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The peanut or groundnut (Arachis hypogaea) is a species in the family Fabaceae (commonly known as the bean, pea or legume family).
The peanut was probably first domesticated and cultivated in the valleys of Paraguay. It is an annual herbaceous plant growing 30 to 50 cm (1.0 to 1.6 ft) tall. The leaves are opposite, pinnate with four leaflets (two opposite pairs; no terminal leaflet); each leaflet is 1 to 7 cm (⅜ to 2¾ in) long and 1 to 3 cm (⅜ to 1 inch) across.
The flowers are a typical peaflower in shape, 2 to 4 cm (0.8 to 1.6 in) (¾ to 1½ in) across, yellow with reddish veining. The specific name, hypogaea means "under the earth"; after pollination, the flower stalk elongates, causing it to bend until the ovary touches the ground. Continued stalk growth then pushes the ovary underground where the mature fruit develops into a legume pod, the peanut – a classical example of geocarpy. Pods are 3 to 7 cm (1.2 to 2.8 in) long, normally containing 1 to 4 seeds.
Because, in botanical terms, "nut" specifically refers to indehiscent fruit, the peanut is not technically a nut, but rather a legume. Peanuts are often served in a similar manner to true nuts in many western cuisines, and are often referred to as a nut in common English.
The domesticated peanut is an amphidiploid or allotetraploid, meaning that it has two sets of chromosomes from two different species, thought to be A. duranensis and A. ipaensis. These probably combined in the wild to form the tetraploid species A. monticola, which gave rise to the domesticated peanut. This domestication might have taken place in Paraguay or Bolivia, where the wildest strains grow today. Many pre-Columbian cultures, such as the Moche, depicted peanuts in their art.
Archaeologists have dated the oldest specimens to about 7,600 years, found in Peru. Cultivation spread as far as Mesoamerica, where the Spanish conquistadors found the tlalcacahuatl (the plant's Nahuatl name, whence Mexican Spanish cacahuate, Castillian Spanish "cacahuete," and French cacahuète) being offered for sale in the marketplace of Tenochtitlan (Mexico City). The peanut was later spread worldwide by European traders. In West Africa farmers were already cultivating a plant from the same family, the Bambara groundnut, which also grows its seed pods underground.
Although the peanut was mainly a garden crop for much of the colonial period of North America, it was mostly used as animal feed stock until the 1930s. In the United States, the US Department of Agriculture initiated a program to encourage agricultural production and human consumption of peanuts in the late 19th and early 20th centuries. George Washington Carver developed hundreds of recipes for peanuts during his tenure in the program.
The orange-veined, yellow-petalled, pea-like flower of the Arachis hypogaea is borne in axillary clusters above ground. Following self-pollination, the flowers fade and wither. The stalk at the base of the ovary, called the pedicel, elongates rapidly, and turns downward to bury the fruits several inches in the ground, where they complete their development. The entire plant, including most of the roots, is removed from the soil during harvesting. The fruits have wrinkled shells that are constricted between pairs of the one to four (usually two) seeds per pod.
Peanuts grow best in light, sandy loam soil. They require five months of warm weather, and 500 to 1,000 mm (20 to 39 in) of water.
The pods ripen 120 to 150 days after the seeds are planted. If the crop is harvested too early, the pods will be unripe. If they are harvested late, the pods will snap off at the stalk, and will remain in the soil. They prefer an acidic soil of preferably 5.9–7 pH.
Peanuts are particularly susceptible to contamination during growth and storage. Poor storage of peanuts can lead to an infection by the mould fungus Aspergillus flavus, releasing the toxic and highly carcinogenic substance aflatoxin. The aflatoxin-producing moulds exist throughout the peanut growing areas and may produce aflatoxin in peanuts when conditions are favourable to fungal growth.
Harvesting occurs in two stages: In mechanized systems, a machine is used to cut off the main root of the peanut plant by cutting through the soil just below the level of the peanut pods. The machine lifts the "bush" from the ground and shakes it, then inverts the bush, leaving the plant upside down on the ground to keep the peanuts out of the soil. This allows the peanuts to dry slowly to a little less than a third of their original moisture level over a period of three to four days. Traditionally, peanuts were pulled and inverted by hand.
