(Aubry-Lecomte ex O'Rorke) Baill.
Irvingia gabonensis is a species of African trees in the genus Irvingia, sometimes known by the common names wild mango, African mango, bush mango, dika or ogbono. They bear edible mango-like fruits, and are especially valued for their fat- and protein-rich nuts.
Distribution and habitat
It is planted in parts of this area, e.g. in south-western Nigeria and southern Cameroon, and also in Côte d'Ivoire, Ghana, Togo and Benin.
The tree is present in the tropical wet and dry climate zone. Dika grows naturally in canopied jungle, gallery forests and semi-deciduous forests. It grows at altitudes from 200–500 m with annual rainfalls from 1200–1500 mm. Supported temperature ranges from 20° to 38 °C under slightly shaded to very bright, clear skies. Deep soils with more than 150 centimetres (59 in) are needed with a moderate fertility and good drainage. pH can range from 4.5 to 7.5.
Irvingia gabonensis grows straight, up to a height of 40 metres (130 ft) and 1 metre (3 ft 3 in) in diameter. It has buttresses to a height of 3 metres (9.8 ft). The outer bark is smooth to scaly with grey to yellow-grey color. The crown is evergreen, spherical and dense. Leaves are elliptic, one margin is often a little rounder than the other, acuminate, dark green and glossy on the upside. Flowers are yellow to greenish-white in small panicles. The flowers are bisexual. The fruit is nearly spherical, green when ripe with a bright orange pulp. The stone is woody and contains one seed. Seedling germinates epigeally.
Irvingia gabonensis is pollinated by Coleoptera, Diptera, Hymenoptera and Lepidoptera. It flowers from March to June and has two fruiting seasons: from April to July and from September to October. Seeds are dispersed by specialized vertebrates as elephants and gorillas. By reducing the number of those animals, the spread and regeneration of dika decreases and it becomes dependent on human planting.
Humans eat the fruits fresh, leading to the misnomer, African mango. The fruits are processed into jelly, jam, juice and sometimes even wine. The pulp has also been used to prepare black dye for cloth coloration.
The seed coat has to be cracked open to get to the endosperm. Seeds, also called dika nuts, are eaten raw or roasted. Mostly however they are pounded to butter- or a chocolate-like block. Seeds can be pressed to produce an edible oil (solid at ambient temperatures) or margarine used for cooking. The oil can also be processed further to soap or cosmetics. The press cake can be used as cattle feed or as thickening agent for soup. Seeds can be ground or crushed and used as a thickening and flavoring agent in soups and stews. They can also be made into a cake called "dika bread" for preservation.
The trees are used in agroforestry systems to shade other crops, especially cocoa and coffee. They are also used to reduce erosion. Cities have started using them to shade streets, as shelter belts, or for beautification.
Thousands of tons of dika seeds are traded each year, mostly within Africa.
A review of clinical research on consuming dika for weight management found irregularities in testing methods and reporting. The study concluded, "Due to the paucity and poor reporting quality of the randomized clinical trials, the effect of I. gabonensis on body weight and related parameters are unproven. Therefore, I. gabonensis cannot be recommended as a weight loss aid. Future research in this area should be more rigorous and better reported."
Nutritional aspects of Irvingia gabonensis
Nutritive value of the kernels per 100 g edible portion, which corresponds to about 2918 kJ of energy:
Besides the mentioned components, kernels of Irvingia gabonensis contain traces of thiamine, riboflavin and niacin. The approximate fatty acid composition is myristic acid 33–70%, lauric acid 20–59%, oleic acid 1–11%, palmitic acid 2% and stearic acid 1%. The contained amino acids are reasonably balanced for human nutrition. Since lysine, tryptophan, valine, threonine, isoleucine and phenylalanine have high concentrations in the seed, first limiting amino acids are methionine and cysteine.
Unlike the pulp of some other Irvingia spp., the pulp of the fruit of Irvingia gabonensis tastes juicy and sweet and is eaten fresh. Nutritive value per 100g edible portion of fruit pulp, which corresponds to 255 kJ of energy: energy:
|vitamin C||7 mg|
Until some years ago, 90% of dika products were harvested from scattered, wild trees. Dika trees were not cultivated systematically, because it was believed, that it takes up to 15 years until a tree bears fruit. Although they were not planted, their occurrence is high because they were also rarely lumbered. In a plantation using marcots (air-layering plants), flower production was observed two to four years after planting. Germination from seeds is low and when they are not handled carefully, most fail. The seeds are mostly extracted by breaking them by hand.
The domestication of dika is in its early stages. Around 1990, vegetative propagation allowed mass replication and selection. Grafting, budding, air-layering, marcotting and cuttings are feasible when they are applied to young wood.
An elite germplasm bank should be built up. This germplasm could then be used for vegetative propagation to improve the farmers welfare with improved plant material. Farmers could also be supported in cultivation. Future breeding aims are: multiple bearing – carrying fruits several times a year, precocity – fruiting at younger age, split fruits – nuts which release the seed by themselves and good form – dwarfing is especially valued, because it simplifies harvest. Invention of a nut-cracking device would help the further dispersion of the tree. A selection for "drawability", which could be used by food technology seems probable.
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