Historically Acacia Seyal gums in the Sudan is ranking as a second important gum product after A. senegal in terms of quantities 10% in average until 2011. Thus the contribution percentages within the last four years (2012-2015) jumped to almost 60% in average. A. seyal trees coverage extend in an area of 36,000 square kilometers (3.6 million ha) in a latitude ranging between 10 to 140North. The distribution of the A.seyal stand is extensively on the clay soil plains where an average rainfall is ranging between 300 to 400 mm. Two infraspecific variants of A. seyal widely distributed in Sudan separated on the basis of the presence and absence of the ant-galls and the colour of the bark. Ant-gall and white colored bark are the characteristics of variety fistula, while the bark of variety of seyal is green or red. Despite the significant contribution of A. seyal in the exports market in the Sudan, farmers have slightly a poor knowledge of post-harvest cultural practices of A. seyal of which proper methods of storage conditions and gum stacking. Nevertheless, this paper is trying to review the existing research in the areas of pre- and post-harvest cultural practices including tree husbandry, tapping, gum collection, handling and storage. Exudation mechanisms (tapping and natural exudation) are also been highlighted coupled with physical and chemical properties of A. seyal (characterization) as well as moisture content, colour, tannins etc., aiming at establishing a clear protocol of the A. seyal tree in the Sudan.
Acacia Gum is a natural agricultural resource from the Gum Belt region of Africa, i.e. countries geographically ranging from East to West -from Sudan, Somalia, Eritrea and Ethiopia to Chad, Central African Republic, Mali, Niger and further west up to Nigeria, Senegal and even Mauritania. Economically speaking, Acacia Gum mainly comes from Sudan, Chad and Nigeria.
In Sudan, the most important NWFPs (Non-Wood Forest Products) is Gum Arabic, which exudates from Acacia senegal known as hashab or hard gum and Acacia seyal known as Talh or friable gum. Both species spread naturally in the central belt of the low rainfall savannah where they existed in pure or mixed stands, in the clay plains in the East and sandy soils in the West [].
Despite the significant contribution of A. seyal in the exports market in the Sudan, farmers have slightly a poor knowledge of post-harvest cultural practices of A. seyal of which proper methods of storage conditions and gum stacking. Nevertheless, this paper is trying to review the existing research in the areas of pre- and post-harvest cultural practices including tree husbandry, tapping, gum collection, handling and storage. Physical and chemical properties of A. seyal (characterization) aiming at establishing a clear protocol of the seyal tree in the Sudan.
Acacia seyal trees are up to 17 m tall in Sudan, with a flat top crown. It has a distinctive smooth powdery bark, from white to greenish yellow or orange red, with a green layer beneath. In some population both red and yellow barked trees can be found. There are two varieties, differing primarily in whether or not pseudo-galls (“ant galls”) develop and in bark colour. In A. seyal var. seyal, there are no pseudo-galls and a reddish bark color prevails, although periodic bark exfoliation exposes a pale powdery surface which darkens slowly. In A. seyalvar. fistula pseudo-galls are present and the powdery bark typically remains whitish or greenish-yellow.
In general, there are two main varieties of A. seyal; variety seyal and variety fistula. Variety seyal is found in both western and eastern Africa and also on the Arabian Peninsula, whilevariety fistula is found in the eastern parts of Africa indicate that variety seyal is native to northern-tropical Africa and Egypt. The two varieties can be easily distinguished; variety seyal has a greenish-yellow to reddish-brown bark, while variety fistula has white to greenish-yellow bark. Figure (1) shows the distribution of A. seyal varieties with respect to rainfall. However, A. seyal trees are naturally grown in the Sudan till yet no reforestation done by human been [].
Fig. Distribution of Acacia seyal varieties in Africa, with respect to rainfall
. M. H. Mohammed, Management of Natural Stands of Acacia seyal Del. variety seyal (Brenan) for Production of Gum Talha, South Kordofan, Sudan, MSc. Thesis in Forestry, University of Khartoum (2011).
Most of the farmers in the sand plains areas have adequate awareness of pre-harvest cultural practices for A. senegal. This awareness is due to their vast indigenous knowledge on the traditional farming system additional to the extensive extension held by the Forest National Cooperation (FNC) as a result of a comprehensive research done in the last five decades. The comprehensive research comes up with a clear protocol for a tree husbandry, taping of tree as well as proper way of collecting gums (Abdel Nour ., 1889). However, farmers have slightly a poor knowledge of post-harvest cultural practices of A. seyalof which proper methods of storage conditions and gum stacking. Nevertheless, sufficient research has been done in these fields (Osman, 2002).For instant, a protocol for a tree of A. seyal is not yet been established coupled with poor indigenous knowledge of the local farmers in the clay plains regarding tree husbandry, taping and gum collection. The results of that are inferior quality and poor nodules physical characteristics .