After the peanuts have dried sufficiently, they are threshed, removing the peanut pods from the rest of the bush.
Cultivation in China
The peanut was introduced to China by Portuguese traders in the 17th century and another variety by American missionaries in the 19th century.
They became popular and are featured in many Chinese dishes, often being boiled. During the 1980s, peanut production began to increase so greatly that as of 2006, China was the world's largest peanut producer. A major factor in this increase was the household-responsibility system, which moved financial control from the government to the farmers.
CULTIVARS IN THE UNITED STATES
Thousands of peanut cultivars are grown, with four major cultivar groups being the most popular: Spanish, Runner, Virginia, and Valencia. There are also Tennessee red and white groups. Certain cultivar groups are preferred for particular uses because of differences in flavour, oil content, size, shape, and disease resistance. For many uses, the different cultivars are interchangeable. Most peanuts marketed in the shell are of the Virginia type, along with some Valencias selected for large size and the attractive appearance of the shell. Spanish peanuts are used mostly for peanut candy, salted nuts, and peanut butter. Most Runners are used to make peanut butter.
The various types are distinguished by branching habit and branch length. There are numerous varieties of each type of peanut. There are two main growth forms, bunch and runner. Bunch types grow upright, while runner types grow near the ground.
Each year, new cultivars of peanuts are bred and introduced. Introducing a new cultivar may mean changes in the planting rate, adjusting the planter, harvester, dryer, cleaner, sheller, and the method of marketing.
Cultivars of the Spanish group include 'Dixie Spanish', 'Improved Spanish 2B', 'GFA Spanish', 'Argentine', 'Spantex', 'Spanette', 'Shaffers Spanish', 'Natal Common (Spanish)', "White Kernel Varieties', 'Starr', 'Comet', 'Florispan', 'Spanhoma', 'Spancross', 'OLin', 'Tamspan 90', 'AT 9899–14', 'Spanco', 'Wilco I', 'GG 2', 'GG 4', 'TMV 2', and 'Tamnut 06'.
Cultivars of Runners include 'Southeastern Runner 56-15', 'Dixie Runner', 'Early Runner', 'Virginia Bunch 67', 'Bradford Runner', 'Egyptian Giant' (also known as 'Virginia Bunch' and 'Giant'), 'Rhodesian Spanish Bunch' (Valencia and Virginia Bunch), 'North Carolina Runner 56-15', 'Florunner', 'Virugard', 'Georgia Green', 'Tamrun 96', 'Flavour Runner 458', 'Tamrun OL01', 'Tamrun OL02' 'AT-120', 'Andru-93', 'Southern Runner', 'AT1-1', 'Georgia Brown', 'GK-7',and 'AT-108'.
Virginia group peanuts are either bunch or running in growth habit. The bunch type is upright to spreading. It attains a height of 45 to 55 cm (18 to 22 in), and a spread of 70 to 80 cm (28 to 31 in), with 80 to 90 cm (31 to 35 in) rows that seldom cover the ground. The pods are borne within 5 to 10 cm of the base of the plant.
Cultivars of Virginia type peanuts include 'NC 7', 'NC 9', 'NC 10C', 'NC-V 11', 'VA 93B', 'NC 12C', 'VA-C 92R', 'Gregory', 'VA 98R', 'Perry', 'Wilson, 'Hull', 'AT VC-2' and' Shulamit'
Tennessee Red and Tennessee White groups
Popular confections made from peanuts include salted peanuts, peanut butter (sandwiches, peanut candy bars, peanut butter cookies, and cups), peanut brittle, and shelled nuts (plain/roasted). Salted peanuts are usually roasted in oil and packed in retail-size plastic bags or hermetically sealed cans. Dry roasted salted peanuts are also marketed in significant quantities. Peanuts are often a major ingredient in mixed nuts because of their relative cost compared to Brazil nuts, cashews, walnuts, and others. Peanut butter has been a tradition on camping trips and the home due to its high protein content and resists spoiling. Large quantities are also used in the commercial manufacture of sandwiches, candy, and bakery products. Boiled peanuts are a preparation of raw, unshelled green peanuts boiled in brine and often eaten as a snack. More recently, fried peanut recipes have emerged, allowing both shell and nut to be eaten. Peanuts are also used in a wide variety of cosmetics, plastics, dyes and paints.
