Gomme de guar

Guar gum, also called guaran, is a galactomannan polysaccharide extracted from guar beans that has thickening and stabilizing properties useful in food, feed, and industrial applications. The guar seeds are mechanically dehusked, hydrated, milled and screened according to application. It is typically produced as a free-flowing, off-white powder. The guar bean is principally grown in India, Pakistan, the United States, Australia and Africa. India is the largest producer, accounting for nearly 80% of the world production. In India, Rajasthan, Gujarat, and Haryana are the main producing regions. The US has produced 4,600 to 14,000 tonnes of guar over the last 5 years. Texas acreage since 1999 has fluctuated from about 7,000 to 50,000 acres. The world production for guar gum and its derivatives is about 1.0 million tonnes. Non-food guar gum accounts for about 40% of the total demand. Chemically, guar gum is an exo-polysaccharide composed of the sugars galactose and mannose. The backbone is a linear chain of β 1,4-linked mannose residues to which galactose residues are 1,6-linked at every second mannose, forming short side-branches. Guar gum has the ability to withstand temperatures of 80 °C (176 °F) for five minutes. Guar gum is more soluble than locust bean gum due to its extra galactose branch points. Unlike locust bean gum, it is not self-gelling. Either borax or calcium can cross-link guar gum, causing it to gel. In water, it is nonionic and hydrocolloidal. It is not affected by ionic strength or pH, but will degrade at extreme pH and temperature (e.g. pH 3 at 50 °C). It remains stable in solution over pH range 5–7. Strong acids cause hydrolysis and loss of viscosity and alkalies in strong concentration also tend to reduce viscosity. It is insoluble in most hydrocarbon solvents. The viscosity attained is dependent on time, temperature, concentration, pH, rate of agitation and particle size of the powdered gum used. The lower the temperature, the lower the rate at which viscosity increases, and the lower the final viscosity.