The African walnut, Tetracarpidium conophorum, is well known in West and Central Africa, where it goes by many different names-conophor nut, ukpa, asala kaso, and ngak to name a few. This strong, rambling vine originates in the humid tropical forests of West and Central Africa.
Plukenetia conophora, also called Nigerian walnut, and conophore, is a climbing shrub in the genus Plukenetia. It is not related to the walnut, being so named because its nuts bear a superficial resemblance to the walnut. It is native to tropical western and central Africa from Togo to Congo and in Sierra Leone.
It is abundant in Nigeria, Cameroon, Republic of the Congo and Democratic Republic of Congo. It prefers rain-forest hedge in half-shady places; low bush; secondary forest; plantations at elevations from 250-1,400 m (820-4,590 ft). Although it is well recorded in Sierra Leone, it is apparently not indigenous to Sierra Leone, since it is not recorded in Liberia and Ghana.
Its presence in Sierra Leone is due to returning slaves for it is known to the Krio by its Yoruba (Nigerian) name. Plukenetia conophora is the only Plukenetia species native to West Africa or Central Africa.
It produces stems usually 3-15 m (9.8-49.2 ft) long, though they can be up to 30 m (98 ft) long. The seed is thin-shelled and about 25 mm (0.98 in) long.
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It is contained in a pod which may house;one shelled nut (single), two shelled nut (double) and three shelled nut. The walnut shells could be black or brown from the plant. The nut is whitish upon cracking from the shell.
Plukenetia conophora belongs to the family Euphorbiaceae in the order Malpighiales of angiosperms in the plant kingdom. Euphorbiaceae is a large family of flowering plants with about 300 genera and 7,500 species. Members of the family are generally called spurge. This family occurs mainly in the tropics, with the majority of the species in the tropical America and Indo-Malayan regions.
A large variety occurs in tropical Africa, but they are not as abundant or varied as in the two other tropical regions. The genus Plukenetia (Euphorbiaceae) is a pantropical genus of 19 species belonging to the tribe Plukenetieae of the subfamily Acalyphoideae. Three sections or species groups of genus Plukenetia have been recognized.
The two previously named genera, Tetracarpidium (synonym Angostylidium) and Hedraiostylus (synonym Pterococcus), are now treated as sections of Plukenetia. The monotypic Plukenetia sect. Tetracarpidium (Angostylidium) includes the African species Plukenetia conophora, while Plukenetia sect. Hedraiostylus (Pterococcus) comprises two African species (Plukenetia africana and Plukenetia procumbens) and one Asian species (Plukenetia corniculata).
Plukenetia conophora is an important crop due to its multiple uses. Plukenetia conophora is widely cultivated for its nuts, which are cooked and consumed as snacks and often served with corn or rice. In West Africa, especially in Nigeria and Sierra Leone, as well as in Central African countries such as Cameroon, the seeds provide income to the rural people thereby improving their economy.
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Besides its nutritious seeds which can be eaten raw or cooked or sold for cash, cocoa farmers grow the vine for the partial shade its high canopy provides to their cocoa orchards, protecting them from full sun. Another attraction is that, being a climber, the vine takes up no extra land on their farms.
“The natural habitat of the vine is the forest, but since nowadays it is not that easy to harvest inside the forest; smallholder farmers have therefore decided to integrate the vine into their cocoa agroforests, where they can see it, guard it and control the harvest of its valuable products,” says botanist René Jiofack, a doctorate student at the University of Kinshasa.
Jiofack coordinated an agroforestry and socioeconomic survey of the liana in six villages in Bafia and Kiiki districts in Central Cameroon, involving 35 smallholder farmers, 29 of them men. The collaborative research, whose findings were recently published in the journal Bois et Forêts des Tropiques, had partners from the World Agroforestry Centre (ICRAF), the University of Yaounde, Université Libre de Bruxelles and Cameroon’s Natural History Museum. The work was funded by the International Foundation for Science, Sweden.
The researchers found that farmers typically grew the walnut vines within diverse cocoa agroforestry systems. Because mature vines of the walnut are heavy-fully grown plants can attain a diameter of up to 17 cm- mango and African plum trees were used as hosts to support the climber. The walnut was abundant in the area surveyed, with about 14 plants per hectare, second only to mango at 19 trees per hectare.
