Locust bean (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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Locust bean (or carob) gum is the whitish powder obtained from grinding the endosperm of the seeds of Ceratonia siliqua, a tree widely cultivated in the Mediterranean region. It consists mainly of galactomannan-type polysaccharides, with a galactose:mannose ratio of about 1:4.

Unlike guar gum (produced from Cyamopsis tetragonoloba), locust bean is only partially soluble in cold water, but it has better water retention characteristics than guar. Solutions of locust bean gum have relatively high viscosities at low concentrations. Dispersions of the gum do not gel well unless it is in combination with other gums. Its strong synergistic action in the presence of other gums contributes to it having wide applications where good stabilizing, thickening and emulsifying properties are required.

Uses of locust bean gum are divided between food and other, miscellaneous applications.

Food use

Its use as a food additive is the most important outlet for locust bean gum. In European Community legislation it has an "E" number of E410. It is employed in a wide range of products, among the most important of which are ice cream, baby foods and pet foods. In these applications its texturizing properties are of great value and hard to replicate using other gums; in ice cream the gum slows the rate of melt-down and improves its storage properties.

Locust bean gum is an important constituent of many soups, where its property of fully dissolving and thickening only at high temperatures is critical. In sausage products such as salami and bologna it acts as a binder and lubricant. Other food uses include the manufacture of soft cheeses, bakery products, pie fillings, powdered desserts, sauces and salad creams, and dairy products other than ice cream.

Miscellaneous applications

The paper industry used to be the biggest consumer of locust bean gum and its derivatives, but its use in this field has diminished considerably. It was added during the paper-making process to improve the physical characteristics of the paper.

In the textile industry, locust bean is used either alone or in combination with starch and synthetics as a sizing agent for cotton and other natural fibres. It is also used as a print-paste thickener in both roller and screen printing to help provide greater purity and uniformity of shades and deeper penetration of dyes.

Other, minor uses include incorporation in oil-drilling fluids, and some pharmaceutical and cosmetics applications.

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Markets

ROBBINS (1988) details exports and imports for most of the major countries concerned for the years 1979-85, and most of the following discussion draws on his data. Up-to-date information on Japanese imports of locust bean gum, 1988-94, are provided in Table 15.

Robbins estimated total world exports of locust bean gum at about 12 000 tonnes/year. In the period covered by his report, Western Europe was the biggest market (and still is), although substantial quantities are re-exported. Within Europe, the United Kingdom was the biggest importer (averaging about 2 900 tonnes annually), with Germany the next biggest (about 1 700 tonnes/year). The United States' imports averaged 2 300 tonnes/year but were in decline due to prevailing high prices at the time.

Japan is another major market and imported an average of 1 500 tonnes/year during 1979-85. The more recent data given in Table 15 (1988-94) gives an average level of imports of just under 1 700 tonnes/year, not much different to the earlier figure.

At the time of Robbins' report, high prices were posing problems for end-users and there was evidence that locust bean gum was suffering partial substitution by a number of alternatives, notably xanthan gum, carboxy-methylcellulose and modified starches. Since that time, although prices recovered somewhat, they have recently been increasing again; this has been due to a crop shortage in 1994 caused by droughts in the Mediterranean region. In the United States, carrageenan has been making up some of this shortfall.

Supply sources

Estimates over the last 10 years of world production of pods have been in the range 350 000-500 000 tonnes/year. The main gum-producing countries are Spain, Italy and Portugal. Robbins estimated their contributions to the 12 000 tonnes total annual production of locust bean gum to be about 5 000 tonnes, 3 000 tonnes and 1 500 tonnes, respectively. The remaining 2 500 tonnes was accounted for mainly by Morocco, Greece, Cyprus and Algeria. Turkey, Israel, India and Pakistan produce locust bean but were not, then, believed to be significant traders of gum.

Exports of locust bean seed from Cyprus for 1988-92 are shown in Table 16. Apart from the United Kingdom, all other exports from Cyprus go to the three main gum producers, Spain, Italy and Portugal. The level of exports fluctuated but averaged approximately 1 000 tonnes/year.

All the major producers of locust bean gum are shown as recent sources of imports into Japan (Table 15), together with smaller producers such as Greece, India and Morocco, but the data also highlight the extent of re-exports from such countries as Denmark, Netherlands and the United States.