Dry roasted peanuts
Dry peanuts can be roasted in the shell or shelled in a home oven if spread out one layer deep in a pan and baked at a temperature of 350 °F or 177 °C for 15 to 20 min (shelled) and 20 to 25 min (in shell).
Throughout the region, many candies and snacks are made using peanuts as a base.
Another popular Israeli peanut snack, Bamba puffs, is similar in shape to Cheez Doodles, but are made of corn and flavoured with peanut butter.
Common Indonesian peanut-based dishes include gado-gado, pecel, karedok and ketoprak, all vegetable salads mixed with peanut sauce, and the peanut-based sauce for satay.
Peanuts are used in the Malian meat stew maafe. In Ghana, peanut butter is used for peanut butter soup nkate nkwan. Crushed peanuts may also be used for peanut candies nkate cake and kuli-kuli, as well as other local foods such as oto. Peanut butter is also an ingredient in Nigeria's "African salad".
Peanut powder is an important ingredient in the spicy coating for kebabs in Nigeria and Ghana.
Peanuts are used to help fight malnutrition. Plumpy Nut, MANA Nutrition, and Medika Mamba are high-protein, high-energy and high-nutrient peanut-based pastes developed to be used as a therapeutic food to aid in famine relief. The World Health Organization, UNICEF, Project Peanut Butter and Doctors Without Borders have used these products to help save malnourished children in developing countries.
Peanuts can be used like other legumes and grains to make a lactose-free milk-like beverage, peanut milk. Peanut milk is promoted in Africa as a way to reduce malnutrition among children.
Low-grade or culled peanuts not suitable for the edible market are used in the production of peanut oil for manufacturing. The protein cake (oilcake meal) residue from oil processing is used as an animal feed and as a soil fertilizer. Raw peanuts are also widely sold as a garden bird feed.
Peanuts have a variety of industrial end uses. Paint, varnish, lubricating oil, leather dressings, furniture polish, insecticides, and nitroglycerin are made from peanut oil. Soap is made from saponified oil, and many cosmetics contain peanut oil and its derivatives. The protein portion is used in the manufacture of some textile fibres. Peanut shells are used in the manufacture of plastic, wallboard, abrasives, fuel, cellulose (used in rayon and paper) and mucilage (glue). Rudolf Diesel ran some of the first engines that bear his name on peanut oil and it is still seen as a potentially useful fuel.
Peanut skins are a significant source of resveratrol, a phenolic under research for a variety of potential effects in humans.
A hypothesis of the development of peanut allergy has to do with the way peanuts are processed in North America versus other countries, such as Pakistan and China, where peanuts are widely eaten. According to a 2003 study, roasting peanuts, as more commonly done in North America, causes the major peanut allergen Ara h2 to become a stronger inhibitor of the digestive enzyme trypsin, making it more resistant to digestion. Additionally, this allergen has also been shown to protect Ara h1, another major peanut allergen, from digestion – a characteristic further enhanced by roasting.
Another hypothesis, called the hygiene hypothesis, states that a lack of early childhood exposure to infectious agents like germs and parasites could be causing the increase of food allergies.
Recent (2008) studies comparing age of peanut introduction in Great Britain with introduction in Israel appear to show that delaying exposure to peanuts can dramatically increase the risk of developing peanut allergies.
Results from some animal studies (and limited evidence from human subjects) suggest that the dose of peanuts is an important mediator of peanut sensitization and tolerance; low doses tend to lead to sensitization and higher doses tend to lead to tolerance.