Collectors harvest the partially dried gum, and multiple collections up to three times at three-week intervals from the same tree are possible. A yield of 300-7000 g is obtained per tree annually. On the other hand, A. seyal is generally collected from natural exudation without tapping. In certain gum sources the natural exudates were noted as being darker in colour compared to gums obtained by tapping (Anderson & Bridgeman, 1985). The method of gum production might be one of the factors causing the difference of colour between A. senegaland A. seyal. Recently, Fadl and Gebauer reported that the middle stem tapping caused highest A. seyal gum exudation. A. seyal gum production by tapping might be increased in the future if the problem such as serious stress to the tree is avoided . Tapping is often done by using traditional tools such as axe, Mohfar, Sonki and Makmak shown in figure . Using Makmak is highly recommended. Fadl reported that Makmak was the best tool for tapping A. seyal. The reason can be seen in the wide edge on the top of the tool, which allows better removal of the bark.
Fig; Shows Makmak, axe, mohfar, and sonkey (from left to right). Source: Fadl and
Chemical and physical properties of gum are considered as important characters for the article of commerce, to ensure the identity and purity of gum and avoiding mixing and adulteration. Moisture content gives an indicator for both purity and a real weight. All results fall within limit specified by JECFA (1990).
The Specific Optical Rotation (S.O.R.) the range of the mean value vary from (+ 51.4 ˚) to (+ 62.8˚).
The range of the mean value of Protein content vary from 0.69 to 0.96 %.The pH ranged from 4.02 to 4.77 for Acacia seyal.
Table : The physicochemical properties of Acacia seyal species (Obied, 2012)
Acacia Seyal Gums in Sudan: A review
 Department of Chemical Engineering, Faculty of Engineering, University of Khartoum
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 Kenana Sugar Company limited, Strategic Planning,( Email: firstname.lastname@example.org )
 University of Kordofan( Email: email@example.com )
Arabic (saffar abiad, soffa,suffar abyad, talh, suffer abiad, suffar ahmer);
English (shittim wood, white-galled acacia, whistling thorn, white thorn, white whistling thorn);
French (epineux, mimosa, seyal); Fula (bulki);
Hausa (dushe kerafi);
Tigrigna (Tseada chea, qeyehchea, keih chea);
Trade name (gum talha, shittimwood) .
Acacia seyal is a small to medium-sized tree, growing to 17 m tall and 60 cm in diameter at breast height; crown is umbrella shaped, resembling that of A. tortilis. A characteristic feature of the tree is its rust-coloured powdery bark; A. seyal var. fistula has whitish bark. Large, straight spines occur on the branches, and smaller, curved thorns are present near the tips of the branches. Leaves bipinnate, dark green, 4-12 pairs of pinnae, 10-12 pairs of leaflets each 1-2 x 4-12 mm. Flowers clustered in shining, yellow, globose heads, 1.5 cm diameter, on stems 3 cm long. Pods 10-15 x 1 cm, slightly curved, light brown when mature and indehiscent, containing 6-10 seeds. Seeds are elliptic (5-6 x 2.5-3.5 mm ), olive-brown branches.
The generic name ‘acacia’ comes from the Greek word ‘akis’, meaning ‘point’ or ‘barb’.
Bees are the likely pollinators. Flowers are borne in profusion and are spicy scented or sweet smelling. The seeds of A. s. var. seyal are locally dispersed in large amounts and have been found deposited in animal feces along transhumance routes. No dispersal mechanism has been located for A. seyal var. fistula. Flowering is concentrated in the middle of the dry season, with ripe fruits appearing 4 months later.
Seyal occurs from Senegal to the Red Sea and in Arabia. It is common in many other parts of Africa, especially north of the equator, from 10 to 12 degrees. It also occurs in east and southern Africa. In the southern and western Sudan, it is one of the most common trees in the savannah and often occurs as a pure forest over quite large areas of country. Frequently, it grows in groups or patches, sometimes of considerable size, in areas inhabited by A. senegal. This species is characteristic of the Nile region. It is tolerant to high pH (6-8), salts and periodic flooding. Acacia seyal var. fistula is more tolerant to waterlogging than A. seyal var. seyal.
Altitude: 1700-2000 m,
Mean annual temperature: 18-28 deg. C
Mean annual rainfall: 250-1000 mm
Soil type: It normally prefers heavy, clayey soils, stony gravely alluvial soils or humic soils.
Egypt, Eritrea, Ethiopia, Ghana, Iran, Israel, Kenya, Malawi, Mali, Mozambique, Namibia, Niger, Nigeria, Saudi Arabia, Senegal, Sudan, Syrian Arab Republic, Tanzania, Uganda, Yemen, Republic of, Zambia, Zimbabwe .
Afghanistan, Bangladesh, Bhutan, India, Nepal, Portugal, Sri Lanka, US The map above shows countries where the species has been planted. It does neither suggest that the species can be planted in every ecological zone within that country, nor that the species can not be planted in other countries than those depicted. Since some tree species are invasive, you need to follow biosafety procedures that apply to your planting site .
