Acacia Seyal

    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 [[1]].

    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.

[1]. H. E. ElKhawad, Gum Arabic Processing and Marketing in the Sudan, MSc. thesis in Chemical Engineering, University of Khartoum, (2008).

   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 [[1]].

                                                                     Fig. Distribution of Acacia seyal varieties in Africa, with respect to rainfall

 [1]. 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 [5]. 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

                                                                                                                     Gebauer 2004

    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)

REFERENCES

Acacia Seyal Gums in Sudan: A review

Sara, S. Awad[1]; Ali, A. Rabah[2]; Hassan, I. Ali[3], Tarig, E. Mahmoud[4]

[1] Industrial Research and Consultancy Center ( E-mail: sara_awad77@hotmail.com )

[2] Department of Chemical Engineering, Faculty of Engineering, University of Khartoum

  ( Email: rabahss@hotmail.com )

[3] Kenana Sugar Company limited, Strategic Planning,( Email: hassan.mofadel@kenana.com )

[4] University of Kordofan( Email: tarigcom@gmail.com )

Amharic (wachu);

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);

Luganda (kasana);

Somali (larai,fullai,jikh);

Swahili (mgunga);

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.

BIOPHYSICAL LIMITS

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.

Native:

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 .

Exotic:

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 .

       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.