Also known as E412, Cluster bean, Cyamopsis tetragonoloba and Guaran.
Guar is a coarse, upright, bushy annual plant, ranging from 2 - 9 feet in height. It has pointed, saw-toothed, trifoliate leaves and hairy pods 3 - 4 inches long in clusters. Guar flowers are self-pollinating. A mature, unopened bud starts out white, changes to a light pink as petals begin to open and finally, the flower turns deep blue-purple. Guar is also called ‘cluster bean’ because of the manner in which its pods are clustered together.
Guar is a native plant of India (where the young beans are used as a vegetable and livestock feed, as well as for producing guar gum), and was introduced into the United States from India in 1903. Commercial production of guar in the United States began in the early 1950s, and has been concentrated in northern Texas, Arizona and southwestern Oklahoma, but it has also adapted to locations with more tropical climates, such as in Florida and Puerto Rico. The major world suppliers are India, Pakistan and the United States, with smaller acreages in Australia and Africa.
In the early 1980s, Texas growers were planting about 100,000 acres annually. They harvested about half of the planted acreage and ploughed the rest under as green manure. Like other legumes, guar is an excellent soil-building crop – the root nodules contain nitrogen-fixing bacteria, and crop residues, when ploughed under, improve yields of succeeding crops.
Guar gum is a polysaccharide, and is extracted from the ground endosperm of the seed of the shrub. It is similar to locust bean gum, and is made up of non-ionic polydisperse rod-shaped polymers consisting of molecules of about 10,000 residues. It contains about 80% galactomannan, 12% water, 5% protein, 2% acid insoluble ash, 0.7% ash and 0.7% fat.
Guar gum is used as a binder (up to 10%) and disintegrating agent in solid dosage forms. It is also used as a suspending, thickening and stabilising agent (up to 2.5%) in liquid oral and topical pharmaceutical and cosmetic products. In the food industry, guar gum is an economical thickener and stabiliser, and has almost eight times the thickening power of cornstarch. It is used in sauces, dressings and baking mixes.
The gum is also used in paper manufacturing, textiles, and printing. Guar gum is more soluble than locust bean gum, and a better emulsifier, as it has more galactose branch points. Unlike locust bean gum, it does not form gels, but does show good stability to freezing and thawing cycles. Being non-ionic, it is not affected by ionic strength or pH, but will degrade at pH extremes at temperature (e.g. pH 3 at 50°C). Guar gum retards ice crystal growth non-specifically by slowing mass transfer across solid/liquid interface.
Guar gum hydrates and swells quite rapidly in cold water to give highly viscous pseudo-plastic solutions. This gelling retards the drug release from tablets, and consequently, guar gum is used to deliver drugs to the colon. Guar gum helps regulate the rate of absorption of nutrients, including sugar, spreading it over a longer period of time. This results in a slower rise in blood sugar levels, and a less rapid drop.
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