Peanuts (Arachis hypogaea)

Description

The peanut (Arachis hypogaea) is an annual herbaceous legume in the Fabaceae family, cultivated worldwide for its oil-rich seeds, commonly known as peanuts or groundnuts. Unlike most legumes, peanuts are remarkable for their geocarpy: after fertilisation, the fruit develops underground, giving rise to the characteristic subterranean pods.

The plant has a low, spreading or slightly erect habit, generally 30–60 cm tall. Stems are slender and branching, bearing pinnate leaves with four oval or elliptic leaflets of bright to medium green. The flowers are small, yellow, and typical of legumes, with a delicate papilionaceous structure. After pollination, a specialised stalk called a gynophore elongates, bends downward and penetrates the soil; the fertilised ovary at its tip then develops into a pod below the surface.

The pod is a thin, wrinkled, netted shell, usually containing one to four seeds. Each seed is coated with a thin reddish to brownish skin and encloses two large cotyledons, which form the edible kernel. Raw peanuts have a firm, somewhat waxy texture and a mild, beany aroma. With roasting, they develop a warm, intense, nutty and slightly sweet flavour, along with a rich, characteristic aroma that is central to their culinary identity.

Agronomically, peanuts are well adapted to warm climates and light, sandy or sandy-loam soils with good drainage. As a legume, they can fix atmospheric nitrogen, contributing to soil fertility in crop rotations. Nutritionally and culturally, peanuts occupy a central role in many food systems as a high-energy, protein-rich oilseed, used both as whole kernels and as raw material for peanut butter, peanut oil, flours, pastes and confectionery ingredients. Their combination of flavour, texture and nutrient density has made peanuts important in traditional cuisines, modern processed foods, and specialised nutrition products.

Botanical classification

• Common name: Peanut (groundnut)

• Clade: Angiospermae

• Order: Fabales

• Family: Fabaceae

• Genus: Arachis

• Species: Arachis hypogaea L.

Climate
Peanut is a legume typical of warm and warm–temperate climates, with long, sunny summers and no frost. It needs a relatively long growing period with mild temperatures, while it is sensitive to cold and strong temperature fluctuations in the early stages. Even light frosts can damage young seedlings and reduce the production of underground pods.

Exposure
The ideal exposure is full sun, which is essential for good flowering and for proper penetration of the gynophores into the soil (the pegs that carry the fruits underground). In shaded positions, plants become elongated, produce fewer flowers and form fewer pods.

Soil
Peanut grows best in light, loose soils, sandy or sandy–loam, well drained and easy to work. Soils that are too compact hinder gynophore penetration and regular formation of underground fruits. Medium–low fertility soils are preferable, with slightly acidic to neutral pH; waterlogging and root asphyxia should be avoided, as they favour rot and yield loss.

Irrigation
Irrigation must be regular but not excessive, keeping the soil moderately moist, especially during flowering, gynophore penetration and seed filling. Drought periods in these stages reduce pod number and size, while excess water increases the risk of collar diseases and underground rots. It is best to irrigate evenly, avoiding sharp swings in soil moisture.

Temperature
The optimal temperature range for germination and growth is generally between 20 and 30 °C. Values below about 15 °C strongly slow development and make plants more sensitive to stress and pathogens. Peanut tolerates summer heat well, provided there is no extreme drought; very low temperatures, especially around sowing or final ripening, are unfavourable.

Fertilization
As a legume, peanut can fix atmospheric nitrogen through symbiosis with rhizobia, so it requires only small amounts of mineral nitrogen, often limited to early growth. Phosphorus and potassium are more important, supporting rooting, flowering and seed filling. In poor soils, a moderate application of well–matured organic matter before planting is useful, avoiding excessive fertilization that would promote lush foliage at the expense of pod production.

Crop care
Crop care includes control of weeds by light hoeing, especially in the early stages, and maintaining a loose surface soil to favour gynophore penetration. Good crop rotation reduces the pressure of fungal diseases and nematodes. It is important to avoid soil compaction and heavy traffic during flowering and pod set, so as not to hinder fruit formation.

