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PRODUCTION, MARKETS AND QUALITY CONTROL OF GUM ARABIC IN AFRICA: FINDINGS AND RECOMMENDATIONS FROM AN FAO PROJECT

BEN CHIKAMAI,
Kenya Forestry Research Institute,
P.O. Box 30241,
Nairobi, Kenya.

Introduction

With a view to identifying ways in which production, and more particularly quality, can be increased or improved, all aspects of production, marketing and quality control were reviewed in 12 producing African countries, comprising six Anglophone and six Francophone countries in a project formulated by FAO. The Anglophone countries were Ethiopia, Ghana, Kenya, Nigeria, Sudan and Zimbabwe, while the six Francophone countries were Burkina Faso, Mali, Mauritania, Niger, Senegal and Chad. The findings and the recommendations of this project are summarised in the present paper. The report established that a total of 17 species of Acacia produce gum which is collected by local communities either for domestic use or export. Out of these, four species produce gum that is marketed as gum arabic: Acacia. senegal and A. seyal (across the Sahel) and A. polyacantha and A. karoo (in localized regions). It was further established that whereas the botanical source affects quality of gum arabic, the main factor relates to harvesting and post harvest treatment. Included in this are the method of harvesting, cleaning, sorting and grading practices. Regarding quality control, it was observed that two factors were responsible; lack of a clear definition for gum arabic and inadequate analytical procedures which do not adequately take into account natural product variability. Based on the above considerations, several recommendations were developed as a means of improving production and quality of commercially produced gum arabic.

Background

The project on production, markets and quality control of gum arabic was formulated by FAO with two main objectives:

The project was implemented by a multi-disciplinary team of experts which comprised a three-man international team and an FAO team member. The latter was assisted by a marketing expert and six national consultants. A total of 12 producing African countries were covered comprising six Anglophone and six Francophone countries. The six Anglophone countries were Ethiopia, Ghana, Kenya, Nigeria, Sudan and Zimbabwe, while the six Francophone countries were Burkina Faso, Mali, Mauritania, Niger, Senegal and Chad. The Anglophone countries were covered by the International team while the Francophone countries were covered by the FAO team member and his group. Gum chemistry was carried out by the mission chemist assisted by the FAO team member and one other expert. The project was carried out between April 1995 and December 1996 and covered two gum production seasons allowing for collection of more samples and other data not collected during the first mission. Findings and recommendations of the project are summarised in the present paper.

Mission Findings

Botanical Sources and Management Aspects

Seventeen species were identified as sources of Acacia gum collected by the local communities - either for domestic use or for export (Table 1). Acacia senegal, A. seyal and A. polycantha have widespread distribution within the gum belt. Acacia senegal and A. seyal are variable species with the former having about four varieties while the latter has two. Other species have limited regional distribution. For instance, A. Karoo is confined to Southern Africa (where it is widely distributed), A. drepanolobium and A. Paoli to Eastern Africa and the Horn of Africa, while A. late and A. dudgeoni are confined to West Africa. Acacia gourmaensis, A. macrostachya and A. macrothyrsa have even more restricted distribution in West Africa. Except for Sudan, and to some extent Nigeria, Chad, Mali and Senegal, where initiatives have been undertaken to introduce plantations of A. senegal, the bulk of gum arabic and Acacia gum is derived from natural stands and by natural exudation. In most of the countries, the extent of distribution is not known very precisely, making it difficult to establish the potential for production and for sound management decisions to be taken. The problem in some countries is compounded by a lack of knowledge about the botanical sources and sound practices of gum production and this can lead to inadvertent mixing of gums.

Production, Quality and Markets

Production levels for gum arabic in the 12 countries are shown in Table 2. There is wide variation in the scale of production with Sudan, Nigeria and Chad accounting for the majority of gum arabic in world trade.

Quality of gum arabic was observed to be influenced by two factors, one of which was botanical origin. Gum from different species (A. senegal and A. seyal) exhibited characteristics that were intrinsically different. Even within the same species, different varieties produce gum with different characteristics. Recognising these differences in the species and/or varieties is important in producing gum arabic for desired end use. Besides botanical source, quality is also affected by harvest and post-harvest treatment. Tapping for example, gives a more consistent and better formed gum than collection caused by insect borers. Better quality gum is obtained by picking it off the tree rather than letting it fall on the ground. Above all, mixing the gum from different species at collection time or at post-harvest handling stage results in variability and is the prime reason for poor quality.

