Karaya (FAO, NWFP 6)

← Gum arabic

Coppen, Gums, resins and latexes of plant origin, 1995

Tragacanth →

• 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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2 - EXUDATE GUMS

KARAYA

DESCRIPTION AND USES

Karaya gum is the dried exudate obtained from trees of Sterculia species. Most gum is of Indian origin, although increasing amounts come from Africa. The gum enters trade as irregular-shaped or broken tears, with colour ranging from whitish or tan in the better grades to dark brown in the lower grades. In the early years of large-scale, commercial use it was sometimes used as an inferior substitute for tragacanth, and this led to its alternative name of Indian Tragacanth.

Karaya is an acidic, partially acetylated polysaccharide. It absorbs water very rapidly to form viscous mucilages at low concentrations, although it is one of the least soluble of the gum exudates. Although it does have food use - in Europe it has been assigned the food additive number E416 - its usage is overwhelmingly in pharmaceutical, dental or other medical applications, particularly those which make use of karaya's strong adhesive properties. A very minor amount is used in miscellaneous industrial applications such as papermaking and textiles.

Pharmaceutical and related use

The three most important uses of karaya are as a dental adhesive for false teeth, in the manufacture of colostomy bag fixings, and as a bulk laxative. In the first two applications there has been some substitution of karaya by cheaper carboxymethylcellulose derivatives, although recent American trade reports have suggested that some of these substitutes are not as effective as karaya. An Indian market study (ANON., 1987) reported that in France and the United Kingdom, 95% of imported karaya is used in pharmaceutical products; in the United States and Japan, the proportion was about 85%.

Food use

In foods, karaya is used in small amounts as a texturizer and stabilizer in ice creams, and in ice sherbets to prevent the formation of ice crystals. Its stability in acid media makes it suitable for addition to salad dressings, sauces, cheese spreads and some other products.

WORLD SUPPLY AND DEMAND TRENDS

Markets

Throughout the late 1960s to mid-1980s, Indian exports of karaya were in the range 4 000-6 000 tonnes/year - more than that of all other Indian gums and resins combined - and the United States, France and the United Kingdom (in that order) were the biggest importers. Average exports for the period 1977/78-1982/83 were approximately 5 700 tonnes/year (ROBBINS, 1988).

More recent data, for the years 1987/88-1993/94, are given in Table 13. The six-year annual average for 1987/88-1992/93 is less than 1 300 tonnes, a sharp decline on the same period a decade earlier. The United States, France and the United Kingdom remain the biggest markets for karaya, although demand in the United States has fallen to such a degree that France is now the main importing country. Approximate annual averages over the whole

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of the recent period are: France 400 tonnes, United States 360 tonnes and the United Kingdom 210 tonnes; Japan is the next biggest single market (110 tonnes). Germany, Italy, Belgium and the Netherlands have also imported directly from India in most years (averaging 130 tonnes/year between them) so Europe as a whole is about twice the size of the American market.

Indian government controls over pricing and exports of karaya in the late 1980s, which some trade sources feel contributed to the poor supply situation caused by restrictions on tapping and low productivity, have now been relaxed, although there are mixed views in the trade as to whether karaya can regain its former position in the international market.

India is traditionally the biggest producer and exporter of karaya but increasing amounts of gum enter international trade from Africa. The quantities involved are very uncertain but if the data for Senegal in Table 2 (imports into the EC of gums and resins excluding gum arabic) refer mainly to karaya, then they could amount to around 1 000 tonnes or more annually.

Domestic consumption of karaya in India was (and still is) considerable. No recent data are available but in 1972, for example, it was about twice the volume of exports.

Supply sources

India remains the biggest producer of karaya and, apart from lac, karaya is still India's most important export item in the gums and resins category. However, the data in Table 13 indicate a sharp fall in exports in 1990/91 from the previous year, with an all-time low of 570 tonnes in 1991/92. It is not known to what extent supplies from Africa made up for the drop in Indian exports. Since then, Indian exports have recovered somewhat, although they are still below the level at the beginning of the period shown in Table 13, and considerably below the levels a decade earlier.

In Africa, Senegal is the biggest producer of karaya and significant quantities are exported to France and the United Kingdom. Sudan also exports small amounts although it has the potential to produce and export much more.

