Gum arabic (FAO, NWFP 6)
- Extract from : NWFP 6. Coppen J.J.W., 1995. Gums, resins and latexes of plant origin. FAO, Rome. 142 p. (Non-Wood Forest Products, 6). on line
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Contents
DEFINITION
The term gum arabic is used with varying degrees of precision by different groups of people. In the context of its use as a food additive the most recent international specification, published by FAO (FAO, 1990), defines gum arabic as the "dried exudation obtained from the stems and branches of Acacia senegal (L.) Willdenow or closely related species". The specification then proceeds to give limits for certain parameters which have been selected to try and ensure that only gum from Acacia senegal (and closely related species) satisfies the specification (see Quality and prices below). The need for such legislation arises from the need to assure the public on safety grounds that there are no hazards associated with ingestion of gum arabic; gum arabic which complies with the definition and specifications has been tested and shown to be safe to consume.[1]
In Sudan, the term gum arabic is used in a wider context to include two types of gum which are produced and marketed, but which are, nevertheless, clearly separated in both national statistics and trade: "hashab" (from Acacia senegal) and "talha" (from Acacia seyal). In a still wider sense, gum arabic is often taken to mean the gum from any Acacia species (and is sometimes referred to as "Acacia gum"). "Gum arabic" from Zimbabwe, for example, is derived from Acacia karroo.
In practice, therefore, and although most internationally traded gum arabic comes from Acacia senegal, the term "gum arabic" cannot be taken as implying a particular botanical source. In a few cases, so-called gum arabic may not even have been collected from Acacia species, but may originate from Combretum, Albizia or some other genus. In the discussion which follows, the term "gum arabic" will generally be used in the generic sense as any Acacia gum unless it is qualified by some other statement or the botanical source is specified.
Statistical data originating in Sudan and shown in Tables 11a, 11b and 12 separate gum hashab and gum talha. Figures relating to Sudan in other statistical tables (Tables 6, 7, 9 and 10) are assumed to combine both types of gum arabic (hashab and talha).
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- ↑ These specifications are currently (mid-1995) under review by JECFA and it is planned to publish revised ones in 1996.
DESCRIPTION AND USES
Gum arabic from Acacia senegal is a pale to orange-brown coloured solid, which breaks with a glassy fracture. The best grades are in the form of whole, round tears, orange-brown in colour and with a matt surface texture; in the broken, kibbled state the pieces are much paler and have a glassy appearance (see section on quality below). Inferior grades, and gum from species other than Acacia senegal, may not have the characteristic tear shape and are often darker in colour. Gum from Acacia seyal (gum talha) is more friable than the hard tears produced by Acacia senegal and is rarely found as whole lumps in export consignments.
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The gum arabic-yielding Acacias grow in semi-arid areas and the vast majority of gum arabic which enters international trade originates in the so-called gum belt of Sub-Saharan Africa, extending from the northern parts of West Africa eastwards to Sudan and Ethiopia. A little gum is of Indian origin.
Gum arabic is a complex, slightly acidic polysaccharide. The precise chemical and molecular structure differs according to the botanical origin of the gum, and these differences are reflected in some of the analytical properties of the gum. As a result, the functional properties and uses to which gum arabic can be put (and its commercial value) are also very dependent on its origin.
Unlike some other gums such as tragacanth, locust bean and the seaweed gums, gum arabic is very soluble in water and forms solutions over a wide range of concentrations without becoming highly viscous. The combination of high solubility in water and low viscosity confers on gum arabic its highly valued emulsifying, stabilizing, thickening and suspending properties. Despite some substitution of gum arabic by cheaper alternatives, brought about in the past by shortages of supply and high prices, it has remained the most important of the exudate gums and in some applications it has technical advantages which make it difficult to substitute completely. Its uses fall into three main areas: food, pharmaceutical and technical.
Food use
As noted earlier, the FAO specification for gum arabic intended for food use stipulates that it should come from Acacia senegal or closely related species. Even apart from legislative requirements, the quality and technical perfoimance of gum arabic from this source makes it the material of choice in most cases. In Europe, the food additive number of gum arabic is E414.
Confectionery remains a major use for gum arabic, although supply and price pressures have led to a marked reduction in the amount of gum arabic used in some traditional items such as "fruit gums" and pastilles. The role of gum arabic in confectionery products is usually either to prevent crystallization of sugar or to act as an emulsifier. In candy products it is also used as a glaze.
It finds wide application as a means of encapsulating flavours (for example, spray-dried flavours and citrus oils) and is also used in a range of dairy and bakery products (especially as a glaze or topping in the latter). It is used in soft and alcoholic drinks, either as a vehicle for flavouring or as a stabilizer or clouding agent.
