Groundnut or peanut is a herbaceous annual plant of the leguminous branch, under-group of the butterfly-like family. 11 varieties exist, all of them originate from tropical America. The cultivated ones belong to the species Arachis hypogea.

The most important countries producing groundnut are India, the USA, Senegal, Nigeria, Argentina, China and the Republic of Congo.

The alternate leaves with 4 leaflets close during the night. The flowers grouped in small spikes are yellow or red striated; only the flowers close to the ground at the bottom part of the plant give fruits, which mature at 5-6 cm under the ground.
The fruits are egg-shaped pods or pods of oblong cylindrical shape, with 2-6 cm length and a grey yellowish colour, covered with a net of nerves in relief and containing 1 to 7 nuts, separated from each other by a narrowing shape of the pericarp. The nuts are usually ovoid and covered by a husk of pink or salmon colour. The inside of the pod is black at maturity.
The groundnut yields vary from 500 to 2.000 kg of pods per hectare.

Groundnuts may be attacked during growing or storage by a mushroom, the Aspergillus Flavus, which secretes toxins called ‘aflatoxins’ and between which the most common one, the ‘B1’ is particularly active and noxious again some animals (turkey and pig) and may also contaminate the cow milk.
This mushroom grows particularly well on materials rich in carbohydrates and could thus affect other oil seeds. To develop, it needs a relative moisture of 80% and a temperature ranging between 30 and 40°C; it is especially active on seeds with 15-30% moisture but does not develop on seeds with moisture below 8%.

For groundnuts, the most critical time is harvesting : any defect in drying before ensiling in tropical conditions and any increase in moisture afterwards may result in extremely bad consequences. Artificial drying, combined or not with natural drying, is thus required.
Aflatoxin may also starts on pierced or cracked nuts before collecting on the plant.

Aflatoxin, once present in a contaminated nut, remains in it and is found in the meal, where it represents a danger for animals. This toxin is resistant to very high temperatures, higher than the cooker’s, and is practically not soluble in hexane.
It is thus a must to avoid any condition that may favour its blooming and contaminated meals will be discarded as fertilisers.

• 17-32% of linoleic acid
  
• 45-65% of oleic acid
  
• 1-1.5% of gadoleic acid
  
• 9-13% of palmitic acid
  
• 3-6% of stearic acid
  
• 2-8% of arachidic acid
  
• 2% of behenic acid
  
• 2% of lignoceric acid
  
• Iodine Value : 85-100
  
• saponification value : 189-193
  
• melting point : -2°C
  
• titer : 28-32°C
  
• unsaponifiables : 0.2-0.8%

Process

Peanuts are available unshelled or decorticated. Once decorticated, it is difficult to store peanuts, which are beaten by insects.
The oil starts to acidify rapidly. On the other side decorticating allows to reduce the transport volume to 5/8.
Generally, peanuts are not decorticated except if foreseen to produce industrial non grade-food oil.

Decorticating is done either by corrugated rolls, or by pounding or by centrifugation; the shells are then separated from the nuts by ventilation. Groundnuts are then dehulled from their fine husks.

To obtain the oil from decorticated groundnuts, they will be cleaned and cracked before pre-expelling, and then cakes are cracked, heated and flaked before solvent extraction.

The crude oil is then refined with neutralising, bleaching and deodorising process.

End uses

Groundnuts have many applications.
A large amount of the produced peanuts are locally consumed; the peanuts are eaten crude or grilled, slightly roasted, they are used as appetisers and serve in industries like of the nougat.

‘Peanut butter’ is made by a preparation of crushed groundnuts, roasted and mixed with 5-7% of groundnut oil and salt.


Depending if dehulled or not, groundnut cakes are called ‘white cake’ or ‘brown cake’.
The bran made by hulls is an excellent animal feed because it contains 14 to 19% of oil and 22% of nitrogenated matters.
The cakes are called ‘shelled’ when they still contain a certain amount of shells and are used as fertiliser. Decorticated, they are used for animal feed.
The extracted meal is still very rich : 41 to 50% of protein content. Shells and hulls are used as fertilisers or as combustible feed for the boiler.

Groundnut oil is a non-siccative oil. Crude and fresh from first pressing, it has a low acidity and is often consumed as such.
Refined groundnut oil is an excellent food-grade oil; it has been consumed mainly as a salad oil or for cooking oil, and also as such or hydrogenated for margarine.
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