1.1 Characteristics of vegetable fats and oils

In principle, there are no essential differences between vegetable fats and oils. The distinction is only a question of melting points, fats being solid and oils being liquid at the temperature concerned.

Chemically, fats and oils are glycerides. A glyceride is a combination of glycerol with fatty acids, a so-called ester. This compound can be split up by naturally occurring enzymes, which are generally present in the rawmaterial, and by alkali. The latter reaction is, essential for the production of soap. In the case of enzymes, free glycerol and free fatty acids are formed, a process that also takes place when fats are digested in the human body.

The fatty acids found in vegetable fats and oils are generally based on 12 to 20 carbon atoms. They can be saturated or unsaturated. Saturated fatty acids contain only carbon atoms linked to not less than two hydrogen atoms; unsaturated fatty acids contain atoms with fewer hydrogen atoms, resulting in so-called double bonds,

The more common saturated fatty acids are referred to by name, e.g.:

- lauric	(C12)
- myristic	(C14)
- palmitic	(C16)
- stearic	(C18)
- arachidic	(C20)

The same applies for unsaturated acids, e.g.:

- oleic (C18) with one double bond (9:10),
- linoleic (C18) with two double bonds (9:10, 12:13),
- linolenic (C 18) with three double bonds (9:10, 12:13, 15:16).

Vegetable fats and oils have high calorific values and are therefore important sources of energy for the human diet. Besides, they contain so-called “essential" fatty acids (i.e. those necessary for good health) which animals cannot synthesize. Vegetable fats and oils also serve as carriers of the fat soluble vitamins, such as A, its provitamine Carotene, D, E (tocopherol) and K. Furthermore, fats and oils are, of course, important in giving taste to the food.

Fats and oils are relatively stable products. However, the quality of the fats or oils can be harmed by reactions which cause the formation of free fatty acids or rancidity. These reactions are caused by enzymes, air or moulds (so- called ketone rancidity). Fats can be split by active enzymes if the required reaction conditions are fulfilled (high temperature and high moisture content).

To prevent enzymatic reactions, oxidation and/or mould growth, vegetable oils and fats should be stored:

- at a relatively low temperature, - airtight,
- dry,
- clean and
- in the dark.

Proper storage can be in dry, clean containers such as bottles, tins or drums, filled to the top and well closed. To prevent oxidation, the oil should contain an antioxidant such as tocopherol (vitamin E). As mentioned above, tocopherol is to some degree - depending on the nature of the raw material - already present in unrefined oils and, thus, acts as a natural antioxidant.

When stored in this way, vegetable oils and fats have a “shelf life" (remain fresh) for at least six months.

1.2.1 Oil palm

Figure 2: Oil palm a) bunch, b) fruit of tenera (t), aura (d) and pisifera (p), Me = mesocarp, En = endocarp, Esp = endosperm.

Source: S. Rehm, G. Espig, 1984, p. 83

Botanically, oil palms are groups in the genus Elaeis, of which the major varieties are the African oilpalm (E. guineesis) and the American oilpalm (E. oleifera). Both can easily be crossed and give fertile hybrids.

Oil palms need an even temperature of between 24° C and 28° C; a reason why the cultivation is limited to the wet tropics about 10° north and south of the equator and below altitudes of 50° metres above sea level. Favourable conditions are annual rainfalls of 1500 to 3000 mm with dry seasons not exceeding three months.

Apart from tropical West-Africa, oil palms are mainly cultivated in South-East Asia and, as a later development, in Central and South America. Due to the introduction of new varieties, world production of oil palm fruit has at least doubled in the last decade as indicated by the growth in the production of kernels to 2.7 million tons in 1985 (see Table 1). Major producing countries of palm kernels are Malaysia (1.2 million tons), Nigeria (0.4 million tons) and Brazil (0.3 million tons). The world market for palm oil is dominated by Malaysia, Singapore and Indonesia, which have taken a market share of over 90 %; Africa as a whole only contributes 2 %.

Oil palms in a good growing condition carry in each leaf axil a flower from which a bunch (see Figure 2) with 1000 to 4000 egg-like, 3 to 5 cm long fruits can develop.

The majority of the oil is contained in the flesh of the fruit (mesocarp), about 12 % is in the inner nut (endosperm). According to the thickness of the nut shell (endocarp), three types are distinguished: aura with a shell thickness of 2 to 8 mm, tenera with 0.5 to 3 mm and pisifera without shell.

