PROTA, Introduction to Vegetable oils
PROTA 14, 2007. Plant resources of tropical Africa. vol. 14. Vegetable oils. ed. by H.A.M. van der Vossen & G.S. Mkamilo. Wageningen, PROTA Foundation- Backhuys - CTA. 237 p.
Choice of species
PROTA 14: ‘Vegetable oils’ describes the cultivated and wild plant species of tropical Africa which yield oils or fats, collectively called vegetable oils in this volume. They are water-insoluble substances, consisting of mixtures of triglycerides of fatty acids and also containing small amounts of other compounds, such as sterols and tocopherols, which are antioxidants and play important roles in biological processes. Oils are liquid and fats are solid or semi-solid at temperatures of 18–24°C.
Vegetable oils are important in human nutrition, providing energy, essential fatty acids and lipophilic vitamins. Traditional non-food applications are soap, lamp oil and lubricants. About 15% of all vegetable oils are used for the manufacture of various industrial and technical products. Vegetable oils constitute about 80% of the world’s natural oils and fat supply, the remainder is of animal origin.
PROTA normally assigns a single primary use and, where relevant, one or more secondary uses to all plant species used in Africa. PROTA 14: ‘Vegetable oils’ comprises only accounts of species of which oil is the main product. Cocos palm (Cocos nucifera L.) is primarily used as an oil crop, and thus it is treated in PROTA 14, but it has many secondary uses, e.g. the leaves are used for thatching and making baskets, the shell of the coconut is made into utensils or activated carbon, ‘coconut water’ from young fruits and the sap exuding from the cut-off stalk of the inflorescence are refreshing drinks. Cotton (Gossypium spp.) is the main example of a crop that is an important source of oil, but it is primarily a fibre crop and is treated in PROTA 16: ‘Fibres’.
Species of which the oil is used in tropical Africa but have another primary use are listed after the primary use vegetable oil species, and are fully described in other commodity groups. Some other well-known species included in this list are: Anacardium occidentale L. (cashew nut), Dacryodes edulis (G.Don) H.J.Lam (butter fruit tree), Persea americana Mill. (avocado) and Zea mays L. (maize).
Six species are treated which have two primary uses, including use as oil plant, and consequently will be described in two commodity groups. These species are: Arachis hypogaea L. and Glycine max (L.) Merr. (also treated in PROTA 1: ‘Cereals and pulses’), Brassica carinata A.Braun and Brassica juncea (L.) Czern. & Coss. (also in PROTA 2: ‘Vegetables’), Ongokea gore (Hua) Pierre (also in PROTA 7: ‘Timbers’) and Jatropha curcas L. (also in PROTA 11: ‘Medicinal plants’).
In PROTA 14: ‘Vegetable oils’ comprehensive descriptions are given of 40 important species. These major oil plants comprise most cultivated species, but also several wild or partly domesticated ones. The accounts are presented in a detailed format and illustrated with a line drawing and a distribution map. In addition, accounts of 8 species of minor importance are given. Because information on these species is often scanty, these accounts are in a simplified format. For another 17 species the information was too scarce to justify an individual treatment and they have only been mentioned in the accounts of related species.
Family: Apart from the classic family name, the family name in accordance with the Angiosperm Phylogeny Group (APG) classification is also given where it differs from the classic name.
Synonyms: Only the most commonly used synonyms and those that may cause confusion are mentioned.
Vernacular names: Only names in official languages of regional importance in Africa are included: English, French, Portuguese and Swahili. It is beyond the scope of PROTA to give an extensive account of the names of a species in all languages spoken in its area of distribution. Checking names would require extensive fieldwork by specialists. Although regional forms of Arabic are spoken in several countries in Africa, the number of African plant species that have a name in written, classical Arabic is limited. Arabic names are therefore omitted. Names of plant products are mentioned under the heading ‘Uses’.
Origin and geographic distribution
To avoid long lists of countries in the text, a distribution map is added for major species. The map indicates in which countries a species has been recorded, either wild or planted. For many species, however, these maps are incomplete because they are prepared on the basis of published information, the quantity and quality of which varies greatly from species to species. This is especially the case for wild species which are not or incompletely covered by the regional African floras, and for cultivated species which are only planted on a small scale (e.g. in home gardens). For some countries (e.g. Central African Republic, Chad, Sudan, Angola) there is comparatively little information in the literature. Sometimes they are not covered by recent regional or national floras and although species may be present there, this cannot be demonstrated or confirmed.
The oil content of the produce is given together with the fatty acid composition of the oil. The fatty acids are grouped as saturated and unsaturated fatty acids, and are listed in accordance with the length of the carbon chain. More complex fatty acids are described in some detail. They include fatty acids with epoxy, hydroxy, phenyl or oxy-groups. These are poisonous, but are important source materials in the chemical industry. Other chemical compounds characteristic of oils, including sterols and tocopherols, are also mentioned.
The most common fatty acids are:
|9,11,13-C18:3||eleostearic acid (trans bonds)|
The fatty acid composition of an oil largely determines its physical characteristics. Physical characteristics are only given where relevant.
Where applicable, other aspects of the food value of plants are mentioned. The analytical method used to determine the various elements of the nutritional composition considerably influences the values found. For this reason a few standard sources were used wherever possible and the sources are mentioned in the text. These sources are: the USDA Nutrient database for standard reference; McCance & Widdowson’s The composition of foods; FAO Food composition table for use in Africa.
A morphological characterization of the species is given. The description is in ‘telegram’ style and uses botanical terms. Providing a description for the general public is difficult as more generally understood terms often lack the accuracy required in a botanical description. A line drawing is added for all major species to complement and visualize the description.
Descriptions of husbandry methods including fertilizer application, irrigation, and pest and disease control measures are given under ‘Management’ and under ‘Diseases and pests’. These reflect actual practices or generalized recommendations, opting for a broad overview but without detailed recommendations adapted to the widely varying local conditions encountered by farmers. Recommendations on chemical control of pests and diseases are merely indicative and local regulations should be given precedence. PROTA will participate in the preparation of derived materials for extension and education, for which the texts in this volume provide a basis, but to which specific local information will be added.
The genetic diversity of many plant species in Africa is being eroded, sometimes at an alarming rate, as a consequence of habitat destruction and overexploitation. The replacement of landraces of cultivated species by modern cultivars is another cause of genetic erosion. Reviews are given of possible threats for plant species and of the diversity within species and reference is made to the IUCN red list of threatened species where relevant. Information on ex-situ germplasm collections is mostly extracted from publications of Bioversity International (formerly the International Plant Genetic Resources Institute - IPGRI).
The main objective of the list of references given is to guide readers to additional information; it is not intended to be complete or exhaustive. Authors and editors have selected two categories of references; ‘major references’ are limited to 10 references (5 for minor species), the number of ‘other references’ is limited to 20 (10 for minor species). The references listed include those used in writing the account. Where the internet was used, the website and date are cited.
- H.A.M. van der Vossen, Steenuil 18, 1606 CA Venhuizen, Netherlands
- G.S. Mkamilo, Naliendele Agricultural Research Institute, P.O. Box 509, Mtwara, Tanzania
- R.H.M.J. Lemmens, PROTA Network Office Europe, Wageningen University, P.O. Box 341, 6700 AH Wageningen, Netherlands
- L.P.A. Oyen, PROTA Network Office Europe, Wageningen University, P.O. Box 341, 6700 AH Wageningen, Netherlands
- A. de Ruijter, PROTA Network Office Europe, Wageningen University, P.O. Box 341, 6700 AH Wageningen, Netherlands