Pharmaceutical use
Gum arabic's use in pharmaceuticals is much less than it once was, and it has been displaced in many of its applications by modified starches and celluloses. However, it still finds some use in tablet manufacture, where it functions as a binding agent or as a coating prior to sugar coating, and it is also used as a suspending and emulsifying agent, sometimes in combination with other gums.
Technical and miscellaneous uses
An important non-food/pharmaceutical application of gum arabic is in the printing industry, where it is used to treat offset lithographic plates: as a protective coating to prevent oxidation;
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Tapping Acacia senegal var. Senegal using "sunki", in Sudan. Plantation ca. 12 years old. (Photo: J.J.W. Coppen)
Exudated gum, formed into a pale to orange brown coloured solid, ready for collection. (Photo: The Gum Arabic Co., Ltd., Khartoum)
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Primary cleaning and grading of gum arabic at the Gum Arabic Co. depot, El Obeid, Sudan. (Photo: J.J.W. Coppen)
Final inspection of mechanically cleaned gum arabic at the Gum Arabic Co. export depot, Port Sudan. (Photo: J.J.W. Coppen)
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as a component of solutions to increase hydrophilicity and impart ink repellency to the plates; and as a base for photosensitive chemicals.
Other technical uses include ceramics, where gum arabic helps to strengthen the clay, certain types of inks, and pyrotechnics. Use in textiles, paints and adhesives (including the traditional office glue and postage stamps) has decreased to very low levels in recent years, at least in Western markets.
WORLD SUPPLY AND DEMAND TRENDS
Markets
The use of gum arabic has a very long history but in modern times production and trade has been dominated by Sudan. Levels of supply from Sudan are therefore a good indicator of consumption.
A more detailed discussion of production levels in Sudan is given below, but towards the end of the 1960s total gum arabic production (hashab + talha) was in excess of 60 000 tonnes/year; supplies of gum arabic from other countries meant that total world usage was around 70 000 tonnes. Events in the 1970s and 1980s led to fluctuations in both the supply and price of gum arabic and, as a consequence, to changes in demand. The severe Sahelian drought of 1973/74 resulted in a world shortage of gum arabic and high prices which, in turn, accelerated the replacement of gum arabic by substitutes such as modified starches. A low point of approximately 20 000 tonnes of Sudanese exports was reached in 1975, which recovered to around 40 000 tonnes during 1979. A further drought in 1982-84, combined with political and civil unrest, saw levels of exports fall to below 20 000 tonnes in some years in the mid-/late 1980s and early 1990s.
Demand for gum arabic has therefore been constrained at times by the supply, and under these circumstances end-users who switch to alternatives do not always revert to gum arabic when supply problems are eased. It is unlikely, therefore, that world markets for gum arabic will reach the heights that they once did, although the superior properties of gum arabic (especially good quality material from A. senegal) will ensure that it retains substantial markets if availability is assured and prices are favourable.
The European Community is by far the biggest regional market for gum arabic and imports into it, with sources, are given in Table 6 for the period 1988-93. Imports averaged almost 28 000 tonnes/year over the six years, with a peak of over 32 000 tonnes in 1991.
A breakdown into destinations of imports within the EC is given in Tables 7 and 8 for Sudanese and Nigerian gum arabic, respectively. France and the United Kingdom are the biggest markets (although they both re-export a large proportion of their imports) followed by Italy and Germany. The United Kingdom has been a consistent buyer of Nigerian gum, although France and Germany have imported large quantities in recent years. France is the main importer of gum arabic from the Francophone countries of West and Central Africa.
Outside the EC, the United States is the largest market for gum arabic. Imports for 1991-94, and their sources, are given in Table 9; they averaged 7 500 tonnes annually but exceeded 10 000 tonnes in 1994.
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Japanese imports averaged 1 900 tonnes/year during 1988-94; year-by-yeardetails are shown in Table 10.
Supply sources
The gum belt referred to earlier occurs as a broad band across Sub-Saharan Africa, from Mauritania, Senegal and Mali in the west, through Burkina Faso, Niger, northern parts of Nigeria and Chad to Sudan, Eritrea, Ethiopia and Somalia in the east, and northern parts of Uganda and Kenya. Most of these countries appear in the trade statistics as sources of gum arabic, although they differ greatly in terms of the quantities which are involved.
Sudan is the world's biggest producer of gum arabic, and since very little is consumed domestically it is also the main source of gum in international trade. Sudanese production data are given in Tables 1la and 1lb: 5-year annual averages since 1960 are given in Table lla and yearly figures for the crop years 1988-94 are shown in Table 11b. In bothcases, gum hashab is distinguished from gum talha.
