|Guar bean cluster|
Cyamopsis psoralioides L.
The origin of Cyamopsis tetragonoloba is unknown, since it has never been found in the wild. It is assumed to have developed from the African species C. senegalesis. It was further domesticated in India and Pakistan, where it has been cultivated for many centuries. Guar grows well in arid to semiarid areas, but frequent rainfall is necessary. This legume is a very valuable plant within a crop rotation cycle, as it lives in symbiosis with nitrogen-fixing bacteria. In fact, agriculturists in semi-arid regions of Rajasthan follow crop-rotation and use guar as a source to replenish the soil with essential fertilizers and nitrogen fixation, before the next crop. Guar as a plant has a multitude of different functions for human and animal nutrition but its gelling agent containing seeds (guar gum) are today the most important use. Demand is rising rapidly due to industrial use of guar gum in hydraulic fracturing (oil shale gas). About 80% of world production occurs in India and Pakistan, but, due to strong demand, the plant is being introduced into new areas.
Cyamopsis tetragonoloba grows upright, reaching a maximum height of up to 2–3 m. It has a main single stem with either basal branching or fine branching along the stem. Thanks to taproots, the guar plant can access soil moisture in low soil depths. Additionally, this legume develops root nodules with nitrogen-fixing soil bacteria rhizobia in the surface part of its rooting system. Its leaves and stems are mostly hairy, dependent on the cultivar. Its fine leaves have an elongated oval shape (5 to 10 cm length) and of alternate position. Clusters of flowers grow in the plant axil and are of white to blueish color. The developing pods are rather flat and slim containing 5 to 12 small oval seeds of 5 mm length (TGW = 25-40 g). Usually, mature seeds are white or gray, but in case of excess moisture they can turn black and lose germination capacity. The chromosome number of guar seeds is 2n=14. The seeds of guar beans have a very remarkable characteristic. Its kernel consists of a protein-rich germ (43-46%) and a relatively large endosperm (34-40 %), containing big amounts of the galactomannan. The latter is polysaccharide containing polymers of mannose and galactose in a ratio of 2:1 with many branches. Thanks to the latter, it exhibits a great hydrogen bonding activity  having a viscosifying effect in liquids.
Guar is very drought-tolerant and sun-loving, but it is very susceptible to frost. Even though it can cope with little but regular rainfall, it requires sufficient soil moisture before planting and during maturation of seeds. Frequent drought periods can lead to delayed maturation. On the contrary, too much moisture during early phase of growth and after maturation lead to lower seed quality.
Cyamopsis tetragonoloba (L.) can grow on a wide range of different soil types. Preferably in fertile, medium-textured and sandy loam soils that are well-drained because waterlogging decreases plant performance. In respect of soil acidity, guar grows best in moderate alkaline conditions (pH 7-8) and is tolerant of salinity. Thanks to its taproots which are inoculated with rhizobia nodules, it produces nitrogen-rich biomass and improves soil quality.
|Harvest||seed pods: dry, brown, 60–90 days after sowing; biomass: first lower pods turn brown|
|Yield||seeds: 5-8 dt/ha; biomass: 40-50 t/ha|
It is grown principally in north-western India and Pakistan with smaller crops grown in the semiarid areas of the high plains of Texas in the USA, Australia and Africa. The most important growing area centres on Jodhpur in Rajasthan, India where demand for guar for fractionation produced an agricultural boom as in 2012. Currently, India and Pakistan are the main producers of cluster bean, accounting for 80% production of the world's total, while Thar, Punjab Dry Areas in Pakistan and Rajasthan occupies the largest area (82.1%) under guar cultivation in India. In addition to its cultivation in India and Pakistan, the crop is also grown as a cash crop in other parts of the world. Several commercial growers have converted their crops to guar production to support the increasing demand for guar and other organic crops  in the United States.
Pusa Naubahar and Pusa Sadabahar. Seeds at the rate of 30 kilograms/hectare (9–11 lb/acre) are planted at a spacing of 45-60 x 20–30 cm (18–24 x 8–12 in) in February–March and June–July. During rainy season, the seeds are sown 2–3 cm (~1 in) deep on ridges and in furrows during summer months. FYM is applied at the rate of 25 tonnes/ha (11.1 tons/acre). N, P2O5 and K2O recommendation for the crop is 20:60:80 kg/ha (18:53:71 lb/acre). Average yield is 5 to 6 tonnes/ha (2.2–2.6 tons/acre). Meager information is available for genetic variability in clusterbean addressing the qualitative traits (Pathak et al. 2011)
- Forage: Guar plants can be used as cattle feed, but due to hydrocyanic acid in its beans, only mature beans can be used.
- Green manure: Guar plantings increase the yield of subsequent crops as this legume conserves soil nutrient content.
- Vegetable: Guar leaves can be used like spinach and the pods are prepared like salad or vegetables. Its beans are very nutritious but the guar protein is not usable by humans unless toasted to destroy the trypsin inhibitor.
As mentioned in the biology part of this entry, the seeds of the guar bean contain a very big endosperm. This endosperm consists of a very big polysaccharide of galactose and mannose. This polymer is water soluble and exhibits a viscosifying effect in water. Guar gum has a multitude of different applications:
- Food: In several food and beverages guar gum is used as additive in order to change its viscosity or as fiber source.
|Baked goods||Dough improver |
|Cheese||Texture improver |
|Ice Cream||Smaller ice crystals |
|Fried Products||Oil uptake reduction |
Partially hydrolyzed guar gum (PHGG) is produced by the partial enzymatic hydrolysis of guaran, the galactomannan of the endosperm of guar seeds (guar gum). It is a neutral polysaccharide consisting of a mannose backbone chain with single galactose side units occurring on almost two out of every three mannose units. The average molecular weight is about 25,000 Daltons. This gives a PHGG that still assays and functions as a soluble dietary fiber. PHGG as sold commercially is completely soluble, acid and heat stable, unaffected by ions, and will not gel at high concentrations. Commercial PHGG is approximately 75% dietary fiber and has minimal effect on taste and texture in food and beverage items. PHGG is fully fermentable in the large bowel, with a high rate of volatile fatty acid formation. The pH of the feces is lowered along with an increase in fecal bulk that mainly consists of bacterial cell mass and water. Clinical studies have demonstrated a prebiotic effect of PHGG. Studies have also shown that PHGG can be used to maintain regularity. PHGG is used in foods for particulate suspension, emulsification, antistaling, ice crystal control, and reduced fat baked goods.
Derivatives of guar gum that has been further reacted is also used in industrial applications, such as the paper and textile industry, ore flotation, the manufacture of explosives and hydraulic fracturing (fracking) of oil and gas formations. Guar gum is often crosslinked with boron or chromium ions to make it more stable and heat-resistant. The crosslinking of guar with metal ions results in a gel that does not block the formation and helps efficiently in formation cleaning process. Guar and its derivatives make gel complexes with ions of Aluminium, Zirconium,Titanium, Chromium and Boron. The borate–guar reaction is reversible, and depends on the pH (hydrogen ion concentration) of the solution. Crosslinking of guar with borate occurs at high pH (approximately 9–10) of the solution. Guar gum has also proven a useful substitute for locust bean gum (made from carob seeds).
Through the use of guar gum in the extraction of oil and shale gas, the demand has increased a lot. Only 10% of the Indian production stays within the country and another 90% of the exports are used for shale gas and oil industries. Consequently, many former cotton or wheat fields are converted into guar fields as production costs are also lower. But the increase of guar gum prices has also other reasons.
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- "large scale guar growers"
- "organic fertilizer crops"
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