The selection of high-yielding types and the breeding of hybrid seeds (tenera is a cross between aura and pisifera) have increased the average yields of oil palms enormously. Wild growing bush palms in Africa used to give O.6 tons/ha of oil; current yields are more than 6 tons/ha and make the oil palm the highest-yielding oil plant. Hybrid seeds for tenera varieties, however, have to be produced in specialized seed centres. Aims of the breeders are, apart from a thin endocarp and and a thick mesocarp, to further shorten the unproductive growing period, to slow down and limit the height growth and to increase the fruit content.

The fruitpulp contains 56 % oil on average. As the ratio fruitpulp to nuts depends mainly on climate and variety, the oil content of the fruit (as a whole) varies widely in the range of:

- 14 % for aura fruit in a dry region,
- 20 to 27 % for wild or semi-wild aura fruit, and
- 36 % for tenera fruit.

Processing of the fruit is done as soon as possible after the harvest, because enzymes in the fruit react within 24 hours to form free fatty acids from the oil which substantially reduce the commercial value. The crude (red) palm oil contains a high level of 13-carotene and is an important source of vitamin A in the areas where it grows, preventing the disease xerophtalmia, that can cause blindness.

Palm oil for the world market is usually refined and used for the production of margarine or for other direct cooking purposes. Palm kernels contain 46 % to 48 % oil which is chemically quite similar to coconut oil, the use of which is described further below.

1.2.2 Coconut palm

The coconut palm, Cocos nucifera, is botanically grouped in the same subfamily Cocoideae as the oil palm. Although it is long since cultivated in all tropical regions, it originates from the South-West Pacific and South-East Asia; a region which is still the main producer.

For optimal growth, the coconut palm needs an average annual temperature of about 26° C with only small amplitudes between day and night. Therefore, even along the equator good yields are only realized below altitudes of 750 m. At sea level, the area of cultivation extends at least 150 north and south of the equator; in the Pacific it even reaches the subtropics. Where the plant depends on rainfall, 1250 to 2500 mm per year are seen as optimal. Good sunshine conditions are also necessary.

Figure 3: Coconut palm (a) unripe fruit with endosperm beginning to grow, (b) ripe fruit, (c) germ after 3 months, Me - mesocarp, EM = embryo, En = endocarp, Esp = endosperm, Kei = germ, Ha = “apple".

Source: S.Rehm, G. Espig, 1984, p. 87

World production of coconuts and copra (the dried, but otherwise unprocessed flesh of the nut) has only increased moderately over the last decade and currently stands at about 35 million tons. The "Far East" countries (including India and Sri Lanka) together with the Pacific region produce almost 90 % of this volume, Latin America and Africa share the rest about equally. Most important single producing countries are Indonesia (over 10 million tons p.a.) and the Philippines (about 8 million tons p.a.). For coconut oil, local demand is very high in Indonesia; therefore, the Philippines clearly are the leader in the market with a share of over 50 %. Africa as a whole contributes less than 3 %.

Apart from faster ripening and shorter stems, breeding efforts aim at resistance against diseases (e.g. Iethal yellowing which has done tremendous damage in the Caribbean). Crossings with so-called Malayan Dwarfs have given good results in this respect. Major pests are the rhinoceros beetle and a number of other leaf eating beetles and caterpillars.

The cultivation of coconut palms starts with planting the whole fruit, leaving just the upper end above the surface. On germination, the embryo forms a so-called “apple" (which is also consumed fresh). After about 4 to 5 months, the first roots leave the fibrous mesocarp. Planting distances for commercial plantation are about 9 m for high growing and 6 to 7 m for low growing varieties. Undercropping or double-use by grazing is common and can be the most economic land utilization.

A full-grown coconut palm yields 30 to 50 nuts per year with 8000 nuts per ha and year counting as a good harvest. Low growing hybrids usually have smaller nuts but can yield between 200 and 600 fruits per year.

To gain coconut oil, the fibrous husk is often separated from the nut. The nut is then split, usually with a bush knife, the flesh taken out and dried. Drying takes place in the open sun or in simple copra kilns which are fired with the coconut shells. The result is copra which has an oil content of 65 to 70 %. Maximum yields for new varieties are 9 tons of copra per ha, from which 6 tons of oil can be extracted. The actual extraction of the oil from copra is described in other chapters.

Coconut oil contains an extremely small percentage of unsaturated fatty acids. It therefore has a high melting point (22 to 26° C) and does not become rancid. It is therefore highly valued in warm climates and in others used for cakes and pastries. Other than for food purposes, the main use is quality soap.