Characterisation and specification of gum arabic

The average values (physico-chemical, carbohydrate and amino acid composition) for gum from A.senegal and A. seyal were consistent with published data and typical of each type of gum irrespective of source, i.e., country or locality. However, though related (possessing the same chemical species), the two gums could be distinguished from each other by all the three methods. This supports the idea of producing and marketing the two gums separately if future improvements in quality and quality control are to be attained. It was shown further that A. late and A. polycantha are closely related to A. senegal while A. karoo is closely related to A. seyal.

Meanwhile, within a given type of gum there was significant sample variation brought about either by differences in varieties, climatic factors or handling aspect. These observed variabilities are worth noting and may require applying more than one analytical method before a decision is made when specifying gum arabic for commerce.

Evaluation of the methods revealed that chemometrics when applied to the analytical data obtained in the investigation is a powerful method of characterising the gum arabic of commerce, by identifying individual species of Acacia and those gums which would be adulterants within the terms of the JECFA definition of gum arabic. Acacia. senegal and A. seyal could be separated into distinct clusters, despite the fact that the two are related (Fig. 1).

Table 1:  Source of Acacia gum in twelve African countries covered in the project

Country Acacias utilised for commercial
AG production

Source of

bulk AG produced

Methods of

obtaining AG

 

1

2

Species

3

4

Burkina Faso A. senegal
A. laeta
A. seyal
A. gourmaensis
A. dudgeoni
A.raddiana

**

**
**
**
**
**
**

A. senegal
A. laeta
A. seyal
A. gourmaensis
A. dudgeoni
A.raddiana
 

**
**
**
**
**
**

Mali A. senegal
A. laeta
A. seyal
A. polyacantha
A. raddiana

**
**

**
**
**
**
**

A. senegal
A. laeta
A. seyal
A. polyacantha
A. raddiana

**
**

**
**
**
**
**

Mauritania A. senegal
A. laeta
A. seyal
A. macrostachya

**

**
**
**
**

A. senegal
A. laeta
A. seyal
A. macrostachya

**

**
**
**
**

Senegal A. senegal
A. ehrenbergiana
A. laeta
A. macrostachya
A. macrothyrsa
A. nilitica
A. polycanthat
A. sieberana
A. tortilis

**

**
**
**
**
**
**
**
**
**

A. senegal
A. ehrenbergiana
A. laeta
A. macrostachya
A. macrothyrsa
A. nilitica
A. polycanthat
A. sieberana
A. tortilis

**
**

**
**
**
**
**
**
**
**
**

Sudan A. senegal var.
senegal
A. seyal
var. seyal

**

**

**

A. senegal var.
senegal
A. seyal
var. seyal

**



**

Ethiopia A. senegal var.
senegal
A. senegal
var.
kerensis
A. seyal
var. seyal
A. seyal
var. fistula
A. polyacanthat
A. drepanolobium

**

**

**

**
**
**
**

A. senegal var.
senegal
A. senegal
var.
kerensis
A. seyal
var. seyal
A. seyal
var. fistula
A. polyacantha
A. drepanolobium

**

**

**

**
**
**
**

Kenya A. senegal var.
kerensis
A. paoli
 

**

**

A. senegal var.
kerensis
A. paoli
 

**

**

Zimbabwe A. karroo  

**

A. karroo

**

**

Nigeria A. senegal var.
senegal
A. seyal
var. seyal
A. nilotica
 

**

**
**

A. senegal var.
senegal
A. seyal
var. seyal
A. nilotica

**

**

**
**

Ghana A. sieberana
A. polyacantha
 

**
**

A. sieberana
A. polyacantha
 

**
**

Chad A. senegal var.
senegal
A. laeta
A. seyal
A. polycantha
 

**

**
**
**

A. senegal var.
senegal
A. laeta
A. seyal
A. polycantha

**

**

**

**
**
**

Niger A. senegal
A. seyal
A. raddiana
A. tortilis
A. polyacanthat

**

**
**
**
**
**

A. senegal
A. seyal
A. raddiana
A. tortilis
A. polyacanthat

**

**
**

**
**

1. Plantations        2. Natural Stands                3. Tapping                 4. Natural exudation or incidental injury

 

Table 2: Summary of gum arabic data for 12 African countries (botanical source, production, imports into EC, USA, Japan and main European markets)

Country Main botanic source Annual productiona Annual imports to EC, USA, Japanb Annual imports to main European markets
Sudan A. senegal var.
senegal
A. seyal
17,100