Quality and prices

A number of grades of locust bean gum are available, and for each grade it is possible to have different particle sizes according to the requirements of the end user. The highest grades are in the form of a near-white powder, free from specks of seed hull; particles of

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seed germ, produced during the primary processing of the seed, are at a minimum. The top grades have the highest viscosity. An average quality gum contains about 12% moisture.

An FAO specification exists for "carob bean gum" employed in foods and this specifies upper limits on such things as moisture content, acid-insoluble matter and protein, as well as arsenic, lead and heavy metals.

An ISO specification also exists but this is for carob pods intended for human consumption, forage or industrial use, and not the seeds or gum.

Current (mid-1995) prices of gum, following a short crop, are very high, in the range US$ 24-30/kg. Prices are expected to fall back to a third of this when the new crop becomes available in September/October.

Botanical/common names

Family Leguminosae (Caesalpinioideae):

• Ceratonia siliqua L. - Locust bean, carob, St John's bread

Description and distribution

Ceratonia siliqua is a long-lived evergreen tree, up to 15 m tall in favourable conditions in the wild, but under cultivation it is much smaller. It displays great variation in biological form and floral types; in unfavourable habitats it takes a shrubby form with multiple stems. A large number of named cultivars have been developed. The size, shape and thickness of the pod containing the seeds varies greatly depending on the cultivar, but up to 18 hard, brown seeds are contained in each pod; the pod may be up to 30 cm long.

The tree thrives under the hot, dry summers and cool, wet winters of the Mediterranean climate and it is distributed throughout the Mediterranean region. Its cultivation is centred on Spain, Italy and Portugal, but is also undertaken in southern Greece, Turkey, Israel, Lebanon, Syria, Cyprus and other islands in the Mediterranean. More recently, commercial exploitation has developed significantly in several North African countries, including Morocco and Algeria. It has also been introduced to the warmer parts of the United States, Mexico, South Africa, Australia and India.

The first commercial fruits can be harvested after about 5-7 years. After flowering, the pods take about 6-8 months to mature, turning from green to chocolate brown in late summer. They are usually harvested by knocking them off with long poles, preferably aimed at the bunches of pods themselves rather than by indiscriminate beating of the branches.

The harvested pods are taken to the kibbling factories where they are left to dry for about a month. They are then crushed and broken in the kibbling machines, which are usually of the hammer mill type, and put through a series of sieves which sorts the broken pieces according to size. The seeds are further separated from pieces of pod of the same size by blowing air through the mixture.

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The seeds usually comprise 8-10% of the pod by weight. The approximate composition of the seed (by weight) is:

Locust bean gum (endosperm) may therefore comprise as much as half of the seed's weight.

The separation of the seed components is a process which requires careful conditioning of the seed prior to fractionation, as well as expensive machinery, and is not always carried out in the country where the pods are harvested. However, because separation of the endosperm constitutes the first stage of gum production, the basic principles of the process are described here, rather than under VALUE-ADDED PROCESSING.

Details of the processing are not public knowledge but the first stage involves removal of the seed hull. This is achieved either by mechanical abrasion or by chemical treatment. In one method, the seeds are roasted, which loosens the hull and enables it to be removed from the rest of the seed; the remaining part is cracked and the crushed germ, which is more friable than the endosperm, is sifted off from the unbroken endosperm halves. An alternative method is to treat the whole seed with acid at an elevated temperature; this carbonizes the hull, which is removed by a washing and brushing operation, and the dried germ/endosperm is then processed as before. Efficient removal of the hull prior to separation of the germ and endosperm is important since residual specks of it will detract from the quality and value of the final product. The pieces of endosperm are then ground to the required particle size to furnish locust bean gum.

Yields

Yields of pods are extremely variable and depend very much on the cultivar in question, as well as climatic and other conditions where the trees are growing. Individual trees have been reported to yield up to 0.5-1.0 tonne of pods but average yields in cultivated stands rarely exceed 2.5 tonnes/ha. Average yields in Cyprus for 1967 (based on 55 000 tonnes production) were equivalent to approximately 2 tonnes/ha or 22 kg/tree. However, another report gives much higher yields: average yields in Cyprus, Israel and Mexico are stated to be equivalent to 10-17 tonnes/ha. Yields increase steadily up to 25-30 years of age, but may vary in alternate years, being high one year and low the next. Well cared for cultivated trees have a productive life of 80-100 years.

Further processing involves either chemical modification of the gum or blending with other gums to produce a final product with a range of physical and functional properties designed to suit the end-user's requirements.

