Locust Bean Gum

LOCUST BEAN GUM

Synonyms

Arobon, Carob gum, Ceratonia.

Biological Source

This gum consists of endosperms of the seeds of Ceratonia siliqua Linn., belonging to family Leguminosae.

Geographical Source

The plant is found in Cyprus, Sicily and Egypt. It is cul-tivated easily but very sensitive to low temperature. It is produced in Spain, Greece, Algeria, Morocco, Israel, Italy and Portugal.

History

The cultivation of locust bean trees was known before Christian era. Dioscorides referred its curative properties in the first century A.D. In Sicily, the carob trees were probably planted in 16th century. Arabs used carob seed as a unit of weight and it was labelled as carat, which in turn has become unit of weight for precious stones.

Cultivation and Collection

Carob is an evergreen tree growing to a height of about 10 m and has luxuriant perennial foliage. The tree grows on rocky soil and has very long roots that penetrate up to 18–25 m and survive in an area where there is very little rain fall.

It starts bearing fruits only after three years. The plants start flowering in January to March every year, and the fully matured fruits are ready by October–November. The fruits (pods) are harvested by shaking the twigs and picked up from the earth by hand and sent to market.

The locust bean fruits or carob are dark chocolate coloured, 10–20 cm long, 2.0–5 cm wide and 0.5–1.0 cm thick. The seeds are ovoid dark brown, very hard and weigh 0.21 g or 3.2 grains (i.e. one Carat). The locust bean tree can be planted or even grafted.

Preparation and Purification of Gum

Locust bean pods consist of 90% of pulp and 8% of kernels. The pods are fed to kibbling machine. The kernels separated consist of 30–33% of husk, germ (about 25%) and endosperm (42–46%). Preparation of high quality gum consists of separation of endosperm from embryo. Successful removal of outer dark coloured husk decides the quality of the gum. Decorticated seeds (dehusked seeds) split lengthwise and are separated from the embryo. The presence of yellow germ (i.e. embryo) increases the rate of fermentation of the gum solutions in further products. Hence, it must be thoroughly removed from the endosperm. It is then pulverized and graded according to the mesh size. The normal mesh sizes available in Italian market are 150, 175 and 200.

Description

Chemical Constituents

Locust bean gum contains about 88% of D-galacto-D-man-noglycan, 4% pentan, 6% protein, 1% cellulose, and 1.0% ash. The ratio of D-galactose to D-mannose is approximately 20:80. Commercial locust bean gum contains no specks and gum particles should not exceed 8–10%. The natural moisture content of gum is about 14.0%.

Identification Test

Locust bean gum mucilage when boiled with 5.0% potassium hydroxide solution becomes clear and shows no yellow colour as in agar and tragacanth or brown colour as in sterculia gum.

Uses

It is useful as a stabilizer, thickner and binder in cosmetics; adsorbent and demulcent therapeutically. It is used as sizing and finishing agent in textiles and also as drilling mud addi-tive. In food industry, it is used as substitute for starch.