|Small Scale Processing of Oilfruits and Oilseeds (GTZ, 1989, 100 p.)|
|1. Oil Plants and their Potential Use|
|1.2 The major oil plants|
The groundnut, Arachis hypogaea, also known as the peanut or earthnut, is botanically a member of the Papilionaceae, largest and most important member of the Leguminosae.
Figure 5 Groundnut.
Source: E. A. Weiss, 1983 p. 103
Mainly native to warmer climates' groundnuts frequently provide food for humans or livestock, and, in the absence of meat, form a valuable dietary protein component. The groundnut originates from South America (most likely Bolivia), where a large number of wild species are known to exist. The oldest indications of groundnut cultivation are from the pre-Columbian native societies of Peru. By the time of Columbus, the crop was widely distributed in South and Central America and in the Caribbean. It was probably brought to West Africa from Brazil in the 16th century, from there to the African east coast and so to India. In Africa, groundnuts have become so deeply integrated into society, that traditional customs have arisen around the crop.
Groundnuts grow best at an average temperature of 27°C with 30°C being optimal for germination. Under sub-optimal temperatures, the vegetation period is lengthened by 1 to 2 months. The demand for sunlight is relatively low; a reason why in Africa it is often cultivated in mixed cropping systems together with maize and oil palms. Average annual rainfalls of 500 mm are sufficient for the cultivation. For early varieties, even 200 to 300 mm during the vegetation period are accepted (as in the Sahel region).
Africa normally produces between 25 % and 30 % of world groundnut production and roughly one third of world exports, with Nigeria, Senegal, Zaire and the Sudan (in that order for 1985) being the . main producers. Nigeria's leading role in Africa, however, has been put under pressure due to a general decline in agricultural production as a result of the crude oil boom. For groundnut oil, the country has even become the largest African net importer (13 000 tons in 1985). The most important exporting countries for groundnut oil are now Brazil, China and Senegal. The United States are basically a residual supplier to foreign markets, of which the European Economic Community is the most important.
The groundnut is an annual legume, and there is a wide variation in the types cultivated in particular localities. In general, there are two main types which are distinct in appearance: One is upright with an erect central stem and vertical branches, the other has numerous creeping laterals. The first is more commonly grown for mechanized production, the second under peasant farming systems.
Average yields of groundnuts in shells are about one ton per ha with Africa having the lowest results of 0.75 tons/ha and North America ranging over 3 tons/ha. The shells make up 30 % of the weight; the kernels, commonly known as peanuts, can contain up to 50 % oil (although the usual range is 40 % to 45 %) and 25 % to 30 % protein.
Groundnuts give a pleasant tasting oil for direct human consumption and is used as a salad oil or for cooking. The oil is also further processed to margarine or Vanaspati in India.
Improper handling after the harvest can cause the development of poisonous mycotoxins. Groundnuts are particularly susceptable to the development of aflatoxin. Although aflatoxin is insoluble in vegetable oil and is normally concentrated in the cake' impurities accompanying the oil might contain it. Groundnut processors should therefore be especially aware of the danger of aflatoxin.