The data in Table 1la show a drop in production by more than half in the last decade compared to that in the 1960s (when it averaged about 48 500 tonnes/year). In the ten years 1950-59 (not shown) production averaged just under 41 000 tonnes/year. The more detailed data in Table llb show an all-time low of 7 600 tonnes in 1992. Since then, production has increased and it is expected to be the highest for some years in 1995.
The proportion of gum talha in Sudanese production of gum arabic (Tables 1la and 11b) is usually around 5-15%. However, in recent years (Table 1 lb) it has varied from less than 200 tonnes (3%) in 1992 to over 11 000 tonnes (33%) in 1994.
Exports from Sudan averaged 20 300 tonnes/year in the period 1988-94 (Table 12). Comparison with production data is difficult because of the uncertainty in the level of carryover of stocks from one year to the next.
Nigeria is the second biggest producer and exporter of gum arabic after Sudan. Direct imports into the European Community from Nigeria averaged 4 500 tormes/year during 1988-93 (Table 6). Import data for the United States (Table 9) show that Nigeria was the second biggest primary source of gum arabic.
Of the other producers, Chad is the next most important after Sudan and Nigeria; direct imports into the EC for 1988-93 averaged 2 000 tonnes/year (Table 6). However, a significant proportion of the gum exported from Chad, as well as from the Central African Republic, is believed to originate in Sudan and enter the neighbouring countries through illegal cross-border trade. Likewise, some gum from Cameroon originates in Chad. The 1 000 tonnes of gum arabic imported into the EC from the former Soviet Union in 1988 represents re-exports of bartered gum from Sudan.
A few countries which have gum-yielding Acacias produce gum for the local market, but not in sufficient quantities to enable exports to be made. Two such examples are Zimbabwe and South Africa, which produce gum arabic from Acacia karroo.
Outside Africa, India produces small amounts of gum, similar in quality to gum talha, but a proportion of her exports of gum arabic consists either of re-exports of African gum or locally produced gum ghatti (from Anogeissus latifolia) misclassified as gum arabic.
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Quality and prices
The quality of gum arabic as received by the importer is very dependent on the source. Gum arabic (hashab) from Sudan is the highest quality and sets the standard by which other "gum arabics" are judged. Not only does Sudanese gum come from a species (Acacia senegal) which intrinsically produces a high quality exudate with superior technical performance, but the collection, cleaning, sorting and handling of it up to the point of export is well organized and highly efficient (see COLLECTION/PRIMARY PROCESSING). Within Sudan, gum arabic from the Kordofan region has the highest reputation, and traders and end-users in importing countries often refer to "Kordofan gum" when indicating their preferences.
Nigerian gum arabic, on the other hand, has a reputation for very variable quality. Some gum is comparable to the best Sudanese quality but much of it is poorer. A major problem for importers and end-users is the inconsistent, and often heterogeneous, nature of the consignments: gum of varying degrees of cleanliness and colour is present, which reflects the less rigorous methods of harvesting and post-harvest treatment practised in Nigeria compared with Sudan. One aspect, in particular, which adversely affects the quality is the mixing of different types of gum, i.e., gum collected from different species of Acacia.
Gum talha from Sudan (produced from Acacia seyal) is intrinsically a poorer quality gum than hashab - it has inferior emulsifying properties and even light-coloured samples of whole gum sometimes form dark solutions in water due to the presence of tannins and other impurities. It is more friable than hashab.
Quality criteria
As noted earlier, an FAO (JECFA) specification exists for gum arabic intended for use as a food additive; in the United States, a Food Chemicals Codex specification exists. For pharmaceutical use, gum arabic appears in many pharmacopoeias, including the British Pharmacopoeia.
The JECFA specification has undergone a number of revisions over the years. The present one (published in 1990) specifies limits on such things as loss on drying, ash, acid-insoluble matter, arsenic, lead and heavy metals. A departure of the present specification from earlier ones (other than a modified definition) is the inclusion of limits on optical rotation and nitrogen content. Their inclusion, and the numerical limits, are designed to ensure that as far as possible only gum from Acacia senegal or closely related species is able to satisfy the requirements (and that, for example, gum talha is excluded).
Although gum arabic intended for pharmaceutical use needs to be of high quality, the BP specification is not as demanding as the JECFA one. Neither optical rotation nor nitrogen content are specified.
Quality control measures in Sudan include a small laboratory at the cleaning and sorting warehouses in Port Sudan. Samples of gum are regularly checked and each export consignment receives a certificate giving analytical data such as moisture content, acidinsoluble matter and optical rotation.