Gum talha from A. seyal is eaten when fresh, although it has slightly acid taste. It is also mixed with pulp from the fruit of Balanites aegyptiaca to make a syrup.
The bark is extensively used for feeding cattle, sheep and goats during the dry season. When fresh, it is smooth and relatively soft. In February to March (the dry season in Kenya) thick branches are lopped and animals browse the bark and eat the leaves, which are relatively few at that time. The pods and leaves are nutritious and palatable to livestock. The feed value crude protein content is 11-15 % in leaves and 15-24 % in fruits. Digestible protein is 8-12 % in leaves and 13-15 % in fruits, which have a high digestibility. Leaves, pods and flowers are a major source of early dry-season fodder for sheep and goats over much of Africa. A. seyal is considered the best fodder plantin northern Nigeria and the Sahelian savannah. In the dry season in western Sudan, the Fulani drive their cattle to the districts where it grows. Branches (sometimes even the entire crown) are lopped in times of fodder scarcity.
Its yellow fragrant flowers yield a white-coloured honey with mild aroma.
A. seyal produces good, dense firewood that is used widely throughout its range. The smoke is pleasantly fragrant and the wood burns rather quickly. In Chad the tree is considered to provide the best fuelwood. In Sudan it is used to make a fragrant fire over which women perfume themselves. A. seyal var. seyal is an important source of rural energy as both firewood and charcoal. Trees managed on a 10-15 years rotation yield 10-35 cubic m/ha of fuelwood a year.
Roots are used for making staves. The bark of A. seyal is used for making rope. The fibre has promising technological characteristics for use as particleboard.
The wood is pale yellow to medium brown, with localized pinkish-brown patches and some dark mahogany-red heartwood in larger or older individuals. A. seyal wood has potential in rural areas as timber. If the tree is grown with few knots and straight grain, sprayed with insecticide after felling, and treated with preservatives, the timber works well and is hard and tough. It produces a hard, dark wood, called shittim wood, with interlocked, irregular and coarsetextured grain. It takes good a polish but is susceptible to insect attack. Therefore, it must be properly treated by splitting it, putting it under water for a few weeks and then drying it thoroughly. Shittim wood was used by ancient Egyptians for pharaohs’ coffins.
Gum or resin
A. seyal gum (talha gum) is darker and inferior in quality to that of A. senegal (gum arabic). However, it forms 10% of the Sudanese gum exported to India and Europe. The gum is edible when fresh, with a slightly acidic taste. Talha does not meet the requirements of the food industry because it has not been toxicologically evaluated and contains tannins. For technological use outside the food industry, talha gum is attractive because of its clarity and solubility.
Tannin or dyestuff
Pods and bark contain 20% tannin. Gum is mixed with soot and powdered Nubian sandstone for black and red ink. The bark contains 18-30 % tannins and is a source of red dye.
The smoke produced by burning the wood of A. seyal acts as a fumigant against insects and lice. Chemicals in the bark of A. seyal kill the freshwater snails that carry bilharzia parasites and algae growing in ponds. Methanolic extracts from the bark of A. seyal applied to ponds display agricidal properties. Molluscidal properties have been demonstrated with spray-dried powder of ethyl extracts, which are effective against schistomiasis vectors Biomphalaria pfeifferi and Bulinus truncatus.
The bark, leaves and gums are used for colds, diarrhoea, hemorrhage, jaundice, headache and burns. A bark decoction is used against leprosy and dysentery, is a stimulant and acts as a purgative for humans and animals. Exposure to smoke is believed to relieve rheumatic pains. A root decoction mixed with leaves of Combretum glutinosum and curdled milk causes strong diuresis.
Shade or shelter
Where it grows, A. seyal offers shade to livestock in the dry season.
Boundary or barrier or support
In many areas, farmers cut branches of A. seyal to make fences. The thorny branches are good for this purpose and last about 2 years.
The trees are cut at the age of 8-15 years, depending on population pressure and demand for wood. Sometimes the stem is cut at 1.5-2 m above the ground, and a new canopy develops. Pruning of small branches gives better forage yield than lopping of large branches. Evaluation of the response to lopping and cutting of A. seyal var. seyal indicates limited recovery capacity in mature trees. Beating branches to detach leaves and fruits without damaging the axially buds is therefore preferred over lopping to best use these trees as dry season resources.
Seed storage behaviour is orthodox. Viability can be maintained for several years in hermetic storage at 10 deg. C. with 4.5-9% mc. There are 20 000-22 000 seeds/kg.
Over 40 species of insects are reported associated with A. seyal. The bostrychid (Sinoxylon senegalense) is the most notorious in swiftly locating and infesting freshly cut wood especially if lying on the ground. Removal of the bark and stacking cut stems upright minimizes infestation. Treat wood using creosote to prolong durability.