1.2.3 Soyabean

Although not suited for small-scale extraction of the oil, the soyabean has, since 1945, become the most important source of both vegetable oil and protein and is therefore briefly characterized.

Figure 4: Soyabean.

Source: S. Rehm, G. Espig, 1984, p. 94

The soyabean or soyabean, Glycine max, is a member of the Papilonaceae, which includes some forty species of frequently twinning shrubs, distributed generally in the Asia and Australasia region. It is considered as having its origin in northeastern China, although the genus has two major centres. One is in eastern Africa, the second in the Australasian region with a secondary centre in China. From China soyabean spread to the neighbouring countries Korea, Japan and South-East Asia and finally around the world. As a cultivated crop it remained basically confined to Asia until the beginning of the century, when the USA developed soyabean into a major commercial crop.

The wet subtropics provide the best climate for the soyabean with average annual temperatures of around 25° C and optimal rainfall of 500 to 750 mm per year. The plant is extremely photoperiodic, with most varieties only flowering with day-light less than 14 hours a day. Day- light periods shorter than 12 hours lead to dwarf growth and reduced yields. All varieties are adapted to specific conditions. Cultivation of certain varieties is limited to particular geographic latitudes.

As shown in Table 1, the world production of soyabean has more than doubled in the last decade and a half and currently stands at over 100 million tons per year. The USA is the world's largest exporter, and together with China and Brazil, accounts for over 90 % of the world production (Africa: 0.2 %). Highest domestic consumption is in Asia, where it has been a basic food for centuries. Soyabean is mainly cultivated for its seeds commercially used for human consumption, stock food, and the extraction of oil. It is presently the world's most important grain legume in terms of total production and international trade.

The fruit is normally a short hairy pod, which can vary from 2 to 10 cm in length and 2 to 4 cm in width according to variety. The number of pods per plant can vary from a few dozen to several hundred, depending mainly on climatic conditions. They usually contain three, occasionally more, small, hard or ovoid seeds, usually between 5 and 10 mm in diameter. Seed weight varies considerably in the range of 5 to 40 g per one hundred seeds. The oil content of the seeds, as the major characteristic for the purpose of this booklet, varies between I 5 and 22 %, which is, at any event not sufficient for efficient extraction with small-scale technology.

Harvesting can be done by all methods from entirely manual to fully mechanized, depending on cost factors in a concrete context. In regions where labour is plentiful, plants are pulled by hand, thrown into heaps and threshed with sticks. In general, wind-rowing is not to be recommended, except in those circumstances where field conditions preclude natural drying, for instance in some West African areas.

Yields obtained range from 0.5 tons per ha in West and East Africa, 1.0 tons/ha in Central and southern Africa, 1.5 to 2 tons/ha in East Europe and most of Asia to an average in the USA of 2.5 tons/ha. These relatively low average yields should be judged against yields of nearly 6 tons/ha achieved by commercial growers in the USA, which also indicate the huge potential for increased production in tropical countries.

As mentioned earlier, the cultivation of soyabeans would never be economic without the double potential for vegetable oil and the protein-containing meal which accounts for 40% of the production value. Due to the low oil content, the modern process of solvent extraction is usually applied which, in turn, is only relevant for large- scale industrial operations.

Soya oil normally contains 10 % linolenic, 55 % oleic and 30 % linoleic acid with up to 50 % variation in a specific component. Without going into details, one might say that these components make the oil without further processing rather poor and unstable in flavour for direct human consumption. As an industrial rawmaterial, it is mainly used for the production of margarine.

Soyabeans contain a toxic factor which blocks the activity of the digestive enzyme trypsin. Before feeding whole seeds to pigs or poultry, this trypsin inhibitor should be destroyed by heating. Since soyabeans are normally heat treated during processing, oil cake is generally inhibitorfree.

1.2.4 Groundnut

The groundnut, Arachis hypogaea, also known as the peanut or earthnut, is botanically a member of the Papilionaceae, largest and most important member of the Leguminosae.

Figure 5 Groundnut.

Source: E. A. Weiss, 1983 p. 103

Mainly native to warmer climates' groundnuts frequently provide food for humans or livestock, and, in the absence of meat, form a valuable dietary protein component. The groundnut originates from South America (most likely Bolivia), where a large number of wild species are known to exist. The oldest indications of groundnut cultivation are from the pre-Columbian native societies of Peru. By the time of Columbus, the crop was widely distributed in South and Central America and in the Caribbean. It was probably brought to West Africa from Brazil in the 16th century, from there to the African east coast and so to India. In Africa, groundnuts have become so deeply integrated into society, that traditional customs have arisen around the crop.

