The African Shea tree, scientifically known as Vitellaria paradoxa, is a traditional African food plant that holds significant cultural and economic value. The shea tree grows naturally in the wild in the dry savannah belt from Senegal in the west to Sudan and South Sudan in the east, and onto the foothills of the Ethiopian highlands. It occurs in 19 countries across the African continent, namely Benin, Burkina Faso, Cameroon, Central African Republic, Chad, Ethiopia, Ghana, Guinea Bissau, Ivory Coast, Mali, Niger, Nigeria, Senegal, Sierra Leone, South Sudan, Sudan, Togo, Uganda, Democratic Republic of the Congo, and Guinea. This article delves into the various aspects of this remarkable tree, from its botanical characteristics and uses to its cultural importance and the challenges it faces.
Shea Tree Fruits
Botanical Description
Vitellaria paradoxa, commonly known as the shea tree, shi tree, or vitellaria, is a tree of the family Sapotaceae. It is a deciduous tree, growing to a height of 10 to 15 meters, but can reach up to 25 meters. In its native country it would probably be described as small: the gnarled shea tree which grows to a height of 10 to 15 m. The lactiferous tree with its leathery leaves does not flower until it is 20 years old and only reaches maximum productive capacity at the age of 50 years, then remaining fully productive for more than 100 years. The green plum-shaped fruits, which become brown when they ripen, have a diameter of up to 4 cm.
The species has variously been known botanically as Vitellaria paradoxa, Butyrospermum parkii, and Butyrospermum paradoxum. Many botanical works from the late 19th and much of the 20th centuries used the name Butyrospermum parkii, which is still commonly found in the cosmetics trade. Vitellaria is a monotypic genus, i.e., it has only one species.
The common name is shíyiri (in N'Ko: ߛ߭ߌ߭ߦߌߙߌ) or shísu (ߛ߭ߌ߭ߛߎ, lit. "shea tree") in the Bambara language of Mali. In Hausa language the tree is called Kaɗe or Kaɗanya. The species name parkii honors Scottish explorer Mungo Park, who learned of the tree while exploring Senegal. He was presumably inspired by the African Bambara language in which sii means sacred. In honour of Mungo Park the scientific name of the shea tree is still Butyrospermum parkii (Latin: butyro = butter, spermum = seed).
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Cultivation and Growth
The shea tree is a plant of the drier lowland tropics, usually at elevations up to 600 meters, though it can also be cultivated at elevations up to 1,500 meters. It grows best in areas where annual daytime temperatures are within the range of 24 - 38°C, but can tolerate 18 - 43°C. The tree starts bearing its first fruit when it is 10 to 15 years old; full production is attained when the tree is about 20 to 30 years old.
Shea butter trees have been protected by farmers for many centuries in the West African savannah, particularly where cattle are scarce. Productive trees are retained when new fields are cleared, leading to areas in Sudan where more than 40% of the trees are Shea butter. Natural regeneration is favoured by fallow of at least 5 years. Shortening the fallow period leads to insufficient regeneration. In areas of cultivation, shea butter tree is found in association with annual crops, such as pearl millet, sorghum, groundnut, cotton, cassava, yams and vegetables.
The tree produces a taproot up to 1, occasionally 2 metres long; with shallow lateral roots that are concentrated at a depth of 10 cm and extend up to 20 metres outward from the tree; and secondary lateral roots growing downwards to the same depth as the tap root. Early stem growth is slow; branching occurs after 4 - 7 years. Leaf fall, flowering, flushing and the onset of fruiting occur during the dry season. About 25% of the flowers set fruit.
The Shea Fruit
The shea fruit consists of a thin, tart, nutritious pulp that surrounds a relatively large, oil-rich seed from which shea butter is extracted. The fruits resemble large plums 4 to 8 centimetres long weighing between 10 and 57 grams each. These fruits take 4 to 6 months to ripen; the average yield is 15 to 20 kg (33 to 44 lb) of fresh fruit per tree, with optimum yields up to 45 kilograms (99 pounds). Each kilogram of fruit gives approximately 400 grams (14 ounces) of dry seeds.
Shea fruits resemble green plums and have round and elongated or torpedo-like shapes. The pulp is mildly sweet with the texture of a ripe pear. Shea fruit are typically gathered and processed by locals and provide an important source of income for the people of the African sub-Saharan savanna. Shea fruits are rich in carbohydrates, protein and fat as well as potassium and antioxidant phenols.
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The fruit pulp has a high vitamin C (196.1 mg/100 g). 50 g of the pulp provides 332% of the recommended daily intake of children (4-8 years old), and 98% of that for pregnant women. The fruit's kernels are rich in fat (17.4-59.1 g/100 g dry weight).
