(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 germinate 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 can eat the fruits fresh, thus the name African mango can refer to dika. 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. Compared to the seed the fruit is only a tiny resource.
The episperm of the fruit has to be cracked open to get to the seed. 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 which are used for cooking. The oil can also be processed further to soap, cosmetics or pharmaceuticals. The press cake can be used as cattle feed or as thickening agent for soup. Seeds can be ground or crushed and used as thickening and flavoring agent in soups and stews. This food-thickening property is thought[by whom?] to be caused by mucilaginous polysaccharides, which become more viscous with cooking and is called "drawability". They can also be made into a cake called "dika bread" for preservation. Various medicinal uses mostly depend on the bark and leaves. It is employed as a purgative, for gastrointestinal and liver conditions, for hernias and urethral discharge or for sores and wounds.
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.
Pharmaceutical and medicinal use
A small double-blind placebo-controlled study published in 2005 demonstrated that I. gabonensis resulted in greater weight-loss and improved blood-test results in obese human volunteers when compared with a placebo. According to the study, significant reductions took place in weight, waist circumference, hip circumference, and systolic blood pressure in subjects taking the Irvingia compared with the placebo. Despite overall weight-loss in this study there was not a significant reduction in body-fat percentage. This indicates that weight was lost from both adipose tissue and from lean body-mass and that these losses were proportionate to original body compositions.
A further, longer clinical trial published in 2009 reported both weight loss and percent body-fat loss.
However, a clinical review of these studies was done and published in 2013, by a group of researchers led by Igho Onakpoya, MD, at the Department of Complementary Medicine, Peninsula Medical School, University of Exeter in the United Kingdom.
They found irregularities in testing methods and reporting. The abstract to the study concludes " Due to the paucity and poor reporting quality of the RCTs, 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%, laureic 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|
The fruit pulp's flavor components include zingiberene and α-curcumene, ethyl and methyl esters of cinnamic acid, dodecanal and dodecanol. This results in spicy-earthy, fruity, wine-yeast flavor notes.
Until some years ago 90% of the dika products were harvested from scattered, wild trees. They were not especially planted, because it was believed, that it takes up to 15 years until a tree bears fruits. Although they were not planted, their occurrence is high because they were also rarely lumbered. In a plantation using marcots (air-layering plants) florisation was observed two to four years after planting. Dika has no history as managed crop, that is why not a lot experience is gathered upon cultivating it. Germination from seeds is low and when they are not handled carefully, most fail to germinate. In trials was observed that they already three to five years after planting. Harvesting fruits at the mature green stage and let maturate at 26°–29 °C were preferred in color and texture to those which naturally ripened on the tree. The seeds are mostly extracted by breaking the episperm by hand. Different techniques are common in different countries. Sometimes seeds are harvested from fresh fruits, sometimes they are left to ferment in the sun. All of the above techniques are very time consuming.
The domestication of Dika is in its early years. Around 1990 vegetative propagation started allowing mass replication and selection. Grafting, budding air-layering, marcotting and cuttings are feasible when they are applied on 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.
- "Irvingia gabonensis". AgroForestryTree Database. World Agroforestry Centre.
- Lost Crops of Africa. 2, Vegetables. Washington DC: National Academies Press. 2006. pp. 119–135. ISBN 0-309-10333-9.
- "Irvingia gabonensis". Ecocrop. Food and Agriculture Organization. 1993–2007.
- "Irvingia gabonensis (Aubry-Lecomte ex O'Rorke) Baill.". Plant Resources of Tropical Africa – Your guide to the use of African plants. Prota.
- Ngondi, Judith L; Oben, Julius E; Minka, Samuel R (2005). "The effect of Irvingia gabonensis seeds on body weight and blood lipids of obese subjects in Cameroon". Lipids in Health and Disease 4: 12. doi:10.1186/1476-511X-4-12. PMC 1168905. PMID 15916709.
- Ngondi, Judith L; Etoundi, Blanche C; Nyangono, Christine B; Mbofung, Carl MF; Oben, Julius E (2009). "IGOB131, a novel seed extract of the West African plant Irvingia gabonensis, significantly reduces body weight and improves metabolic parameters in overweight humans in a randomized double-blind placebo controlled investigation". Lipids in Health and Disease 8: 7. doi:10.1186/1476-511X-8-7. PMC 2651880. PMID 19254366.
- Oben, Julius E; Ngondi, Judith L; Momo, Claudia N; Agbor, Gabriel A; Sobgui, Caroline (2008). "The use of a Cissus quadrangularis/Irvingia gabonensis combination in the management of weight loss: A double-blind placebo-controlled study". Lipids in Health and Disease 7: 12. doi:10.1186/1476-511X-7-12. PMC 2330043. PMID 18377661.
- Onakpoya, Igho; Davies, Lucy; Posadzki, Paul; Ernst, Edzard (March 2013). "The Efficacy of Irvingia Gabonensis Supplementation in the Management of Overweight and Obesity: A Systematic Review of Randomized Controlled Trials". Journal of Dietary Supplements 10 (1): 29–38. doi:10.3109/19390211.2012.760508.
- "Irvingia gabonensis". Forest Products Laboratory Tech Sheet. United States Department of Agriculture.
- "Irvingia gabonensis (Aubry-Lecomte ex O’Rorke) Baill.". Protabase record display. Prota.