Groundnuts grow best at an average temperature of 27°C with 30°C being optimal for germination. Under sub-optimal temperatures, the vegetation period is lengthened by 1 to 2 months. The demand for sunlight is relatively low; a reason why in Africa it is often cultivated in mixed cropping systems together with maize and oil palms. Average annual rainfalls of 500 mm are sufficient for the cultivation. For early varieties, even 200 to 300 mm during the vegetation period are accepted (as in the Sahel region).

Africa normally produces between 25 % and 30 % of world groundnut production and roughly one third of world exports, with Nigeria, Senegal, Zaire and the Sudan (in that order for 1985) being the . main producers. Nigeria's leading role in Africa, however, has been put under pressure due to a general decline in agricultural production as a result of the crude oil boom. For groundnut oil, the country has even become the largest African net importer (13 000 tons in 1985). The most important exporting countries for groundnut oil are now Brazil, China and Senegal. The United States are basically a residual supplier to foreign markets, of which the European Economic Community is the most important.

The groundnut is an annual legume, and there is a wide variation in the types cultivated in particular localities. In general, there are two main types which are distinct in appearance: One is upright with an erect central stem and vertical branches, the other has numerous creeping laterals. The first is more commonly grown for mechanized production, the second under peasant farming systems.

Average yields of groundnuts in shells are about one ton per ha with Africa having the lowest results of 0.75 tons/ha and North America ranging over 3 tons/ha. The shells make up 30 % of the weight; the kernels, commonly known as peanuts, can contain up to 50 % oil (although the usual range is 40 % to 45 %) and 25 % to 30 % protein.

Groundnuts give a pleasant tasting oil for direct human consumption and is used as a salad oil or for cooking. The oil is also further processed to margarine or Vanaspati in India.

Improper handling after the harvest can cause the development of poisonous mycotoxins. Groundnuts are particularly susceptable to the development of aflatoxin. Although aflatoxin is insoluble in vegetable oil and is normally concentrated in the cake' impurities accompanying the oil might contain it. Groundnut processors should therefore be especially aware of the danger of aflatoxin.

1.2.5 Sunflower

The sunflower, Helianthus annuus L., is a member of the Compositae, a large and successful family of flowering plants occurring throughout the world. The genus Helianthus is named from the Greek hellos meaning sun, and anthos flower.

Figure 6: Sunflower.

Source: KIT, 1979

Basically a temperate-zone plant, the main commercial production of sunflower is in the warm-temperate regions but breeding and selection have produced varieties adapted to a wide range of environments. Optimal conditions are short, hot (around 27ºC) summers with not too much rain (around 250 mm) during flowering and fructification. Greatest production is between latitudes of 200 to 500 north and 200 to 400 in the southern hemisphere, usually below altitudes of 1 500 m.

Sunflower is the only crop of worldwide commercial importance that originates from the area of the USA (probably south-western states to Mexico). Earlier used for food by the Indians of that region, it was already cultivated when the Europeans arrived in North America. The post-war introduction of Russian varieties, which not only pushed the oil content of the seeds to 50 % but were suitable for mechanized harvesting (90 to 150 cm high), had an immense impact on the development of sunflower as a commercial crop in Europe and the Americas.

Today, world production of sunflower ranks fifth among oil seeds and third among the vegetable oils (see Tables 1 and 2). In world trade, it has established an equally important position, although a significant portion of the production in developing countries is for personal consumption and therefore not registered. World production of sunflower seeds was dominated by the USSR which used to account for 50 %, but has declined since the 1970's to roughly half that share or 5 million tons in absolute terms. Other major producers are now Argentina (3.4 million tons), China (1.9), France (1.5) and the USA (1.4). Argentina has also become the leading exporter of sunflower oil and now accounts for almost half the world trade.

The cultivated sunflower is a tall, erect, unbranched, coarse annual, with a distinctive large, golden head. The plant grows rapidly, the stem varying in height from I to 3m when full grown with individual plants of giant varieties reaching 5m. New hybrids have a shorter stem and are remarkably even in growth and final height (within 5 % deviation). The discshaped head is born terminally on the main stem and branches where these occur and is commonly 10 to 30 cm in diameter.