All 93 retailers and wholesalers interviewed in Yaoundé city and its surroundings said they wished the supply of the African walnut was more steady, as there was a strong and ready market in the entire sub-region.
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“A 15-kg bucket of raw, unshelled nuts costs anywhere from 7,000 to 12,000 FCFA (US$10-18), depending on season and where it is bought. Around harvest time, small lots of 8 to 10 boiled seeds are sold for 100 CFA (around 15 US cents) but when supply goes down, the same 100 CFA will get you only 4-5 seeds,” says Jiofack.
A major hindrance to improved production of the African walnut, the researchers found, was the unavailability of planting material of the walnut; not a single nursery in the survey area sold its seedlings, and the only way farmers could obtain them was from neighbors who had germinated them from seeds.
“There are many improved techniques for grafting and seed germination that farmers and nursery owners can learn and apply to the African walnut,” says Dr. Zac Tchoundjeu, the Regional Coordinator for ICRAF-West and Central Africa, and Co-leader of the Centre's Global Research Project on Tree Domestication and Agroforestry Germplasm. “Research can also allow us to develop high-yielding varieties with the qualities the market desires. Furthermore, modern plant propagation methods, including tissue culture, could allow the rapid multiplication of uniform seedlings for farmers to plant on their fields,” he adds.
Tchoundjeu is keen to bring the African walnut into research that will unlock its potential to raise the incomes for farmers and communities. His two decades of work in West and Central Africa saw him awarded the 2012 National Geographic Society/Buffett Award for a lifetime contribution to conservation in Cameroon, specifically recognizing Tchoundjeu’s work on the participatory domestication of traditionally important forest tree species that were fast-disappearing. The work has allowed such trees to be grown on smallholder farms and bring nutritional, livelihood, and environmental benefits.
Already, more than 10,000 famers in West and Central African region are making a good living from the activities related to participatory tree domestication, with bush mango (Irvingia gabonensis), njansang (Ricinodendron heudelotii), bitter kola (Garcinia kola), kola nut, and the African plum tree (Dacryodes edulis) as some of the priority species.
In Cameroon many Rural Resources Centers-where farmers receive training in agroforestry, nursery management, tree domestication, use of microfinance and community infrastructure improvements-have annual incomes from the sale of improved indigenous fruit trees ranging from $20,000 to 30,000, indicating that tree domestication is a powerful tool for alleviating poverty in rural areas.
Tchoundjeu says value chain development work is needed that will allow farmers to reap just livelihood benefits from cultivating the vine. In addition, research into better processing and storage methods will allow a more steady supply and even pricing.
Although the African walnut is already contributing to the wellbeing of some households in parts of West and Central Africa, the new research represents a first step towards domestication of the ‘unconventional liana.’ This will open the way to the walnut’s serving as a true cash crop that contributes to the wellbeing of households, communities and the environment.
Benefits and Uses
Its seeds are rich in fat, nearly eighty percent of it polyunsaturated ‘good fat’ with proven cholesterol-lowering properties. Its bark and leaves are used in traditional medicine to ease dysentery and other diseases, and in Nigeria, its seeds are reportedly used to treat male infertility.
Demand in the sub-region is strong for the African walnut, Tetracarpidium conophorum, and the findings of a new survey in Cameroon reveal its huge potential to bring socio-economic and environmental gains. The survey also reveals areas needing research and intervention, such as seedling production, storage, processing and marketing.
Eaten boiled, it has a bitter aftertaste, usually observed upon drinking water. The seed can be ground into a powder and used with flour in making cakes. The nuts can also be roasted and eaten in the general diet, or added to cakes. The nuts are oil-bearing yielding 48-60% of a light golden colored oil with a taste resembling linseed oil.
Walnuts
Cultivation Practices
Tropical regions are the most suitable for planting walnuts. Planting walnuts on a large scale requires enough space to enable proper sunlight. There is no actual size of farmland for walnut plantation; however, ensure that your farmland can contain enough trees.
Growing African walnut requires adequate information. A knowledge of output per acre is required for large-scale farming. Transplanting of seedlings can occur after leaves come out. Transplant should be covered well with soil and done carefully to avoid shock.