Harvest
Harvesting is carried out when most pods are mature, with well–filled seeds and shells turning yellow–brown. Maturity is often checked by sampling plants and examining the internal pod colour and seed firmness. Uprooting should be done when the soil is not too wet, to reduce pod losses; pods are then dried in a thin layer in a well–ventilated place until they reach a moisture content suitable for storage.

Propagation
Propagation is by seed, using sound, untreated peanuts (not roasted), either in-shell or shelled, carefully selected. Sowing is done in the field when the soil has warmed sufficiently, placing seeds in rows or hills and keeping enough distance between plants to allow canopy development and underground fruit formation. The use of high–quality seed with good germination is essential to obtain uniform stands and satisfactory yields.

Indicative nutritional values per 100 g

(dry roasted peanuts, unsalted – average values)

• Energy: ~ 560–600 kcal

• Water: ~ 1–3 g

• Total carbohydrates: ~ 15–20 g

• Dietary fiber: ~ 8–10 g

• Protein: ~ 24–26 g

• Total fat: ~ 48–50 g

  • SFA (saturated fatty acids): ~ 6–8 g

  • MUFA (monounsaturated fatty acids, mainly oleic acid): ~ 24–28 g

  • PUFA (polyunsaturated fatty acids, mainly linoleic acid): ~ 13–18 g

• Minerals: magnesium, phosphorus, potassium, zinc, copper, manganese

• Vitamins: niacin (vitamin B3), folate (B9), vitamin E, small amounts of thiamine (B1), vitamin B6

Values vary with cultivar, origin, degree of roasting and processing, but peanuts consistently show high energy density, high fat and protein content.

Key constituents

• Lipids (~ 50% of weight), with a predominance of unsaturated fatty acids (MUFA and PUFA)

• Plant proteins (~ 25%), with a relatively high overall protein density

• Dietary fiber, mainly insoluble

• Carbohydrates: starch and small amounts of simple sugars

• Minerals: magnesium, phosphorus, potassium, zinc, copper, manganese, iron

• Vitamins: niacin, folate, vitamin E, B-group vitamins

• Phytochemicals: phytosterols, phenolic compounds, resveratrol (in small amounts), and other antioxidants

Production process

• Cultivation

  • requires warm temperatures and a frost-free growing season

  • best in light, sandy or sandy-loam, well-drained soils

  • sown directly in the field, often in rotated systems to benefit from nitrogen fixation

• Flowering and pegging

  • yellow flowers develop above ground

  • fertilised flowers produce gynophores that bend and push the young pod into the soil (pegging)

  • pods then develop and mature underground

• Harvesting

  • when plants show signs of maturity (yellowing leaves; pods hardened, kernels fully formed)

  • plants are uprooted or lifted; pods are left to dry attached for a short period, then separated

• Drying and cleaning

  • pods dried to safe moisture levels

  • cleaning to remove soil, stones and foreign matter

• Shelling and processing

  • mechanical shelling to obtain kernels

  • optional roasting, blanching, grinding, pressing for oil, or milling for peanut butter and flours

• Quality control and packaging

  • monitoring for moisture, microbial load, aflatoxins and defects

  • packaging in suitable materials to protect from oxygen, light and humidity

Physical properties

• kernels: small, oblong to oval, cream-coloured cotyledons with thin reddish-brown skin

• texture (raw): firm, waxy, moderately hard

• texture (roasted): crisp to crunchy, becoming softer and more pasty when chewed

• high fat content leads to an oily mouthfeel and good lubricity in pastes and spreads

• low moisture content in properly dried peanuts → long shelf-life, but sensitive to oxidation

Sensory and technological properties

• flavour:

  • raw: mild, beany, slightly grassy

  • roasted: intense nutty, sweet, toasted notes; characteristic and strongly appealing

• aroma: develops markedly during roasting via Maillard reactions and lipid oxidation products

• texture:

  • as kernels: crunchy or crisp when roasted

  • in peanut butter or paste: smooth to slightly grainy, cohesive, spreadable

• technological behaviour:

  • excellent oil yield for pressing and extraction

  • good emulsifying and stabilising behaviour in spreads (with appropriate formulation)

  • forms stable pastes and confections when combined with sugars, cocoa, etc.