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Grades and prices
There are four main grades of Sudanese gum arabic (hashab), although two of these (HPS and Cleaned) are the main ones to enter international trade. The names of the four grades arise from the way in which the gum is cleaned and sorted. Small amounts of "Natural" gum (i.e., gum which has not been cleaned or sorted) used to be available but there is very little demand for this. In addition, since 1994, a processed grade (kibbled) has been available (see COLLECTION/PRIMARY PROCESSING). The grades and their export prices for 1994/95 (FOB Port Sudan) are as follows: Kibbled US$ 5 000/tonne
| HPS (Hand Picked Selected) | US$ 4 850/tonne |
| Cleaned (or Clear Amber Sorts) | US$ 4 200/tonne |
| Siftings | na |
| Dust | US$ 2 760/tonne |
The prices are set by the organization which controls the whole system of gum arabic production in Sudan, the Gum Arabic Company. They are set just before the start of the tapping season (around September/October) and remain fixed for that year.
Gum talha from Sudan has traditionally only been sold as one grade but from 1995 it is being cleaned and graded to form three grades:
| Super | US$ 950/tonne |
| Standard Clean | US$ 850/tonne |
| Siftings | US$ 400/tonne |
Nigerian gum arabic is sorted into three grades. The top grade (Grade 1) is gum produced from Acacia senegal, and although comparable to Sudanese Cleaned gum it is discounted in price by US$ 400-500/tonne. Grade 2 is gum produced from other species of Acacia (such as Acacia seyal and Acacia sieberana). Grade 3 gum is much darker and very mixed in quality; it may consist of gum from species other than Acacia (such as Combretum and Albizia). Prices in early 1994 (when Sudanese Cleaned gum was US$ 4 000/tonne) were:
| Grade 1 | US$ 3 500/tonne |
| Grade 2 | US$ 600-700/tonne |
| Grade 3 | na |
PLANT SOURCES
Botanical names
Family Leguminosae (Mimosoideae):
Acacia spp., especially:
- Acacia senegal (L.) Willd. (Accepted name: Senegalia senegal).
- Acacia seyal Del. (Accepted name: Vachellia seyal).
Numerous Acacia species yield gum, either by natural exudation or after tapping, but almost all gum arabic of commerce originates either from Acacia senegal or Acacia seyal. There is
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disagreement over some aspects of Acacia taxonomy but Acacia senegal is generally regarded as occurring as four varieties:
- Acacia senegal (L.) Willd. var. senegal (syn. Acacia verek Guill. & Perr.)
- Acacia senegal (L.) Willd. var. kerensis Schweinf.
- Acacia senegal (L.) Willd. var. rostrata Brenan
- Acacia senegal (L.) Willd. var. leiorhachis Brenan (syn. Acacia circummarginata Chiov.)
Acacia seyal occurs as two varieties:
- Acacia seyal Del. var. seyal
- Acacia seyal Del. var. fistula (Schweinf.) Oliv.
Other species of Acacia from which gum is, or has been, collected for local use or as minor components of poorer quality shipments for export include:
- Acacia karroo Hayne (Accepted name: Vachellia karroo).
- Acacia paoli Chiov. (Accepted name: Vachellia paolii).
- Acacia polyacantha Willd. (Accepted name: Senegalia polyacantha).
- Acacia sieberana DC. (Accepted name: Vachellia sieberiana).
Description and distribution
Acacia senegal var. senegal is the most widely distributed of the four varieties of Acacia senegal and the most important and best quality source of gum arabic. It is the only variety found in Sudan, where both natural stands and plantations are tapped. It is a small to medium sized thorny tree, with a stem which is irregular in form and often highly branched. In leaf, like many other Acacias, it has a dense, spreading crown. In common with other members of the Acacia senegal complex it has characteristic sets of prickles on the branches, usually in threes with the middle one hooked downward and the lateral ones curved upward. The bark is not papery or peeling. In Africa it occurs throughout the gum belt described earlier but is also found in the arid or semi-arid areas of Tanzania, Zambia, Zimbabwe and Mozambique. It has a limited occurrence in India and Pakistan.
The other varieties of Acacia senegal have a much more restricted distribution than var. senegal and provide only very tiny amounts of gum to the market. Acacia senegal var. kerensis has a slightly yellowish, sometimes peeling bark and smaller pods than var. senegal. It occurs in parts of Somalia, Uganda, Kenya and Tanzania. Acacia senegal var. leiorhachis is also found in parts of East Africa but it occurs also in Central and Southern Africa (Zambia, Zimbabwe, Botswana and South Africa), In Kenya it occurs in two growth forms: as a well-formed tree with spreading crown and as a "whippy" form in which three or four spindly branches extend upwards and away from the rest of the tree. Acacia senegal var. rostrata is also variable and occurs as a tree with flaking, papery bark or in a more shrubby form. It is mainly confined to parts of Central and Southern Africa.
Acacia seyal var. seyal is the source of gum talha and has a much more extended range than var. fistula. It has a single straight stem with a characteristic, pronounced colour, usually orange-red, to the powdery bark, and straight thorns rather than the curved prickles of Acacia senegal.