3,900
EC
USA
Japan
12,200
3,800
1,750
France
UK
Italy
Germany
4,900
2,400
2,300
1,300
Nigeria A. senegal var. senegal
A. seyal
60,000-10,000? EC
USA
Japan
4,500
300
3
UK
Germany
France
2,500
1,300
650
Ethiopia A. senegal
A. seyal
250-300
50-100
EC
USA
Japan
80
-
-
Germany 80
Kenya A. senegal var.kerensis}
A. senegal var. senegal}
200-500? EC
USA
Japan
40
30
2
Italy
UK
25
10
Zimbabwe A.karroo <30 EC
USA
Japan
-
-
-
   
Ghana A. polyacantha <10 EC
USA
Japan
50
-
-
UK 50
Burkina Faso A. senegal
A. seyal
200-300        
Chad A. senegal
A. seyal
3,500
1,500
EC 3,500 France
UK
2,800
600
Mali A. senegal
A. seyal
500 EC 140 France 45
Mauritania A. senegal 400 EC 180    
Niger A. senegal
A. seyal
300 EC 150 France 115
Senegal A. senegal 700 EC 450 Fance
UK
300
130

Notes:   a  Estimates except for Sudan which are 7- year annual averages (1988 - 94)
             b  Annual averages from trade statistics (EC and Japan 1988-93; USA 1991-94)

 

Recommendations

Production, Quality and Markets

Education, training and dissemination of information were identified as key to improving production, its quality and the prospects for developing new or increased markets.

It was therefore recommended that:

The first step should be a regional workshop to sensitise both the producer and consumer countries on the initiatives already undertaken by FAO in relation to promoting the importance and value of gum arabic, including regional corporation. This could be followed by carefully structured study tours in Sudan and Chad by extension officers (or similar staff) from the other producing countries. Finally workshops/seminars for representatives from the public and the private sector dealing with gum arabic quality control could also be organised as part of the training initiative.

It was also recommended that:

Characterisation and specification of gum arabic.

References

FAO (1995). Food and Nutrition, No. 52. Add.3.

 


THE CHEMICAL CHARACTERISATION OF MYRRH AND FRANKINCENSE AND OPPORTUNITIES FOR COMMERCIAL UTILISATION

DR. K. A. KARAMALLA
Dept. of Food Science and Technology
Faculty of Agriculture
University of Khartoum
Khartoum, SUDAN.

Introduction

Oleo-gum resin is an exudate, essentially mixture of volatile oil, resin and gum, obtained by incision from the plant family Burseraceae. Oleogum-resin obtained from the genus Boswellia is olibanum or frankincense while that obtained from genus Commiphora is myrrh.

There are about 12 species of the genus Boswellia in North, East Africa and Southern Arabia (Howes, 1949). Boswellia serrate is an Indian variety, while Boswellia carterii and B. papyrifera are African varieties.

On the other hand, there are about 160 species of the genus Commiphora. All are African with the exception of 12 species which occur from S. Arabia to India. Commiphora africana is indigenous to Africa while C. abyssinica is found in S. Arabia and E. Africa.

Chemical composition

Oil

It has been reported (Hough et al., 1952; Treas and Evans, 1978; Abdel et al ., 1987) that olibanum from B. carteria contains 60-70% resin and 3-8% volatile oil. In contrast, myrrh contains 25-40% resin and 7-17% volatile oil. Recently (Karamalla, 1997) ethanol-extracted oil has been found to be 72.1, 72.2, 7 and 95.9% while steam-distilled oil has been found to be 2.8, trace, and 9.6 for B. papyrifera, C. africana and C. abyssinica oleo gum resins respectively.

Twenty -seven sesquiterpene hydrocarbons have been identified (Yates and Wenninger, 1970) in the oil of Boswellia spp obtained by steam distillation.

The volatile oil of myrrh has been shown (Treas and Evans, 1978) to contain terpenes, sesquiterpenes, esters, aldehydes and alcohols while that of olibanum has been found to consist of numerous terpenes and sequiterpenes.

Seven sesquiterpenes hydrocarbons, a furanosesquiterpenoid oil and furanoidiene have been detected (Graveiro et al., 1983) in the volatile oil of C. quidotti.

A study (Provan et al,.1987) of the volatile portions of resins from a number of Kenyan species of Commiphora has shown that these oils consist mainly of monoterpenoids or sesquiterpenoids.