The thin green layer of pulp surrounding the inner kernel can be eaten raw or cooked. It is used to make jams and jellies and added to baked goods. The pulp is also made into wine. The resulting butter is used as a cooking oil for frying, a baking fat, a taste enhancer for a local porridge known as “to,” and other dishes.
Shea Fruits
Uses of Shea Butter
Shea butter has many uses and may or may not be refined. In the West it is most commonly used as an emollient in cosmetics and is less commonly used in food. Throughout Africa it is used extensively for food, is a major source of dietary fat, and for medicinal purposes.
Shea butter is a suitable base for topical medicines. Its application relieves rheumatic and joint pains and heals wounds, swellings, dermatitis, bruises and other skin problems. The fat is used traditionally to relieve inflammation of the nostrils. The leaves are used to treat stomach-ache. Bark infusions have medicinal and antimicrobial properties, e.g. against dysentery. They are applied as an eyewash to counteract spitting-cobra venom.
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Shea butter is a vegetable fat obtained from the seed. Many cosmetic products, especially moisturizers, lotions and lipsticks, use it as a base because its high unsaponifiable matter content imparts excellent moisturizing characteristics.
Shea nut butter is used in foods primarily in confectionery products as a cocoa butter substitute. Shea nut butter is also used in various cosmetic applications where the primary exposure would be skin contact. Shea nut oil or shea nut butter is primarily the fat fraction of this nut.
Recent research indicates that shea nut butter does not contain any detectable protein residues and does not contain detectable residues of proteins from peanut or various known allergenic tree nuts (walnut, almond, pecan, hazelnut). Since allergens are proteins, this research indicates the absence of detectable allergens in shea nut butter. Thus, refined shea nut butter does not pose any known or likely allergenic risk to consumers including individuals with pre-existing peanut or tree nut allergies.
Traditional Processing
Fat is traditionally extracted from the kernels by roasting and pressing them. The resulting liquid is boiled, sieved and cooled.
In rural areas, seeds are traditionally processed by hot water extraction, a task usually the responsibility of women. The fruit pulp is first removed for food, or by fermentation or boiling. The seeds are then boiled and later sun- or kiln-dried. Seeds are cracked using mortar and pestle, or stones; the kernels are removed by trampling and redried before being crushed, ground and kneaded to form a paste; the paste is put in water, heated or boiled and the boiling mass is churned until a grey, oily fat separates from the emulsion. The fat is skimmed off from the surface and washed to remove impurities.
This traditional method of processing is inefficient and labour intensive. Mechanization of the various operations, in particular the use of hydraulic or continuous screw expellers or application of solvent extraction, will improve oil extraction efficiency considerably.
Processing Shea Butter
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Cultural Significance
The shea tree was given its name at the end of the 18th century by the Scottish explorer Mungo Park. In its Central African homeland the shea tree is the main source of fat for cooking and for skin care, the fruits are also eaten. As a sacred tree it is treated with particular respect. The harvesting of the fruits is therefore embedded in an ancient ritual called Begu. According to tradition only women are allowed to harvest the fruits of this sacred tree of the savannah. After this men are forbidden to lay a hand on the tree and are not allowed to fell it either.
Shea butter is not just a commodity in West Africa - it is an integral part of African culture and traditions. For centuries, women in Africa have used shea butter to protect their skin from the harsh sun, wind, and dust. The butter is also used in haircare to nourish and moisturize hair. Beyond its cultural significance, shea butter is also an incredibly powerful natural ingredient that offers numerous benefits for the skin and hair.
Agroforestry and Other Uses
The shea butter tree is valuable in agroforestry systems. It provides shade, helps prevent soil erosion, and contributes to biodiversity. The tree regenerates well, and is traditionally favoured and protected by farmers. As a result, it has played a significant role in soil and water conservation and environmental protection in semi-arid West Africa.
Low-quality shea butter, often mixed with other oils, is a base material for soap. Shea butter is also very suitable for making candles because of its high melting point. As a waterproofing agent, shea butter is used as daubing for earthen walls, doors and windows.
Conservation Status
Shea butter is increasingly in demand for use in skincare and as a substitute for cocoa butter in chocolate, putting Shea trees on the International Union for Conservation of Nature’s Red List of Threatened Species.
Table: Nutritional Composition of Shea Fruit Pulp
The following table summarizes the nutritional composition of shea fruit pulp:
| Nutrient | Value per 100g |
|---|---|
| Vitamin C | 196.1 mg |
| Fat (dry weight) | 17.4 - 59.1 g |