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It has a wide distribution in Africa and is found in most of the countries where Acacia senegal occurs; in Sudan it occurs in greater numbers than Acacia senegal. Acacia seyal var. fistula is distinguished from var. seyal by its creamy white bark and the presence of ant galls. It is limited to the eastern half of Africa and is not known to be used as a source of gum.
Gum from Acacia karroo is produced in Zimbabwe and South Africa, although the species has a much wider distribution. It occurs over a wide range of altitudes and in many different habitats. In Ghana, Acacia polyacantha and Acacia sieberana occur in the hotter, drier, northern parts of the country and are occasional sources of gum.
COLLECTION/PRIMARY PROCESSING
In Sudan and Nigeria, virtually all gum from Acacia senegal is obtained by tapping the trees; there is very little natural exudation. The reverse is true with Acacia seyal gum. In countries such as Kenya Acacia senegal does produce gum naturally and all of the gum which is collected comes from harvesting natural exudate.
The following account describes the collection, handling and primary processing (cleaning) of gum hashab - gum arabic from Acacia senegal - in Sudan. Tapping methods have been developed which do not damage the trees, and handling and cleaning practices have been optimized to produce a superior quality product.
Tapping begins when the trees are just starting to shed their leaves, usually about the end of October or beginning of November. After five weeks the first collections of gum are made, with further collections from the same trees at approximately 15-day intervals until the end of February, making five or six collections in total. The older methods of making small incisions into the tree with an axe have largely been replaced by one which utilizes a specially designed tool, a "sunki". This has a metal head fixed to a long wooden handle. The pointed end of the head is pushed tangentially into the stem or branch so as to penetrate just below the bark, and then pulled up so as to strip a small length of bark longitudinally from the wood. Damage to the wood should be minimal. Several branches are treated in a similar manner at one tapping. In following years, other branches or the reverse side of the previously treated branch are tapped.
After this superficial injury, tears of gum form on the exposed surfaces and are left to dry and harden. As far as possible, the tears are picked by hand from the stems and branches where they have formed, and not by knocking to the ground where they can pick up dirt. They are placed in an open basket carried by the collector; the use of plastic sacks has been found to increase the risk of moisture retention and mould formation.
For trees which have been planted from seed, tapping starts at age 4-5 years; for those planted as seedlings, tapping can start in the third year.
In Sudan, the collector sells his gum at regular gum auctions, either to a trader who then sells it on to the Gum Arabic Company, or directly to the Company if they intervene because the price does not reach the guaranteed floor price. Any trader who buys gum then undertakes the process of cleaning and grading it. This is done by hand, usually by women, who sort it into piles of whole tears and smaller pieces, separating any dark gum and removing pieces of bark and other foreign matter.
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The same principles of cleaning and sorting are followed in most other countries and the trader or trading organization then usually exports the graded gum. In Sudan, however, the cleaning process is repeated when the Gum Arabic Company receives consignments of gum from the regional centres at its export warehouses in Port Sudan. Since 1991 the cleaning operation has been mechanized using a system of conveyor belts and shaking and sieving machines. Final inspection of the cleaned gum and removal of any remaining foreign matter or dark coloured pieces is made manually as it moves on a belt to be bagged.
Yields
Yields of gum arabic from individual trees are very variable and little reliable data are available on which to base sound estimates of "average" yields. A figure of 250 g of gum per tree per season is often cited as an average yield. Yields of several kg or more have been reported from individual trees.
In Sudan, yields from cultivated Acacia senegal are said to increase up to the age of 15 years, when they level out and then begin to decline after 20 years. At this stage, if desired, trees can be coppiced and after a suitable period of time (and pruning) tapping can recommence on the new stems. In Mali, the best yields from Acacia senegal are said to be produced between ages seven and 15 years.
VALUE-ADDED PROCESSING
When imported into the consumer countries most gum arabic is further processed into kibbled and powdered forms. Kibbling entails passing whole or large lumps of gum through a hammer mill and then screening it to produce smaller granules of more uniform size. These pieces are more easily dissolved in water, and under more reproducible conditions, than the raw gum and so are preferred by the end-user.
As an extension to its mechanized cleaning process, Sudan recently installed machinery to produce kibbled gum arabic. In so doing, it became the first producer country to gain added value in this way. Production began during the 1993/94 season and approximately 2 500 tonnes of kibbled gum was produced.
Powdered gum may be produced from kibbled gum but it may also be produced by a process known as spray drying. This furnishes a high-quality, free-flowing powder with even better solubility characteristics than kibbled gum. The gum is dissolved in water, filtered and/or centrifuged to remove impurities and the solution, after pasteurization to remove microbial contamination, is sprayed into a stream of hot air to promote evaporation of the water. By altering atomizing conditions, powder can be produced with varying particle sizes and bulk densities, according to the end-user's requirements. Spray drying is an energy-intensive process and this, together with the requirements for large quantities of pure water, makes it something that most gum arabic producers could not consider. The difficulty of handling large volumes of aqueous solutions of gum in a producer country - where ambient temperatures are high - without suffering unacceptable increases in the microbiological load adds further to the problem.