Quality and prices

There are at least five Indian grades of karaya: HPS (Hand Picked Selected), Superior No.1 and No. 2, FAQ (Fair Average Quality) and Siftings. The first four grades are the main export grades. The main quality criteria at the sorting stage are colour and foreign matter, although even after grading the quality of consignments is often variable. The higher grades should be cleaner and paler than the lower ones, which may be dark brown in colour and have bits of bark present.

A BP specification exists for pharmaceutical grade karaya, and FAO and Indian specifications have been published for karaya intended for food use.

Indicative FOB prices quoted by importers in London for Indian karaya (mid-1995) are in the range US$ 2 250-6 000/tonne according to grade. FAQ gum is about US$ 3 000/tonne. Senegalese gum has two grades, hand-picked and standard, which are generally inferior to the Indian export grades, and this is reflected in lower prices.

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PLANT SOURCES

Botanical/common names

Family Sterculiaceae:

• Sterculia urens Roxb.
• Sterculia villosa Roxb.
• Sterculia setigera Del.

Description and distribution

Sterculia urens is a deciduous tree, up to 15 m high. It has a smooth, greyish white or reddish bark, which peels off in papery flakes. In India it occurs wild in many places on the dry, rocky hills and plateaus of central and northern regions, but it is also grown in plantations as a timber crop. The greater proportion of recent production has come from Andhra Pradesh state.

Sterculia villosa is a small to moderate sized, spreading tree, distributed in the sub-Himalayan tract of India from the Indus eastwards, as well as more southern regions.

Several species of Sterculia occur in Africa but Sterculia setigera is the only species known to be exploited commercially for gum. It grows up to 15 m tall and has papery, peeling bark.

COLLECTION/PRIMARY PROCESSING

There is some natural exudation of karaya but most gum is collected by tapping. Descriptions of the tapping vary somewhat according to the source of the information, but all entail removal of sections of bark from the trunk of the tree. Guidance rules have been laid down by the Forest Research Institute, Dehra Dun, in India, but in practice the rules are not adhered to and the dimensions of the "blaze" are often exceeded. Tapping which involves deep and wide wounds to the tree to maximize gum yields is damaging to the tree, and this led to a ban on tapping by one Indian Forestry Department in the 1980s.

In India, tapping should be confined to trees with a minimum girth of 90 cm and the initial size of the blaze should be limited to 15 cm tall, 10 cm wide and 0.5 cm deep. Sixteen successive visits should be made to the tree at two-week intervals, removing a further 2-cm high section of bark above the previous one at each visit, and leading to a maximum depth of the blaze of 2.5-3.0 cm. An additional blaze can be worked for every 50 cm girth increment above 90 cm, providing sufficient space is left between adjacent blazes. By staggering the position of each new season's blazes it is possible to leave a rest period of six years before returning to a previous one, by which time the scar should have healed. Tapping is best done during the hot season to maximize yields.

In India, the collected gum is usually sold by auction to government agencies in each of the producing states, who then undertake final cleaning, drying and grading of the gum.

Yields

No reliable data are available but the yield of gum from mature trees has been variously estimated at 1-5 kg/tree during a season.

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VALUE-ADDED PROCESSING

Imported gum is purified by size reduction and removal of pieces of bark by air flotation methods. Other mechanical methods are used to remove sand, dirt and other types of foreign matter.

PRODUCTS OTHER THAN GUM

The wood finds some use although it is not a high class timber. It has been employed for making packing cases, match splints, pencils, picture frames and other miscellaneous items.

DEVELOPMENTAL POTENTIAL

The market appears willing to take good quality gum if it is available, as evidenced by the recent upturn in Indian exports, and pharmaceutical usage of karaya seems to be firm. However, opportunities for exploiting market demand are likely to rest more with existing producers, especially those in Africa with underexploited stands of Sterculia, than with new ones. Sudan has very large areas of Sterculia and if attention is paid to harvesting and cleaning the gum to produce material of high quality - as it is for gum arabic - then it certainly has the potential to supply much larger quantities of gum than it does at present.

Research needs

Improvement of harvesting, cleaning and handling practices, coupled with market studies, is required more than basic research. Trade evaluation should be undertaken of large, representative collections of gum, by those countries having the raw material resource, in order to ascertain the scope for increased production and to gain the confidence of end-users that they would be a reliable, consistent supplier of gum.