Two triterpenes have been identified in the resins of C. incisa and C. kua and their potential chemotaxonomic significance indicated (Provan and Waterman, 1988).

Thirty-three constituents have been identified in the steam distilled oil of B. carterii, eleven of which were not detected in the n- hexane extract. The oil contained 62.1% ester, 15.4% alcohol, 9.9% monoterpene hydrocarbons and 7.1% diterpenes (Abdel et al ., 1987).

The resins of C. terbinthina and C. cyclophylla have been shown (Abegaz et al., 1989) to consist primarily of moneterpene hydrocarbons with limonene as a major component. However, the resin of C. terbinthina is rich in sesquiterpenes.

The carbohydrate component of Oleo-gum resins

Content

Extraction of gum myrrh with 90% alcohol gave a crude polysaccharide (PS) that ranged in yield from 27 to 61% (Hough et al., 1952, Treas and Evans, 1978; Hirst and Jones, 1981). On the other hand, gum olibanum on similar treatment gave a crude polysaccharide that ranged from 27-35%.

Recently (Karamalla, 1997) the carbohydrate component contents of B. papyrifera, C. africana and C. abyssinica have been found to be 27.9, 27.3 and 4.1% respectively.

Protein content

It has been reported (Hough et al., 1952,) that the crude PS of myrrh contained 18% protein, and that the purified PS from B. papyrifera has only 4-8% protein (Anderson et al., 1965). Recently (Abdel Kariem, 1992) the protein content of the crude PS of B. papyrifera has been found to be 3.9%.

The crude acidic PS of gum myrrh has an equivalent weight of 547 (Hough et al., 1952) and that of B. carterii has an equivalent weight of 540 (Jones and Nunn, 1955).

Very recently (Karamalla, 1997), 614 and 628 have been reported as values for the equivalent weight of PS from B. papyrifera and C. africana respectively.

Specific rotation

Specific rotation for frankincense of B. carterii and that of gum myrrh have been reported (Jones and Nunn, 1955) to be -8o and +32o respectively. For gum from B. papyrifera a value of -4o for the specific rotation has been reported (Abdel Kariem, 1992).

Very recently (Karamalla, 1997) PS from B. papyrifera and C. africana have been found to have specific rotation of -11o and -26o respectively

Sugar composition

Complete hydrolysis of PS from B. papyrifera (Anderson et al ., 1965) has afforded uronic acid 19%, D-galactose 60% L-arabonose 10% and L-rhamnose 5% plus a trace of L-fucose. Recently (Abdel Kariem, 1992) PS from B. papyrifera has been found to contain D-galactose 35%. L-arabinose 12% uronic acid 20% with traces of L-rhamnose and L-fucose. Very recently (Karamalla, 1997) it has been shown that the sugar composition of PS of B.papyrifera is L-arabonose 12.7%, LL-rhamnose 13.7%, L-fucose 13.1%, D-galactose 18.7%, D-glucuronic acid 25.3% and 4-0- methyl-D-glucuronic acid 13.8% white PS from C. africana afforded L-arabinose 20.2%, L-rhamnose 19.7%, L-fucose 17.6%, D-galactose 19.6%, and D-glucuronic acid 22.8%.

Heterogeneity of PS

Solvent fractionation yielded a number of PS fractions for myrrh and olibanum that varied in yield, solubility in water and alkali, specific rotation and molar proportions of D-galactose and L-arabinose (Hough et al., 1952). This finding has recently (Karamalla, 1997) been confirmed by acetone fractionation of the polysaccharide from B. papyrifera, indicating once more the heretogeneity of plant gums.

Utilisation

Exports of gum olibanum and gum myrrh have been increasing in recent years with a rapid rise in production and earning, indicating expanding utilisation of these oleo-gum resins.

Historically, myrrh has been used by the ancient Egyptians in embalming and as a chewing gum (Hirst and Jones, 1981). Now oleo-gum resins are widely used in perfumes, medicine and as insecticides.

(i) Perfumes

The gum resin of C. africana melted with water is used as a perfumed application to the body (Watt and Berger, 1962). Olibanum is used as odourous fragrance which last for a very long time and is an excellent fixative for perfumes for men. Oleo-gum from B. carterii and from B. wightii is widely used as an incense in religious ceremonies for example (Elamin, 1981). Oil of B. serrate is used in the soap and perfumery industry (Karnik and Sharma, 1970).