- The fruit, or sunflower seed, ranges in colour from black through to white, but brown, striped or mottled seed can also occur. Seed varies greatly in size and weight, but is generally a compressed, flattish oblong. Average seed yields are currently 1.3 tons per ha, but can reach up to 4 tons/ha. The oil content of sunflower seed is between 25 and 48 %, but can reach 65 % under experimental conditions. Important for developing countries is the fact that high temperatures during seed development can reduce the total oil content to below 25 %, which would make small-scale processing less rewarding.

Sunflower oil, which is pressed in a cold stage, is a very highly valued salad oil; lower qualities are also used for technical purposes (paints).

1.2.6 Sesame

Sesame, Sesamum indicum L, member of the family Pedaliaceae, is probably the most ancient oilseed used by man and originates from the Ethiopian area. It occurs as numerous species and is locally known under a variety of names, such as gingerly and til in India, sim-sim in Arab countries and East Africa and benniseed in Nigeria.

Figure 7: Sesame. (a) shoot top with flowers' (b) ripe capsules.

Source: S.Rehm, G. Espig, 1984, p. 1 02

Sesame is considered a crop of the tropics and subtropics and normally requires fairly hot conditions, with temperatures around 26°C encouraging rapid germination, initial growth and flower formation. In altitudes below 1250 m, sesame's main distribution is between 250 north and south of the equator, but it can be found further north in China, Russia and the USA and further south in Australia and South America. Optimal rainfall is 500 to 650 mm per year, but since the crop is reasonably drought resistant it can also be planted in relatively arid zones with annual rainfalls as low as 300 mm.

World production of sesame seed has been almost static for 20 years, at 2.4 million tons per year (see Table 1) and almost exclusively originates in developing countries. Major producers are China, India, Burma and Tanzania (in that order for 1985). A large proportion of the sesame seed harvested is, however, neither marketed nor exported but consumed by local producers and therefore often does not appear in statistics for home production. This is particularly true in Africa, where sesame is grown from north to south, but often in such small plots that it is impossible to calculate the total, large though it may be. It is estimated that only 10 % of the total production enters world trade in sesame seed, the largest exporters being China, the Sudan and Mexico, the largest importers Japan, USA and Hong Kong.

Although reaching as high as 2 tons per ha (in Yugoslavia), average yields are only 350 kg of seeds per ha, because sesame is mostly cultivated in arid regions with poor soils. The average seed composition is 45 to 50 % (highly valued) oil and between 19 to 25 % protein. Sesame seed is relatively sensitive to mechanical damage, and even minor damage at threshing can result in an immediate loss of the viability of the oil extraction process.

1.2.7 Rape and mustardseed

Rapeseed and mustardseed are both obtained from species of Brassica in the family of the Cruciferae which includes some 160 species, mainly annual and biannual herbs. Of rapeseed, the two most important oilseed producers are B. campestris L., which has a fairly wide world distribution, and B. napus L., which is basically restricted to Europe and North Africa. Of mustardseed, B. juncea is the most common and known as Chinese or Indian mustard or rai. Because of the similarity of the species, the present chapter will refer to them as “rape" and summarize the characteristics.

Figure 8: Mustard.

Source: KIT, 1979

The origin of rape is most likely the South and East Asian region, since the oldest known references to its cultivation are from India, China and Japan. Secondary centres could be in the Mediterranean area. Whereas in the West and East, rape was originally cultivated for its roots and leaves (as a food), in India the seed was selected for its oil, and this started the wider distribution of the crop. Rapeseed's major use then became the production of oil for industry or domestic lighting. As an edible oil, rapeseed was initially only used by poor people, but the development of new technologies has increased its attractiveness for human consumption and animal feed. Mustardseed has long been used for spices.

Today, rapeseed and mustardseed rank with about 19 million tons sixth in world production of major oil plants and with 6 million tons fourth in vegetable oils (see Tables I and 2). Major seed producers are China, Canada, India and France (in that order for 1985), main oil producers are Europe, Canada and Japan. World trade in rape and mustard oils has been steadily increasing since the 1960's with volumes currently around 1.3 million tons. Surprisingly, with 75 % of the trade, exports are dominated by European countries (Federal Republic of Germany, France and others); other major producers, like Canada, are still increasing their market share. Production and exports from Africa are negligible, North African countries, in fact, importing one third of all commercially available quantities.