  • peanut flour and protein concentrates improve texture, flavour and protein content in baked goods and snacks

Food applications

• direct consumption as snack (roasted, salted, spiced, coated)

• peanut butter and other spreads

• peanut oil for cooking, frying and dressing

• inclusion in confectionery, chocolate bars, nougat, brittle, pralines

• ingredient in savoury dishes, sauces and stews (e.g. peanut sauces, curries, African and Asian traditional dishes)

• use of peanut flour and peanut protein in baked products, snack foods and high-protein formulations

• incorporation into granolas, cereal mixes and nutrition bars

Nutrition and health

Peanuts are a highly energy-dense food, supplying a combination of protein, unsaturated fats, fiber, vitamins and minerals.

Relevant aspects:

• Protein: peanuts are a strong source of plant protein and can support overall protein intake, especially in diets with limited animal protein; combining peanuts with cereals improves amino acid balance.

• Fats: the lipid fraction is rich in monounsaturated and polyunsaturated fats, notably oleic and linoleic acids, which, when part of a balanced diet, are generally considered favourable compared with high saturated fat intake.

• Fiber: contributes to satiety and supports digestive health.

• Micronutrients: peanuts provide niacin, vitamin E, folate, magnesium, potassium and zinc, which support energy metabolism, antioxidant defence and neuromuscular function.

However, because of their high calorie density, peanuts should be consumed in moderate portions, particularly in weight-management contexts. Salted, sugar-coated or heavily processed peanut snacks may also contribute excess sodium and added sugars.

Portion note

A common portion of peanuts as a snack or ingredient addition is about 20–30 g (roughly a small handful). In dietary planning, this portion is often considered an energy-dense fat/protein exchange and should be integrated accordingly into total daily energy intake.

Allergens and intollerances

• peanuts are one of the major food allergens globally

• allergic reactions can be severe or life-threatening (anaphylaxis) even at very low doses

• cross-contamination between peanuts and other foods is a critical concern in manufacturing and food service

• individuals with peanut allergy must strictly avoid peanuts and peanut-derived ingredients

• some people may experience digestive discomfort if consuming large quantities of peanuts or peanut products

Storage and shelf-life

• store peanuts in a cool, dry place, away from direct light and heat sources

• because of their high fat content, peanuts are prone to oxidative rancidity if exposed to oxygen, high temperatures or light for prolonged periods

• well-dried and properly packaged peanuts can have a relatively long shelf-life; refrigeration or freezing extends stability for shelled or ground products (e.g. peanut butter)

• peanuts and peanut products must also be monitored for mould and mycotoxins (notably aflatoxins), which can develop under warm, humid storage if quality and hygiene are inadequate

Safety and regulatory

• peanuts must be clearly declared as an allergen on labels when present in a food product, according to relevant regulations (e.g. EU, UK, US)

• maximum limits for aflatoxins (toxic metabolites from certain moulds) are strictly regulated; peanut producers and processors must monitor and control contamination

• peanut oil, flours and protein products must comply with general food safety rules, contaminant limits and hygiene standards

• in some specialised products (e.g. nutritional formulations, infant foods), use of peanut ingredients may be limited or specifically regulated

Labeling

Packaged peanuts and peanut-containing products typically indicate:

• product name (e.g. peanuts, roasted peanuts, peanut butter, peanut oil)

• clear allergen statement for peanut

• net weight

• country or region of origin (where required)

• best-before date

• storage instructions

• list of ingredients for multi-ingredient products, including added salt, sugar, oils, flavourings, etc.

