Ground Nut (Peanut)

The fruit (pod, nut) of the Ground nut-peanut (Arachis hypogaea L.) is made of an external shell (or hull) (21-29%) and of the nut itself (79-71%), which consists of a thin hull ("skin", seed coat) (2-3%), the kernel (69-73%) and the germ (2.0-3.5%) (van Doosselaere, 2013). The term "peanut" may refer to the whole fruit (including the shell), to the kernel with its thin coat, or to the kernel without the thin coat. Peanuts are nutrient- and energy-rich products that are mainly used for food, but whole cull peanuts or decorticated peanuts are occasionally sold for feed. Like other peanut products, peanuts can be contaminated by aflaould be tested before being fed to livestock.

Peanut is an annual herbaceous plant growing to a height of 30 to 50 cm. The peanut plant can be erect or prostrate with a well developed taproot and many lateral roots and nodules. The leaves are opposite and pinnate with four leaflets; each leaflet is 1 to 7 cm long and 1 to 3 cm across. The flowers are 1.0 to 1.5 cm across, bright yellow or yellowish orange with reddish veining. They are borne in axillary clusters on the stems above ground and last for just one day. One to several flowers may be present at each node and are usually more abundant at lower nodes. The first flowers appear at 4 to 6 weeks after planting and maximum flower production occurs 6 to 10 weeks after planting. 8 to 14 days after pollination, a short stalk at the base of the ovary elongates to form a thread-like structure known as a "peg". This pushes the ovary down 5 to 8 cm into the soil, where it develops into a pod. Pods are 3 to 7 cm long, normally containing one to four seeds. Pods reach maximum size after 2 to 3 weeks in the soil, maximum oil content in 6 to 7 weeks, and maximum protein content after 5 to 8 weeks. The peanut crop matures after 7 to 9 weeks in the soil, maturity being measured by maximum levels of protein, oil, dry matter, and the presence of darkened veining and brown splotching inside the pod. Peanuts usually require a minimum of 100 to 150 days from planting to maturity depending on the variety. Flowering continues over a long period, and pods are at all stages of development at harvest. Pegs will eventually rot in the soil and the resulting loose pods are lost during harvest (Putnam, 1991).

About 41% of the world peanut crop is used for oil production, whereas 45% is used directly as human food (Fletcher et al., 2016). Peanut kernels, usually cooked or toasted, are appreciated worldwide as a flavourful snack food, nutritionally dense due to its high energy, protein and fat content. Peanuts are also the primary ingredient of many finished products such as peanut butter, confections, nutritional bars, and are used in numerous dishes (Davis et al., 2016). Peanuts are usually too valuable to be used as animal feed. However, whole or shelled peanuts, or even roasted peanuts are sometimes fed to livestock. In 2001, for instance, raw peanuts, in excess of the peanut quota in the USA, were sold on the feed market. Likewise, abnormal peanuts, or peanuts with a higher afla than that permitted by the food regulations, have been used as feed ingredients for cattle. Peanuts meant for oil production, or for the manufacture of confectionary or peanut butter may also be available for livestock (Myer et al., 2001; Hill, 2002). In the USA, it has been estimated that less than 1% of the annual production is fed as raw peanuts to cattle (Hill, 2002).