It has been suggested that the alcohol soluble resins oil of olibanum has much more fixation properties than the volatile oil. However, the reverse is true of myrrh.

Oleo-gum from B. papyrifera is used widely as incense in holy places and temples and also to perfume houses (Elamin, 1981).

(ii) Medical uses

Myrrh is a disinfectant and may be used as a local stimulant to the mucous membrane (Howes, 1949). The resin of B. carterii is used as a diuretic. It is boiled with sesame oil and taken daily for bilharzia. A decoction made with cinnamon and cardamon is used for the relief of stomach-ache. In India, oleo-gum resin is used as a remedy for rheumatoid and diseases of nervous system, and is an ingredient of certain ointments (Watt and Berger, 1962).

Oleo-gum resin from C. wightii is considered as astringent, demulcent, expectorant, carminative aphrodisiac and antiseptic (Elamin, 1981) it has also been used for treating rheumatoid arthritis, heart ailments, neurological disorders, skin infections, and obesity in humans. An extract from the resin of some species of Burseraceae has been known to have anti-inflammatory activities.

(iii) Insecticides

Myrrh is used as an insecticide especially as a repellent of termites and as a mosquito repellent when blended as incense sticks (Elamin, 1981).

Essential oil from B. serrata is found to affect spermatogenesis in Dysdercus similis, thereby acting as an effective insect growth regulator. Constituents of the resin from C. rostrata have repellent effects against the maize weevil. The effect of gum resin of B. papyrifera and C. africana on three insect pests of economic importance, has led to morphological malformation of adults and pupa, reducing the emergence of adults and increasing mortality rate.


References

Abdel Kariem, E. H., (1992). Structural Studies of Some Sudanese Gums. Ph.D. Thesis Faculty of Science University of Khartoum.

Abdel Wahab, S.M.., Aboutable, E.A., El-Zalbeni, S.M.,. Fouad. H.A., De Pooter, H.I., and El- Fallaha B. (1987). The essential oil of olibanum. Planta Medica 52, 382-384.

Abegaz B., Dagne, E.,. Bates C. and Waterman, P.G. (1989) Monoterpene -rich resins from two Ethiopian species of Commiphora. Flavour and Fragrance Journal 4 (30., 99-101.

Anderson, D.M.W., Cree, G.M., Marshall, J.J. and Rahman, S. (1965). Studies on uronic acid materials Part XI. The carbohydrate component of the oleo-resin from B. papyrefera. Carbohydrate Research 1-320-323.

Elamin (1981). Trees and Shrubs of the Sudan. Ph.D. Thesis, Faculty of Science, University of Khartoum, Sudan.

Graveiro, A., Corsano, S., Proitti, G. and Strappaghetti G. (1983). Constituents of essential oil of C. guidotti. Planta Medica, 48 (2), 97-98.

Hirst E. I. and Jones, J.F.N. (1981). Chemistry of Plant gums: Research 4.411.

Hough, L., Jones, J.K.N. and Wadman (1952). Some observation on the constituents of gum myrrh. J. Chem. Soc. 795-797.

Howes, T.N (1949). Vegetable Gums and Resins pp 199-182, Chronica Botanica Co, Waltham, Mass. USA

Jones, J.K.N. and Nunnn, J.R. (1955). The Structure of Frankincense gum. J. Am. Chem. Soc. 77.8745.

Karamalla, K. A. (1997). Unpublished results, Faculty of agriculture, University of Khartoum, Sudan.

Karnik, M.G. and Sharma, O.R. (1970). Further studies on the distribution and utilization of oleo-gum resin of B. serrata. Indian Drugs 96 (1) 843-848.

Provan, G.J., Gray, A.I., and Waterman P.G. (1987). Monoterpene -rich resins from some Kenyan Burserceae.

Provan, G.J., and Waterman, P.G. (1988). Major triterpene from the resin of C. incisa and C. kua and their potential chemotaxonomic significance.

Treas. G.E. and Evans, W.C. (1978). Volatile oils and resins pharmacognosy pp. 463-464 B. Tindall, London.

Watt, J., and Breger, M.G. (1962). The Medicinal and Poisionausss Plants of Southern and Eastern Africa pp 151-153. Livingstone Ltd. Edinugh and London

Yates, R.L. and Wenninger, J.A. (1970). Constituents of olibanum oil sesquiterpene hydrocarbons. J. of Association of Official Analytical Chemists, 53, 941-980.

 


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