Peanut allergy has been associated with the use of skin preparations containing peanut oil among children, but the evidence is not regarded as conclusive. Peanut allergies have also been associated with family history and intake of soy products.
Though the allergy can last a lifetime, another 2003 study indicates that 23.3% of children will outgrow a peanut allergy.
Some school districts in the United States have banned peanuts. There are experimental techniques which appear to have desensitized some allergic individuals. The most popular technique, oral immunotherapy, works to create desensitization in those allergic by feeding them small amounts of peanuts until their body becomes desensitized. Some progress is possibly being made in the UK, where researchers at Cambridge are studying the effectiveness of the desensitization technique.
Research indicates that refined peanut oil will not cause allergic reactions in most people with peanut allergies. However, crude (unrefined) peanut oils are strongly flavoured, and have been shown to contain protein, which may cause allergic reactions. In a randomized, double-blind crossover study, 60 people with proven peanut allergy were challenged with both crude peanut oil and refined peanut oil. The authors conclude, "Crude peanut oil caused allergic reactions in 10% of allergic subjects studied and should continue to be avoided." They also state, "Refined peanut oil does not seem to pose a risk to most people with peanut allergy." However, they point out that refined peanut oil can still pose a risk to peanut-allergic individuals if oil that has previously been used to cook foods containing peanuts is reused.
Contamination with aflatoxin
UNITED STATES DEPARTMENT OF AGRICULTURE PROGRAM
George Washington Carver is often credited with inventing 300 different uses for peanuts (which, contrary to popular belief, did not include peanut butter but did include salted peanuts). Carver was one of many United States Department of Agriculture (USDA) researchers who encouraged cotton farmers in the South to grow peanuts instead of, or in addition to, cotton, because cotton had depleted so much nitrogen from the soil, and one of the peanut's properties as a legume is to put nitrogen back into the soil (a process known as nitrogen fixation). Rising demand for peanuts in the early 20th century was due to a shortage of plant oils during World War I and the growing popularity of peanut butter, roasted peanuts and peanut candies. Peanut products originating around the early 20th century include many brands still sold today such as Cracker Jack (1893), Planters peanuts (1906), Oh Henry! candy bar (1920), Baby Ruth candy bar (1920), Butterfinger candy bar (1923), Mr. Goodbar candy bar (1925), Reese's Peanut Butter Cup (1925), and Peter Pan (peanut butter) (1928).
Although India and China are the world's largest producers of peanuts, they account for a small part of international trade because most of their production is consumed domestically as peanut oil. Exports of peanuts from India and China are equivalent to less than 4% of world trade. The major producers/exporters of peanuts are the United States, Argentina, Sudan, Senegal, and Brazil. These five countries account for 71% of total world exports. In recent years, the United States has been the leading exporter of peanuts.
The major peanut importers are the European Union (EU), Canada, and Japan. These three areas account for 78% of the world's imports. 75% of Canada's peanuts are imported from the United States. Two thirds of United States (U.S.) imports are roasted, unshelled peanuts. The major suppliers are Taiwan, Malaysia, Hong Kong, Mainland China, and Canada. The principal suppliers of shelled peanut imports are Argentina and Canada. Imports of peanut butter from Argentina are in the form of a paste and must be further processed. Other minor suppliers of peanut butter include Malawi, China, India, and Singapore.
Consumption of peanuts in the EU is primarily as food, mostly as roasted-in-shell peanuts and as shelled peanuts used in confectionery and bakery products.
The average annual U.S. imports of peanuts are less than 0.5% of U.S. consumption.
Georgia is the leading peanut producing state in the U.S., followed by Texas and Alabama, respectively. About half of all peanuts produced in the United States are grown within a 100 mi (160 km) radius of Dothan, Alabama. Dothan is home to the National Peanut Festival established in 1938 and held each fall to honour peanut growers and celebrate the harvest.
Ninety percent of India's production is processed into peanut oil. Only a nominal amount of hand-picked select-grade peanuts are exported. India prohibits the importation of all oil seeds, including peanuts.
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