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PRODUCTS OTHER THAN GUM
No other items of trade are produced from the gum-yielding Acacias, although they are used locally as sources of fuelwood. Many species of Acacia are important sources of browse for livestock.
DEVELOPMENTAL POTENTIAL
Acacia senegal has been widely planted in Sudan and some other countries as a means of combating the process of desertification; it has also been used more generally for afforestation of arid tracts and soil reclamation. As well as environmental benefits, Acacia senegal provides socio-economic benefits to many thousands of communities in the "gum belt" through the production of gum arabic. In Sudan, especially, tending the "gum gardens" remains an integral way of life for many people and a valuable source of cash income.
However, demand for gum arabic is such that importers in end-user countries are always keen to encourage new sources of supply to supplement traditional sources. Thus, in recent years, Kenya has emerged as a new supplier of gum arabic to the world market, albeit a tiny one in comparison to most of the established African producers. However, the Kenyan experience is one which could be followed in some other African countries. In the semi-arid areas where Acacia senegal is found, the local people are often pastoralists involved in herding activities. Climatic and ecological conditions are not favourable to agriculture and there are few opportunities for growing cash crops. In these circumstances production of gum arabic - either from an existing, wild resource of a suitable Acacia species or from Acacia senegal planted as part of an agroforestry system - can generate much-needed cash.
A further attraction of promoting gum arabic collection under the conditions described above is that the realization by the local people that an economic value can be placed on the trees is likely to encourage them to preserve the trees and not to cut them down so readily for use as fuelwood as happens at present.
There are therefore numerous benefits to be gained from the production of gum arabic, either through the utilization of natural stands of Acacia or from planted sources, providing it is carried out in a sustainable manner. If due attention is given to the production of high quality gum (in particular, that gum from different Acacia species is not mixed) then not only can a new producing country aim to meet domestic needs, but it should also be capable of entering the export market.
Research needs
Of the gum-yielding Acacias, most research on agronomic aspects has concentrated (justifiably) on Acacia senegal, although further work remains to be done. Chemical analysis and quality assessment has been carried out on gum exudates from a large number of Acacia species (as well as gum arabic-like exudates from other genera), but relatively little detailed information is available on the intra-specific variation of Acacia senegal gum. Some areas requiring further research are therefore:
- Vegetative propagation. Successful development of vegetative methods of propagation of Acacia senegal would enhance selection and breeding programmes aimed at producing superior gum-yielding trees.
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- Chemical screening. In-depth studies need to be carried out to learn more about site-to-site, tree-to-tree and seasonal variations in gum quality. This applies to all gum-yielding Acacias.
- Yield assessment. Trial plots need to be established (in both natural populations and plantations) to measure gum yields on a per tree basis, and to determine the variation between and within sites.
- Resource assessment. There is an urgent need to assess the size and suitability of wild, gum-yielding Acacia resources in those countries where they exist but where there is no, or only minor, gum arabic production.
SELECTED BIBLIOGRAPHY
- ANDERSON, D.M.W. (1993) Some factors influencing the demand for gum arabic (Acacia senegal (L.) Willd.) and other water-soluble tree exudates. Forest Ecology and Management, 58, 1-18.
- ANDERSON, D.M.W., BRIDGEMAN, M.M.E., FARQUHAR, J.G.K. and McNAB, C.G.A. (1983) The chemical characterization of the test article used in toxicological studies of gum arabic (Acacia senegal (L.) Willd.). The International Tree Crops Journal, 2, 245-254.
- ANDERSON, D.M.W., BROWN DOUGLAS, D.M., MORRISON, N.A. and WEIPING, W. (1990) Specifications for gum arabic (Acacia senegal); analytical data for samples collected between 1904 and 1989. Food Additives and Contaminants, 7(3), 303-321.
- ANDERSON, D.M.W., MILLAR, J.R.A. and WEIPING, W. (1991) Gum arabic (Acacia senegal) from Niger - comparison with other sources and potential agroforestry development. Biochemical Systematics and Ecology, 19(6), 447-452.
- ANDERSON, D.M.W. and PINTO, G. (1980) Variations in the composition and properties of the gum exuded by Acacia karroo Hayne in different African locations. Botanical Journal of the Linnean Society, 80(1), 85-89.
- ANDERSON, D.M.W. and WEIPING, W. (1991) Acacia seyal and Acacia sieberana - sources of commercial gum talha in Niger and Uganda. The International Tree Crops Journal, 7(1/2), 29-40.
