great medicinal value. 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 eaten on their own but usually act as accompaniment to the main course.

Depending on the variety, an onion can be sharp, spicy, tangy and pungent or mild and sweet. Onions pickled in vinegar are eaten as a snack. Onions are a staple food in Pakistan and are therefore fundamental to Pakistani 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.

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.

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, onion was such an important food that people would pay for their rent with onions and even give them as gifts.

Doctors were known to prescribe onions to relieve headaches, coughs, snake bite and hair loss. The onion was introduced to North America by Christopher Columbus on his 1492 expedition to Haiti. Evidence suggests that onions may be effective against the common cold, heart disease, diabetes, osteoporosis and other common diseases.

Onion provides health promoting photochemical and nutrients, which contain antioxidant compounds known as quercetin that help delay or slow oxidative damage to cells and tissue of body. Studies have shown that it also helps eliminate free redicals in the body to enable low-density lipoprotein oxidation to protect and regenerate vitamin E and to inactive the harmful chelate effects.

Onions are free from fat and sodium and contain 5% carbohydrate and 13% dietry fibre. An onion contains 60 calories. Onions contain anti-inflammatory, anti-cholesterol, anti-cancer, and anti-oxidant components such as quercetin.

Onion flavor, odor, and tear characteristics come primarily from sulphuric compounds in the vegetable.

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 propl 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 in an increase in the amount of insulin available to usher glucose into cells causing 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 many countries, not surprising, since chromium levels are depleted by the consumption of refined sugars and white flour products as well as the lack of exercise.

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 contribute 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 whose diets most frequently included onions, tea, apples and broccoli- the richest sources of flavonoids-gained a 20% reduction in their risk of heart diseases.

Onionsí 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.