• nutritional information panel

Troubleshooting

In food use

• rancid or “old” taste → likely fat oxidation; product improperly stored or too old; discard and use fresher peanuts

• hard or rubbery texture → moisture uptake during storage; may indicate poor packaging or humid environment

• digestive discomfort → excessive portion size, inadequate chewing, or individual sensitivity

In storage

• rancid odour → exposure to air, heat or light; product no longer suitable

• visible mould or off-smell → potential contamination; discard immediately

• insect infestation → storage in warm, unprotected conditions; requires disposal of product and improvement of storage practices

Main INCI functions (cosmetics)

Cosmetic ingredients derived from peanuts include peanut oil (Arachis hypogaea oil) and related fractions. Typical functions:

• emollient: softens and smooths the skin surface

• skin conditioning: contributes to skin comfort and suppleness

• possible carrier oil for lipophilic active ingredients in creams, lotions and massage oils

Because peanut is a strong allergen, its cosmetic use requires careful evaluation and clear labeling, especially for leave-on products.

Conclusion

The peanut (Arachis hypogaea) is a distinctive legume-oilseed with a unique underground fruit development and a central place in global food systems. Its seeds are energy-dense, rich in unsaturated fats and plant proteins, and highly valued for their flavour and functional properties in both savoury and sweet foods.

At the same time, peanuts are one of the most important food allergens, and their high fat content makes them sensitive to oxidation and quality loss if not properly handled. When used with appropriate portion control, good storage practices and clear allergen management, peanuts represent a nutritionally valuable and technologically versatile ingredient, bridging traditional cuisines, modern snacks, spreads and specialised nutrition.

Studies

Safety

Peanuts can cause allergic reactions or intolerance in some people.

Peanut studies

References__________________________________________________

(1) Pandey MK, Wang H, Khera P, Vishwakarma MK, Kale SM, Culbreath AK, Holbrook CC, Wang X, Varshney RK, Guo B. Genetic Dissection of Novel QTLs for Resistance to Leaf Spots and Tomato Spotted Wilt Virus in Peanut (Arachis hypogaea L.). Front Plant Sci. 2017 Jan 31;8:25. doi: 10.3389/fpls.2017.00025. PMID: 28197153; PMCID: PMC5281592.

Abstract. Peanut is an important crop, economically and nutritiously, but high production cost is a serious challenge to peanut farmers as exemplified by chemical spray to control foliar diseases such as leaf spots and thrips, the vectors of tomato spotted wilt virus (TSWV). The objective of this research was to map the quantitative trait loci (QTLs) for resistance to leaf spots and TSWV in one recombinant inbred line (RIL) mapping population of "Tifrunner × GT-C20" for identification of linked markers for marker-assisted breeding. Here, we report the improved genetic linkage map with 418 marker loci with a marker density of 5.3 cM/loci and QTLs associated with multi-year (2010-2013) field phenotypes of foliar disease traits, including early leaf spot (ELS), late leaf spot (LLS), and TSWV. A total of 42 QTLs were identified with phenotypic variation explained (PVE) from 6.36 to 15.6%. There were nine QTLs for resistance to ELS, 22 QTLs for LLS, and 11 QTLs for TSWV, including six, five, and one major QTLs with PVE higher than 10% for resistance to each disease, respectively. Of the total 42 QTLs, 34 were mapped on the A sub-genome and eight mapped on the B sub-genome suggesting that the A sub-genome harbors more resistance genes than the B sub-genome. This genetic linkage map was also compared with two diploid peanut physical maps, and the overall co-linearity was 48.4% with an average co-linearity of 51.7% for the A sub-genome and 46.4% for the B sub-genome. The identified QTLs associated markers and potential candidate genes will be studied further for possible application in molecular breeding in peanut genetic improvement for disease resistance.

(2) Hu FB, Stampfer MJ, Manson JE, Rimm EB, Colditz GA, Rosner BA, Speizer FE, Hennekens CH, Willett WC. Frequent nut consumption and risk of coronary heart disease in women: prospective cohort study. BMJ. 1998 Nov 14;317(7169):1341-5. doi: 10.1136/bmj.317.7169.1341. 

Abstract. Objective: To examine the relation between nut consumption and risk of coronary heart disease in a cohort of women from the Nurses' Health Study....Conclusions: Frequent nut consumption was associated with a reduced risk of both fatal coronary heart disease and non-fatal myocardial infarction. These data, and those from other epidemiological and clinical studies, support a role for nuts in reducing the risk of coronary heart disease.