Locust bean pods, after grinding into a flour, have traditionally been used as a source of low-grade protein in animal feeds. The pods are especially rich in sugars and are very palatable

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to cattle and pigs. However, they also contain appreciable amounts of tannins, which reduce digestibility of the protein, and locust bean meal is usually limited to around 10% incorporation in the feed. Germ meal - which is separated from the rest of the seed during gum production - is richer in protein and free of the tannins, and can be used at a higher level of incorporation in feeds, and in all classes of livestock.

The high carbohydrate content of the pod husks enables them to be used for the production of a sugar syrup. Some research has been carried out on the possible use of this syrup as a substrate for microbial protein production. The extracted sugars can also be fermented to alcohol.

In recent years, toasted carob flour produced from the pods has been widely used as a chocolate substitute, particularly in bakery and confectionery products and low calorie snack foods.

Ceratonia siliqua has a number of attributes which make it well suited to promotion as a multipurpose tree in the drier parts of the world. It grows on a wide variety of soils, including marginal and rocky ones, and requires relatively little attention. It is reasonably drought resistant, although it needs some rain if it is to yield commercial quantities of pods. In return, it offers feed (for animals) and, in times of hardship or famine, food for human consumption. It also provides shade and shelter.

If it is intended to develop locust bean as a crop for international trade, rather than local use, then the labour-intensive nature of the harvesting and the increasing costs of labour in southern Europe give some advantages to potential producers in developing countries.

Research needs

If the developmental potential of Ceratonia siliqua is to be realized in countries outside its present area of exploitation, then the following research needs must be addressed:

• Market information. Information should be sought on the prospects for local use of

pods for animal feeds and other uses, and on the export markets for seeds (since it is unlikely that production of gum itself will be feasible).

• Germplasm selection. Planting trials should be carried out, and pod/seed yields per hectare determined, for a range of cultivars tentatively judged to be most suitable for developing countries according to the particular climatic and edaphic conditions.

• CARLSON, W.A. (1986) The carob: evaluation of trees, pods and kernels. The International Tree Crops Journal, 3, 281-290.
• CATARINO, F. (1993) The carob tree - an exemplary plant. Naturopa, 73, 14-15.
• CHARALAMBOUS, J. (1966) The Composition and Uses of Carob Bean. Nicosia, Cyprus: Cyprus Agricultural Research Institute.

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• COIT, J.L. (1951) Carob or St John's bread. Economic Botany, 5, 82-96.
• DAVIES, W.N.L. (1970) The carob tree and its importance in the agricultural economy of Cyprus. Economic Botany, 24, 460-470.
• DUKE, J.A. (1981) Ceratonia siliqua. pp 50-52. In Handbook of Legumes of World Economic Importance. 345 pp. New York: Plenum Press.
• FAO (1992) Carob bean gum [published in FAO Food and Nutrition Paper 49, 1989]. pp 377-380. 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.
• GRAINGER, A. and WINER, N. (1980) A bibliography of Ceratonia siliqua, the carob tree. The International Tree Crops Journal, 1, 37-47.
• HILLS, L.D. (1980) The cultivation of the carob tree (Ceratonia siliqua). The International Tree Crops Journal, 1, 27-36.
• ISO (1987) Carob. International Standard ISO 7907-1987. 4 pp. International Organization for Standardization.
• NAS (1979) Carob. pp 109-116. In Tropical Legumes: Resources for the Future. 331 pp. Washington, D.C., USA: National Academy of Sciences.
• ROBBINS, S.R.J. (1988) Locust bean gum. pp 67-72. 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].
• ROL, F. (1973) Locust bean gum. pp 323-337. In Industrial Gums. Whistler, R.L. (ed.). 810 pp. New York: Academic Press.
• SINGH, D. (1961) Get acquainted with the carob. Indian Farming, 11(2), 12 and 40.
• WIELINGA, W.C. (1990) Production and applications of seed gums. pp 383-403. In Gums and Stabilisers for the Food Industry, Vol. 5. Proceedings of 5th International Conference, Wrexham, July, 1989. Oxford: IRL Press.
• WINER, N. (1980) The potential of the carob (Ceratonia siliqua). The International Tree Crops Journal, 1, 15-26.

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Source: National statistics

Source: National statistics

1. ↑ Includes decorticated, crushed or ground seed and non-decorticated seed