Oilseed rape and mustard are basically temperate crops which prefer moderate temperatures below 25°C during growth. Breeding and selection has considerably increased the geographic range of cultivation with hardy varieties being able to withstand long periods of snow cover and very low temperatures and others able to withstand more than 40°C for a limited period during the vegetative phase. Optimal rainfall is considered to be 700 mm per year. Rape will still produce a good crop using mainly residual soil moisture, provided some rain falls between planting and the seedling stage and at main flowering. These characteristics are of particular advantage in tropical regions of high altitude with significant temperature variations-and low rainfall.

Yields per ha can reach more than 3 tons of seeds under optimal conditions (Europe), but on average yields are just over 1.2 tons/ha. The protein content of the seeds varies from 10% to 45%, the oil content is normally in the range of 30 % to 50 %, but can reach up to 60%.

Rapeseed oil is dark, but after refining becomes light yellow and resembles sunflower oil. The colour is influenced by the seed chlorophyll level. A low value produces a light coloured oil which is commercially desirable. In the past, oil produced from the higher yielding varieties contained high levels of erucic acid, which constitutes a health risk for human consumption. Breeding has led to varieties without this acid. Oil from older varieties is mainly used for technical purposes.

1.2.8 Other oil-yielding plants

The sheanut or karite, Vitellaria paradoxa (syn.: Butyrospermum parkii), is a wild-growing tree in the countries south of the Sahel zone. The tree is relatively small, growing to a height of some 12 metres, having a thick trunk and a number of spreading branches which form a dense crown. It bears fruit after 10 to 15 years, reaching full bearing capacity at 20 to 25 years.

From Senegal to Sudan, the fruit, which requires 4 to 6 months to mature, is locally of substantial economic importance in particular for rural women who collect the nuts and process them to a butter-like edible substance. Average yield per tree is 15 to 20 kg of fresh fruit, with one third of the trees being productive each year. 50 kg of fresh nuts give 20 kg dry kernels which yield about 4 kg of shea butter.

The kernel of the nut contains 32 to 54 % fat. In international trade, shea butter serves as a cheaper substitute for cocoa butter and is in high demand when prices for the latter are up. It is also valuable for the cosmetic industry. With an estimated total production (collected nuts) of 500000 tons per year, Nigeria, Ghana, Ivory Coast and to a lesser extent, other countries in West Africa, are reported to export altogether about 30 000 tons.

Actual production and even export figures, however, are difficult to verify. In Mali, for example, production of kernels in the season 1985/86 is estimated to be 44000 tons, of which 10200 tons were officially exported. Inofficially, an estimated additional 16000 tons have left the country for unknown destinations.

Cotton, Gossypium spp., is basically a textile plant, which is mainly cultivated for its hair or lint (9.5 to 20 mm long) on the stem and leaves. Apart from the commercial value of the fibre, however, the seeds contain about 25 % oil thus making cotton the third most important oil crop. Of additional value is the protein-rich (40 %) oilseed cake, which gives a good protein supplement for cattle. The oilcake, however, can contain free gossypol, a pigment sometimes found in cottonseed. In this case, the use of the cake is limited to feeding to non-ruminants in small quantities.

World production of the seeds has exceeded 30 million tons in recent years, and of cottonseed oil between 3 and 4 million tons (see Tables I and 2). Major producers of cottonseeds are China, USSR and the USA. Although the plant originates from semi-arid zones in Africa, the continent as a whole (mainly Egypt and Sudan) only contributes 7 % to world production. World trade in cottonseed oil is dominated by the USA and Brazil. Due to the relatively low oil content of the seeds, solvent extraction is generally applied as a larger industrial operation; small-scale equipment does not appear to provide economic extraction.

Linseed, Linum usitatissimum L., is also mainly cultivated for its fibre, but is in multiple use as a spice and an oil yielding plant. World production in linseeds has considerably decreased over the last two decades and currently stands at about 2.5 million tons annually. The major producers are Canada and Argentina; production in Africa is negligible. Linseed oil is used mainly for technical purposes (paints) and faces heavy competition from other vegetable oils and in particular synthetic products. The market for the oil is more or less taken by Argentina (71 %) and the Federal Republic of Germany (17 %). Small-scale extraction is done in India.

Maize (Corn in American diction), Zeamays L., is basically a starch plant, but the oil content of the germ is also used on a commercial scale. The plant originates from Central and South America from where it began to spread to almost all parts of the world. Today, the USA is the largest producer, both American sub-continents together still contributing the majority (60 %) to the total world production. Maize oil is rather a minor byproduct of the maize starch manufacturing industry and is extracted on an industrial scale. World trade in maize oil amounts to about 300 000 tons annually, largest exporters being Europe and the USA. Africa accounts for net imports of some 10 000 tons a year.

