Guar gum, also called guaran, is a galactomannan. It is primarily the ground endosperm of guar beans. The guar seeds are dehusked, milled and screened to obtain the guar gum.^[1] It is typically produced as a free flowing, pale, off-white colored, coarse to fine ground powder.

Contents 1 Production 2 Trade 3 Properties 3.1 Chemical composition 3.2 Solubility and viscosity 3.3 Thickening 3.4 Ice-crystal growth 4 Grading 5 Industrial applications 6 Food applications 7 Nutritional and medicinal effects 8 References

Production

Guar gum is extracted from the guar bean, where it acts as a food and water store. The guar bean is principally grown in India and Pakistan, with smaller crops grown in the U.S., Australia, China, and Africa. The drought-resistant guar bean can be eaten as a green bean, fed to cattle, or used in green manure.

Trade

According to a Reuters report, India accounts for about 80 percent of the global trade in guar products.^[2][3]. India exported 11 billion rupees worth of guar products in 2007/08 financial year ending March 2008. Pakistan trails India in the global trade. Industrial guar gum is the most sought after guar product, and accounts for about 45 percent of the total demand. Industrial gum is used as a controlling agent in oil wells to facilitate easy drilling and prevent fluid loss.^[4]

In 2007, the Indian industry was hit by a contamination crisis when the European Union suspended imports of Indian guar gum after excessive levels of dioxins were found in one shipment^[3].

Properties

Chemical composition

Chemically, guar gum is a 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.

Solubility and viscosity

Guar gum is more soluble than locust bean gum and is a better emulsifier as it has more galactose branch points. Unlike locust bean gum, it is not self-gelling.^[5] However, 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 pH extremes at temperature (e.g. pH 3 at 50°C).^[5] 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.

Guar gum shows high low-shear viscosity but is strongly shear-thinning. It is very thixotropic above concentration 1%, but below 0.3% the thixotropy is slight. It has much greater low-shear viscosity than that of locust bean gum, and also generally greater than that of other hydrocolloids. Guar gum shows viscosity synergy with xanthan gum. Guar gum and micellar casein mixtures can be slightly thixotropic if a biphase system forms.^[5][6]

Thickening

Guar gum is economical because it has almost 8 times the water-thickening potency of cornstarch - only a very small quantity is needed for producing sufficient viscosity. Thus it can be used in various multi-phase formulations: as an emulsifier because it helps to prevent oil droplets from coalescing, and/or as a stabilizer because it helps to prevent solid particles from settling.

Ice-crystal growth

Guar gum retards ice crystal growth non-specifically by slowing mass transfer across the solid/liquid interface. It shows good stability during freeze-thaw cycles.^[5]

Grading

Manufacturers define different grades and qualities of guar gum by the particle size, the viscosity that is generated with a given concentration, and the rate at which that viscosity develops. Coarse-mesh guar gums, will typically — but not always — develop viscosity more slowly. They may achieve a reasonably high viscosity, but will take longer to achieve. On the other hand, they will disperse better than fine-mesh, all conditions being equal. A finer mesh, like a 200 mesh, requires more effort to dissolve.^[7]

Industrial applications

• Textile industry – sizing, finishing and printing
• Paper industry – improved sheet formation, folding and denser surface for printing
• Explosives industry – as waterproofing agent mixed with ammonium nitrate, nitroglycerin etc.
• Pharmaceutical industry – as binder or as disintegrator in tablets
• Cosmetics and toiletries industries – thickener in toothpastes, conditioner in shampoos (usually in a chemically modified version)
• Oil and gas drilling, hydraulic fracturing
• Mining
• Hydroseeding – formation of seed bearing "guar tack"^[8]

Food applications

The largest market for guar gum is in the food industry. In the U.S., differing percentages are set for its allowable concentration in various food applications.^[9] In Europe, guar gum has EU food additive code E412.

Applications include:

• Baked goods - increases dough yield, gives greater resiliency, and improves texture and shelf life; in pastry fillings, it prevents "weeping" (syneresis) of the water in the filling, keeping the pastry crust crisp.^[10]

• Dairy - thickens milk, yogurt, kefir, and liquid cheese products; helps maintain homogeneity and texture of ice creams and sherbets

• Meat - functions as lubricant and binder.

• Dressing and sauces - improves the stability and appearance of salad dressings, barbecue sauces, relishes, ketchups and others

• Misc. - Dry soups, instant oatmeal, sweet desserts, canned fish in sauce, frozen food items and animal feed.

Source: Wikipedia