Walnuts are evergreen, and their trees grow up to 25 - 38 meters (approx.
Transplant should be covered well with soil and done carefully to avoid shock. Watering reduces as the plant grows big.
Harvest mostly begin in late August. On ripening, walnuts fall off to the ground. African walnuts are best stored in a cool, dry place. It can last for weeks when stored properly.
Diseases Affecting Walnut Trees
- Anthracnose: symptoms are black lesions on leaves, lesions on shoots, the leaf becomes elongated and sunken. It is fungi.
- Walnut Blight: This is a bacterial disease that also affects walnut.
- Mosaic Virus: This is a viral disease that causes yellowing and dropping of leaves, and defoliation occurs prematurely.
Impact on Obesity and Inflammation
Tetracarpidium conophorum nuts are nutrient‐dense Nigerian snacks associated with weight regulation. This study explores the nuts' impact on adipose tissue gene expression associated with low‐grade inflammation.
Overweight and obesity is caused by disproportionate accumulation of white adipose tissue which is usually accompanied by a generalized change in the circulating levels of several adipokines. Against this background, the expression of key pro‐inflammatory factors, Leptin and TNF‐α and anti‐inflammatory proteins namely PPARγ and adiponectin in the adipose can be manipulated in favour of obesity reduction.
The foregoing indicates a possibility of suppressing the complications of obesity by modulation of its associated inflammation. It is in this wise, that the current study was undertaken.
However, the molecular mechanism of the anti‐obesity properties of the nuts is yet unknown, hence the need for the current study. It sought to understand at least in part, the molecular mechanism of the nuts anti‐obesity activity using the anti‐inflammatory pathway. In so doing, we studied the interaction of the extracts and fractions from the nut with key molecular targets of the inflammatory pathway in vivo and in silico.
In order to better understand the impact of bioactives in African walnuts on markers of low‐grade inflammation associated with obesity, that usually elicit the outset of its comorbidities such as cancers, the study was undertaken.
A study such as this, is relevance is sourcing drug compounds from natural products, with comparative advantage over the existing medication or that would serve as adjuncts to the existing medications, contributing to the needed mitigation of the looming global obesity epidemic.
Experimental Design and Results
Ethanol whole extract (EWE), ethyl-acetate fraction (EAF) and the resulting residue (RES) were orally administered once daily to MSG-induced obese rats for 6 weeks (n = 6). Afterward, the RNA synthesis of inflammation-associated genes was measured, and GC-MS ligands in the extract and fractions were docked against their protein products in silico.
The study found that in obese animals, PPAR-γ and Adiponectin expressions were down-regulated, while TNF-α was up-regulated, indicating an increased low-grade inflammatory process in adipose tissue. After 6-week oral treatments with EWE, EAF and RES, PPAR-γ and Adiponectin expressions increased significantly, while TNF-α expression decreased, suggesting the modulation of obesity-induced inflammation in adipose tissue.
The in silico molecular docking analysis identified four lead compounds likely responsible for the observed effect, namely 6-Isopropenyl-4,8a-dimethyl-4a,5,67,8,8a-hexahydro-1H-naphthalen-2-one, 9,12,15-Octadecatrienoic methyl ester (Z,Z,Z), 9,12,15-Octadecatrienoic acid and Hexanedioic acid, bis(2-ethylhexyl). Of these compounds, 6-Isopropenyl-4,8a-dimethyl-4a,5,67,8,8a-hexahydro-1H-naphthalen-2-one demonstrated the strongest affinity to the binding cavities of PPARγ (−7.3 kcal/mol), Leptin (−5.2 kcal/mol), Adiponectin (−7.1 kcal/mol) and TNF-α (−6.3 kcal/mol) and was better than the standard drug, Orlistat (−6.7, −4.4, −6.8 and − 4.5 kcal/mol, respectively).
The study reveals that T. Tetracarpidium conophorum nuts, TNF‐α1. Tetracarpidium conophorum is a 10-20 ft. climbing shrub cultivated for its nuts which are consumed as snacks, when in season, in Nigeria and tropical Africa who it is dominant, and hence the common name, African black Walnut.
How to Harvest and Process Black Walnut (don’t wash them!)
African Walnut (Plukenetia conophora)
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