Safflower, Carthamus tinctorius, originates from the eastern Mediterranean and the Persian Gulf and was first cultivated for the orange dye obtained from the florets. The seeds of modern varieties, however, contain 36 % to 48 % oil with good qualities for human consumption; a fact which now constitutes the main purpose for the cultivation of the plant whose seeds are suitable for small-scale processing.

The plant is a highly branched, herbeceous annual, varying in height from 30 to 150 cm and generally has yellow flowers. The fruit resembles a small, slightly rectangular sunflower seed, but with a thicker, more fibrous hull. It gives best yields (but with I ton/ha still low) in semiarid climates. Due to its fairly good drought and salt resistance, safflower is suitable for areas where other oil seeds are difficult to grow.

World production of safflower seed increased sharply in the 1960's but has since remained static at just below I million tons a year, with India accounting for more than half of the total. Safflower is still considered a typical small-holder crop and is mostly processed and consumed locally; for large plantations, as those in Mexico until recently, other oil seeds, particularly hybrid sunflower, appear to be more profitable.

Castor, Ricinus communis, is indigenous to eastern Africa, most likely originating in Ethiopia, but has a contemporary world-wide distribution in the warmer regions. Originally a tree with heights up to 10 m, most mechanically cultivated varieties today are short-lived dwarf annuals and only 60 to 120 cm high. Castor plants also grow wild in many countries and production could be substantially increased if incentives were sufficient. This is particularly so in eastern Africa, from the southern Sudan to southern Tanzania, where there are extensive areas with wild species.

Castor seeds (or “beans") almost exclusively originate from the developing countries, the major producers being China and Argentina. Although Africa does not play a major role in official statistics of world production (3 %), castor seeds might well be of greater economic significance in the local context. In world trade of castor oil, Brazil and India clearly dominate the supply side with a combined market share of over 90 %; largest importing region is Western Europe.

A large proportion of castor seeds on local markets in less developed regions is obtained from wild or semi-cultivated plants. At least in Africa, systematic cultivation of pure stands of castor by peasant farmers is the exception. More often castor is interplanted with other crops, sown along borders of fields, planted in areas unsuitable for other crops or merely protected when found growing naturally. In a cultivated stage, yields per ha are a mere 0.5 to I ton. The seeds, however, have a high oil content of 42 % to 56 % and are suited for small-scale processing methods. The oil is used for a variety of technical purposes.

Other oil yielding plants suitable for small-scale processing, which, for reasons of space cannot be dealt with in detail, include:

- Physic Nut (Purgier), Jatropha curcas, the oil of which is mostly used for soap and might be economically used as a fuel on the Cape Verde islands,
- Niger Seed, Guizotia abyssinica, which is produced in India and Ethiopia and gives a good edible oil,
- Babassu, Orbignya oliefera, originating from Brazil with nuts containing 2to 8 kernels with 60 % oil similar to coconut oil,
- Cohune, Orbignya cohune, growing in Central America, the nuts containing a kernel with 60 % oil comparable to coconut oil,
- Neem, Melia azadirachta L. (A-adirachta indica), growing in Africa, SE-Asia and India, with seeds containing 45 % oil, which is mainly used for soap and medical purposes,
- a large number of wild growing oil yielding plants of local importance.

1.3 By-products

In the above characterization of the major oil plants, reference has been made to the main use of the crops, i.e. in most cases the extraction of vegetable oil which, in turn, is used mainly for food and, to a lesser extent, for technical purposes.

In the present chapter, the by-products obtained from processing the above oilplants for oil are summarized (see Table 6).