- AWOUDA, El-H.M. (1988) Outlook for gum arabic production and supply. pp 425-434. In Gums and Stabilisers for the Food Industry, Vol. 4. Proceedings of 4th International Conference, Wrexham, July, 1987. Oxford: IRL Press.
- AWOUDA, El-H.M. (1990) Indicators for present and future supply of gum arabic. pp 45-54. In Gums and Stabilisers for the Food Industry, Vol. 5. Proceedings of 5th International Conference, Wrexham, July, 1989. Oxford: IRL Press.
- BADI, K.H., AHMED, A.E.H. and BAYOUMI, A.A.M.S. (1989) The Forests of Sudan. 184 pp. Khartoum: Ministry of Agriculture, Department of Forestry.
- BARBIER, E.B. (1992) Rehabilitating gum arabic systems in Sudan: economic and environmental implications. Environmental and Resource Economics, 2(4), 341-358.
- BESHAI A.A. (1984) The economics of a primary commodity: gum arabic. Oxford Bulletin of Economics and Statistics, 46(4), 371-381.
[24]
- BHATT, J.R. and RAM, H.Y.M. (1990) Ethephon-induced gum production in Acacia senegal and its potential value in the semi-arid regions of India. Current Science, 59(23), 1247-1250.
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- BP (1993) Acacia. pp 19-20. In British Pharmacopoeia, Vol. 1. London: Her Majesty's Stationery Office.
- DIONE, M. and VASSAL, J. (1993) [Experimental study on the means of production of gum trees of Acacia senegal: looking back on the gum tree development programmes in the Senegalese Sahel] (in French). pp 22-41. In Proceedings of 5th Sahel Workshop Natural Resources and Social Conflicts in the Sahel, 4-6 January, 1993. Aarhus, Denmark: Aarhus University Press.
- DSS (1993) Gum Arabic. A Potential Source of Income for the Muko godo Community? [in Kenya]. Report by Department of Social Services. 14 pp. Nairobi: Ministry of Culture and Social Services.
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[26]
| 1988 | 1989 | 1990 | 1991 | 1992 | 1993 | |
|---|---|---|---|---|---|---|
| Total | 23797 | 26151 | 27630 | 32102 | 29963 | 26500 |
| Of which from: | ||||||
| Sudan | 9963 | 12463 | 14400 | 17098 | 10215 | 9304 |
| Nigeria | 3471 | 3538 | 4385 | 3568 | 7243 | 4759 |
| France | 1876 | 2365 | 1993 | 2104 | 3003 | 2624 |
| UK | 2293 | 1373 | 1698 | 1855 | 2512 | 1746 |
| Chad | 1443 | 1469 | 1059 | 2153 | 2422 | 3527 |
| Germany | 726 | 838 | 670 | 997 | 1353 | 1177 |
| Senegal | 716 | 301 | 276 | 273 | 245 | 449 |
| Cameroon | 344 | 345 | 302 | 75 | 573 | 841 |
| India | 121 | 452 | 587 | 435 | 469 | 369 |
| USA | 439 | 355 | 432 | 978 | 316 | 163 |
| Netherlands | 75 | 138 | 1043 | 1296 | 184 | 87 |
| Mauritania | 200 | 595 | - | 32 | 48 | 55 |
| Mali | 187 | 391 | 69 | 75 | 32 | 77 |
| Tanzania | 88 | 31 | 27 | 118 | 160 | 176 |
| Ethiopia | 74 | 256 | 68 | 20 | 43 | 27 |
| Somalia | 24 | 21 | 82 | 38 | 49 | 1 |
| Niger | 41 | 60 | - | 20 | 155 | 169 |
| Central African Republic | 74 | 72 | - | 74 | 79 | 33 |
| Ghana | 93 | 212 | - | - | - | - |
| Kenya | - | - | - | 18 | 121 | 102 |
| Soviet Union, former | 1077 | - | - | - | 20 | - |
Source: Eurostat
[27]
| 1988 | 1989 | 1990 | 1991 | 1992 | 1993 | |
|---|---|---|---|---|---|---|
| Total | 9963 | 12463 | 14400 | 17098 | 10215 | 9304 |
| Of which to: | ||||||
| France | 3016 | 3815 | 5023 | 7074 | 5219 | 5118 |
| UK | 2580 | 3176 | 3053 | 2521 | 2118 | 1168 |