SELECTED BIBLIOGRAPHY

• ANON. (1973) Karaya Gum from Sterculia Urens Roxb. Industrial Series No. 7. Dehra Dun, India: Forest Research Institute and Colleges.
• ANON. (1976) Sterculia. pp 43-49. In The Wealth of India. Raw Materials, Vol. 10. New Delhi: Council for Scientific and Industrial Research.
• ANON. (1987) Market Survey for Select Minor Forest Products in France, UK, USA and Japan. 157 pp. New Delhi: Indian Institute of Foreign Trade.
• BABU, A.M. and MENON, A.R.S. (1989) Ethephon-induced gummosis in Bombax ceiba L. and Sterculia urens Roxb. Indian Forester, 115(1), 44-47.
• BP (1993) Sterculia. p 631. In British Pharmacopoeia, Vol. 1. London: Her Majesty's Stationery Office.
• BIS (1985, reaffirmed 1990) Specification for gum karaya. Indian Standard IS: 5025-1985. 6 pp. New Delhi: Bureau of Indian Standards.
• BIS (1988) Specification for gum karaya, food grade. Indian Standard IS: 12408-1988. 6 pp. New Delhi: Bureau of Indian Standards.

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• FAO (1992) Karaya gum [published in FAO Food and Nutrition Paper 38, 19881. pp 821-823. In Compendium of Food Additive Specifications. FAO Food and Nutrition Paper 52 (Joint FAO/WHO Expert Committee on Food Additives. Combined Specifications from 1st through the 37th Meetings, 1956-1990). Rome: Food and Agriculture Organization.
• GAUTAMI, S. and BHAT, R.V. (1992) A Monograph on Gum Karaya. Hyderabad, India: National Institute of Nutrition, Indian Council of Medical Research.
• GOLDSTEIN, A.M. and ALTER, E.N. (1973) Gum karaya. pp 273-287. In Industrial Gums. Whistler, R.L. (ed.). 810 pp. New York: Academic Press.
• GUPTA, T. and GULERIA, A. (1982) Gums and resins. pp 73-84. In Non-Wood Forest Products in India: Economic Potentials. 147 pp. New Delhi: Oxford & IBH.
• JAYASINGHE, S. (1981) Plant gum exudates - an unexploited forest resource of Sri Lanka [includes Acacia and Sterculia spp.]. The Sri Lankan Forester, 15(1-2), 54-60.
• ROBBINS, S.R.J. (1988) Gum karaya. pp 61-66. In A Review of Recent Trends in Selected Markets for Water-Soluble Gums. ODNRI Bulletin No. 2. 108 pp. London: Overseas Development Natural Resources Institute [now Natural Resources Institute, Chatham].
• SHAH, J.J. (1983) Gum, resin and gum-resin secretion in plants. Acta Botanica Indica, 11(2), 91-96.
• SHIVA, M.P., SINGH, N.P. and THAKUR, F.R. (1994) New designed improved gum tapping tools. MFP News (Centre of Minor Forest Products, Dehra Dun, India), 4(1), 8-11.
• SINGH, M. (1981) Potentialities for gum collection in Maharashtra and Gujurat. Khadi Gramodyog, 27(5), 288-290.
• VERMA, V.P.S. and KHARAKWAL, G.N. (1977) Experimental tapping of Sterculia villosa Roxb. for gum karaya. Indian Forester, 103(4), 269-272.

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Table 13. Karaya: exports from India, and destinations, 1987/88-1993/94 (tonnes)

	87/88	88/89	89/90	90/91	91/92	92/93	93/94
Total	2001	1831	1628	599	574	843	1443
Of which to:
USA	708	604	467	215	105	178	287
France	543	466	496	124	112	373	729
UK	485	346	305	17	52	118	181
Japan	123	113	138	78	132	78	133
Germany	58	167	122	50	61	44	35
Italy	48	59	30	50	30	23	16
Belgium	6	14	26	10	34	-	5
Netherlands	5	10	-	15	15	7	-
Thailand	5	1	8	6	-	7	23
Malaysia	8	4	2	-	1	-	3
Singapore	6	1	1	4	1	8	5
Norway	-	21	-	25	7	5	-
Czechoslovakia, former	-	22	-	-	-	-	-
Oman	-	-	13	-	-	-	-
Bermuda	-	-	13	-	-	-	-
Hong Kong	-	-	5	-	-	-	-
United Arab Emirates	-	1	-	-	19	-	19

Source: National statistics