(3) Kris-Etherton PM, Hu FB, Ros E, Sabaté J. The role of tree nuts and peanuts in the prevention of coronary heart disease: multiple potential mechanisms. J Nutr. 2008 Sep;138(9):1746S-1751S. doi: 10.1093/jn/138.9.1746S. 

Abstract. Epidemiologic and clinical trial evidence has demonstrated consistent benefits of nut and peanut consumption on coronary heart disease (CHD) risk and associated risk factors. The epidemiologic studies have reported various endpoints, including fatal CHD, total CHD death, total CHD, and nonfatal myocardial infarct. A pooled analysis of 4 U.S. epidemiologic studies showed that subjects in the highest intake group for nut consumption had an approximately 35% reduced risk of CHD incidence. The reduction in total CHD death was due primarily to a decrease in sudden cardiac death. Clinical studies have evaluated the effects of many different nuts and peanuts on lipids, lipoproteins, and various CHD risk factors, including oxidation, inflammation, and vascular reactivity. Evidence from these studies consistently shows a beneficial effect on these CHD risk factors. The LDL cholesterol-lowering response of nut and peanut studies is greater than expected on the basis of blood cholesterol-lowering equations that are derived from changes in the fatty acid profile of the diet. Thus, in addition to a favorable fatty acid profile, nuts and peanuts contain other bioactive compounds that explain their multiple cardiovascular benefits. Other macronutrients include plant protein and fiber; micronutrients including potassium, calcium, magnesium, and tocopherols; and phytochemicals such as phytosterols, phenolic compounds, resveratrol, and arginine. Nuts and peanuts are food sources that are a composite of numerous cardioprotective nutrients and if routinely incorporated in a healthy diet, population risk of CHD would therefore be expected to decrease markedly.

 (4) Liu X, Hill AM, West SG, Gabauer RM, McCrea CE, Fleming JA, Kris-Etherton PM. Acute Peanut Consumption Alters Postprandial Lipids and Vascular Responses in Healthy Overweight or Obese Men. J Nutr. 2017 May;147(5):835-840. doi: 10.3945/jn.116.246785. 

(5) Park SH, Do MH, Lee JH, Jeong M, Lim OK, Kim SY. Inhibitory Effect of Arachis hypogaea (Peanut) and Its Phenolics against Methylglyoxal-Derived Advanced Glycation End Product Toxicity. Nutrients. 2017 Nov 4;9(11):1214. doi: 10.3390/nu9111214. 

Abstract. Methylglyoxal (MGO) is a highly reactive dicarbonyl compound that causes endothelial dysfunction and plays important roles in the development of diabetic complications. Peanuts are rich in energy, minerals, and antioxidants. Here, we report the potential beneficial effects of peanuts, and particularly the phenolic contents, against MGO-mediated cytotoxicity. Firstly, we optimized the extraction conditions for maximum yield of phenolics from peanuts by examining different processing methods and extraction solvents. To estimate the phenolic contents of peanut extracts, a simultaneous analysis method was developed and validated by ultra-high-performance liquid chromatography-tandem mass spectrometry. We found that roasted peanuts and their 80% methanol extracts showed the highest amount of total phenolics. Secondly, we evaluated the inhibitory effects of phenolics and peanut extracts against MGO-mediated cytotoxicity. Phenolics and peanut extracts were observed to inhibit advanced glycation end product (AGE) formation as well as to break preformed AGEs. Furthermore, pretreatment with peanut extracts significantly inhibited MGO-induced cell death and reactive oxygen species production in human umbilical vein endothelial cells. Peanut extracts prevented MGO-induced apoptosis by increasing Bcl-2 expression and decreasing Bax expression, and MGO-mediated activation of mitogen-activated protein kinases (MAPKs). In conclusion, the constituents of peanuts may prevent endothelial dysfunction and diabetic complications.

(6) Zhao Z, Wu M, Zhan Y, Zhan K, Chang X, Yang H, Li Z. Characterization and purification of anthocyanins from black peanut (Arachis hypogaea L.) skin by combined column chromatography. J Chromatogr A. 2017 Oct 13;1519:74-82. doi: 10.1016/j.chroma.2017.08.078.