| Italy | 2205 | 2645 | 2675 | 3431 | 1007 | 1935 |
| Germany | 1265 | 1659 | 1388 | 1804 | 1027 | 478 |
| Denmark | 441 | 716 | 755 | 727 | 608 | 440 |
| Belgium/Luxembourg | 261 | 200 | 360 | 280 | 80 | 120 |
| Spain | 129 | 159 | 96 | 90 | 56 | 45 |
| Greece | 65 | 90 | 50 | 31 | - | - |
| Netherlands | - | - | 1000 | 1140 | 100 | - |
| Portugal | 1 | 3 | - | - | - | - |
| Ireland | - | - | - | - | - | - |
Source: Eurostat
| 1988 | 1989 | 1990 | 1991 | 1992 | 1993 | |
|---|---|---|---|---|---|---|
| Total | 3471 | 3538 | 4385 | 3568 | 7243 | 4759 |
| Of which to: | ||||||
| France | 437 | 437 | 403 | 167 | 1256 | 1152 |
| UK | 1982 | 2204 | 2862 | 2411 | 3244 | 2315 |
| Italy | 2 | - | - | - | - | 38 |
| Germany | 974 | 873 | 1119 | 990 | 2734 | 1237 |
| Denmark | 54 | - | - | - | - | - |
| Belgium/Luxembourg | - | - | - | - | - | 12 |
| Spain | 12 | 14 | 1 | - | - | - |
| Greece | - | 10 | - | - | 2 | - |
| Netherlands | 10 | - | - | - | 7 | 5 |
| Portugal | - | - | - | - | - | - |
| Ireland | - | - | - | - | - | - |
Source: Eurostat
[28]
| 1991 | 1992 | 1993 | 1994 | |||
|---|---|---|---|---|---|---|
| Total | 8313 | 5802 | 5508 | 10434 | ||
| Of which from: | ||||||
| Sudan | 5480 | 2471 | 1800 | 5367 | ||
| France | 2511 | 2430 | 2699 | 2951 | ||
| UK | 278 | 678 | 740 | 524 | ||
| Nigeria | - | 143 | 81 | 1061 | ||
| Chad | - | 18 | 60 | 342 | ||
| India | - | 18 | 2 | 102 | ||
| Germany | 2 | 12 | 5 | 22 | ||
| Egypt | 35 | 10 | - | - | ||
| Kenya | - | - | 80 | 34 | ||
| Western Sahara | - | 20 | - | - | ||
| Somalia | - | - | 4 | - | ||
| Djibouti | - | - | - | 7 | ||
Source: National statistics
| 1988 | 1989 | 1990 | 1991 | 1992 | 1993 | 1994 | |
|---|---|---|---|---|---|---|---|
| Total | 1656 | 1821 | 2735 | 2022 | 2019 | 1219 | 1804 |
| Of which from: | |||||||
| Sudan | 1606 | 1791 | 2702 | 1983 | 1644 | 741 | 1447 |
| France | 16 | 10 | 20 | 12 | 60 | 145 | 200 |
| UK | 6 | 8 | 8 | 20 | 176 | 245 | 110 |
| USA | 28 | 12 | 5 | 7 | 62 | 43 | 38 |
| Nigeria | - | - | - | - | - | 20 | - |
| Guinea Bissau | - | - | - | - | 20 | - | - |
| Kenya | - | - | - | - | 12 | - | - |
| India | - | - | - | - | - | 20 | - |
Source: National statistics
[29]
| 1960-64 | 1965-69 | 1970-74 | 1975-79 | 1980-84 | 1985-89 | 1990-94 | |
|---|---|---|---|---|---|---|---|
| Annual average | 46550 | 50576 | 35073 | 37408 | 31079 | 23721 | 18358 |
| Of which: | |||||||
| Gum hashab | 44299 | 47434 | 30910 | 36026 | 26721 | 19777 | 15038 |
| Gum talha | 2251 | 3142 | 4163 | 1382 | 4358 | 3944 | 3320 |
Source: Gum Arabic Company, Sudan
| 1988 | 1989 | 1990 | 1991 | 1992 | 1993 | 1994 | |
|---|---|---|---|---|---|---|---|
| Total | 26000 | 28948 | 25733 | 12351 | 7616 | 12865 | 33227 |
| Of which: | |||||||
| Gum hashab | 20000 | 24256 | 22408 | 11756 | 7439 | 11410 | 22178 |
| Gum talha | 6000 | 4692 | 3325 | 595 | 177 | 1455 | 11049 |
Source: Gum Arabic Company, Sudan
| 1988 | 1989 | 1990 | 1991 | 1992 | 1993 | 1994 | |
|---|---|---|---|---|---|---|---|
| Total | 18603 | 19352 | 26912 | 24978 | 14068 | 15730 | 22735 |
| Of which: | |||||||
| Gum hashab | 16672 | 17385 | 22960 | 21543 | 8198 | 9925 | 18339 |
| Gum talha | 1931 | 1967 | 3952 | 3435 | 5870 | 5805 | 4396 |
Source: Gum Arabic Company, Sudan
