Cluster bean (Cyamopsis tetragonolobus) also locally known as guara or guar is important leguminous crop of autumn season. It is multipurpose crop grown for fodder, green manure, vegetable as well as for grain purpose but it is mostly grown for grain purpose because its endosperm contain 68-70 per cent galactomannan, which is marketable product in the form of guar gum. This chemical has its application in textile, paper, mining, petroleum, pharmaceutical, explosive and food industries. Cluster bean is mainly grown in India, Pakistan, United States, Sudan, South Africa, Brazil, Malavi, Zaire and some parts of Australia. India followed by Pakistan and USA are key producers of guar seed. In Pakistan it is mostly grown in arid and semi-arid areas of Punjab and Sindh.
Its seed is oval shaped dicotyledonous having diameter about 8mm. Its seed consists of hull germ. Relative composition of grain comprised of 14-17 per cent hull, 43-47 per cent germ and 34-36 per cent endosperm.
Due to rich source of galactomannan its grains are processed for extracting gum commonly known as guar gum or guaran. The production processes involve harvesting and drying of guar beans following growing season. First of all beans are shelled from pods to remove germ and hull. So two halves of seed are obtained from each seed and are known as dehusked guar splits. The guar splits are then grounded to powder form; this powder is then graded by quality and used for variety of purposes.
Finally finished guar gum powder is white to creamy colored and is nearly odorless. Depending upon industrial application different guar gum powder grades is manufactured. Grading is done on the basis of active matter content, granulation, viscosity, ph and degree of substitution.
Chemically guar gum is polysaccharide, a long chain made of sugars galactose and mannose. Due to its unique properties guar gum found its easy way than locust bean gum. It is easily soluble in both cold and hot water, fine film forming, resistant to oils and greases; better thickener and stabilizer properties increased its popularity. In food industry guar gum is used as thickening, gelling, stabilization, emulsification and binding agent. In food industries it is used in ice creams, soft drinks, chocolate milk, jams, jellies, bread, biscuits, soft cheese, ketchup, sauce and dressings.
In pharmaceutical industries used as thickening, suspension, water retention, gelling agent. In tablet manufacturing it is used as binder and disintegrating agent and also in micro-encapsulation of drugs. Guar gum is fibrous in nature as fiber contents is important part of food that play important role in proper functioning of intestine. World market of guar gum hover around 2-2.5 lakh tons annually. India is major producer in guar and guar gum in global market. It alone contributes 80 per cent of world total production followed by Pakistan and USA. Major importing countries are Canada, China, Chile, Australia, Austria, Brazil, Germany and others. The demand of guar gum largely depends upon petroleum in US and oil fields in Middle East and this demand is increasing due to increasing consumption pattern of petroleum.
Though climatic and soil requirement for its cultivation is much suitable in Pakistan but its production is low compared to that in India and other countries. Guar plant does well under warm and dry weather conditions. In Punjab, it is grown in dry and sandy regions of Bahawalpur and Thal while in Sindh it is cultivated in Khairpur, Nawabshah, Thatta and Tharparkar. Guar plant can grow in all types of soils but for healthy production it requires well drained, medium to light soils.
Guar is leguminous crop so instead of depleting soil as other crops do, increase soil nitrogen status of soil through biological nitrogen process. This fixed nitrogen then available to next crop. As climatic and soil conditions are suitable for this cash crop. So government should focus for exploration of full potentional of white gold powder and research organization should develop new high yielding varieties to meet ever increasing demand of guar gum powder. By giving awareness about this crop we can increase foreign earning. This crop should not be ignores and should be promoted like cereals and fibers crops.
The writers are associated with the Department of Agronomy, University of Agriculture, Faisalabad, Pakistan.