Table 6: Important Oilcrops and their By-Products

Oilcrop or (intermediate) product	By-Product	Use
Oilpalm, fruit bunch
Oilpalm fruit Palm oil and	bunch fibrous residue and sludge	fuel fuel/fertilizer roughage traditionally for human consumption animal feed
Palmnuts
Palmkernels Palmkernel oil	shells palmkernel cake	fuel/charcoal animal feed
Coconut
Husked coconut	husks	coir for matting
Shelled -coconut	shells	fuel/charcoal
Coconut oil	coconut fibre (traditionally) or coconut cake	animal feed
Soyabean
Soyabean oil	soyabean cake	human consumption or anim (when trypsininhibitor free)al feed
Groundnut
Shelled groundnut Groundnut oil	shells groundnut cake	mulch/litter particle board human consumption or animal feed
Sunflower
Sunflower kernels	husks	fuel/filling material, polishing material, roughage
Sunflower oil	sunflower cake	animal feed
Sesame
Sesame oil	sesame cake	human food or animal feed
Rape/Mustard
Rape/Mustard oil	cake	animal feed
Castor bean		fertilizer
Castor oil	cake	if detoxified as animal feed
Cotton seed
Cotton seed oil	cake	animal feed (limited by free gossypol)

High protein containing oilcakes are much too rich to be fed directly to animals. They have to be mixed with starch and fibre containing feedstuffs in order to be properly digested. Handbooks on animal husbandry will provide detailed information on how a proper animal feed can be prepared with oilcakes as ingredients.

In Table 7, some examples are given of the composition of locally produced oilcakes of important oil seeds.

Table 7: Examples of the Chemical Composition of Oil Cakes fit for Animal Feed

1.4 Further processing

Vegetable oils and fats can be consumed directly or be the rawmaterial for further processing. Below, some of the more important products derived from vegetable oils are discussed. Most of these products are manufactured by a specialized industry.

Refined salad and cooking oils

In food, vegetable oils are normally preferred with a bright colour and a bland taste. Neutrally tasting salad and cooking oils are generally made from peanut, sunflower, sesame, maize or cotton seed oil by a complex refining operation which includes neutralization, bleaching and deodorization. Soyabean oil and rape seed oil are less suitable as they possess a characteristic flavour after deodorization.

Margarines

Margarines are an emulsion of fats in water, in which the water compound is dispersed as in butter made from milk. The fat needs to have a certain plasticity and to melt readily in the mouth. Such a fat is obtained by mixing, for instance, coconut and/or palmkernel oil with other oils which are hydrogenated to an appropriate degree.

As the product contains water it is easily spoiled by bacterial contamination or oxidation. Margarines need therefore to be tinned or stored under refrigeration.

Pure oils and fats can be kept much better. In India and other tropical countries butter is therefore processed into a pure oil, known as ghee.

Bakery products

Fat is a highly necessary ingredient in baked goods as it not only contributes to the flavour but also to the physical structure of the product. To provide the fats with the required so-called “shortening" value, a large range of special products are on the market for the bakery industry which are made by the hydrogenation of vegetable oils and compounding of fats from different origins.

Soaps

Soaps are commonly made by boiling a fat with strong Iye. The effectiveness of such a soap depends mainly on its surface activity properties and its solubility. Both depend largely upon the length of the chain and the unsaturation of the fatty acids which form the soap.

Soaps made from the higher fatty acids (e.g. stearic) are very efficient detergents, but have only limited solubility, which limits their usefulness as a household soap. Soaps of the lower fatty acids (e.g. Iauric acid) are freely soluble but are less efficient as a detergent.

An optimum balance can be reached on the basis of a fat from animal origin or palm oil, mixed with 15 % to 30 % of coconut or palmkernel oil.

Lubricants

Mineral oils have superseded “fatty" oils (i.e. animal and vegetable oils) as lubricants as they are more stable and cheaper. However, fatty oils have certain special advantages to mineral oils, since they have a superior ability to cling to metal surfaces in a thin film. Suitable fatty oils are those which are sufficiently saturated to be stable. They are used for lubricating light machinery. Castor oil is more viscous than ordinary oils and hence is suitable for lubricating heavy machinery. The latter is also used as a base for fluids in hydraulic systems.

Illuminants

Cheap illuminants from petroleum have virtually eliminated vegetable oils as burning oils, except in isolated regions. However, candles based on paraffin wax or beeswax need a hardening agent to assist in maintaining their shape in hot weather or to burn without dripping. Next to stearic acid, very highly hydrogenated oils can be used for this purpose.

Other

Stable fats and oils can be used in cosmetics such as, for instance, palm oil or shea nut butter in creams and castor oil in alcohol-based hair dressings. In pharmaceuticals they can be used to carry fatsoluble substances as vitamin concentrates. They can also be used to prevent infestation of crops by insects.

Highly unsaturated oils are used as drying oils in paints and varnishes. Linseed oil is important in this regard, followed by soyabean oil. Castor oil can be chemically dehydrated to give a fast drying oil, suitable for use in water-resistant varnishes and enamels.