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.
Production and trade
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.
Properties
Chemical composition
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.
Solubility and viscosity
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. Above 80°, the final viscosity is slightly reduced. Finer guar powders swell more rapidly than larger particle size coarse powdered gum.
Guar gum shows a clear low shear plateau on the flow curve and is strongly shear-thinning. The rheology of guar gum is typical for a random coil polymer. It does not show the very high low shear plateau viscosities seen with more rigid polymer chains such as xanthan gum. It is very thixotropic above 1% concentration, but below 0.3%, the thixotropy is slight. Guar gum shows viscosity synergy with xanthan gum. Guar gum and micellar casein mixtures can be slightly thixotropic if a biphase system forms.
Thickening
One use of guar gum is a thickening agent in foods and medicines for humans and animals. Because it is gluten-free, it is used as an additive to replace wheat flour in baked goods.:41 It has been shown to reduce serum cholesterol and lower blood glucose levels.
Guar gum is also economical because it has almost eight times the water-thickening ability of other agents (e.g. cornstarch) and only a small quantity is needed for producing sufficient viscosity. Because less is required, costs are reduced.
In addition to guar gum's effects on viscosity, its high ability to flow, or deform, gives it favorable rheological properties. It forms breakable gels when cross-linked with boron. It is used in various multi-phase formulations for hydraulic fracturing, in some as an emulsifier because it helps prevent oil droplets from coalescing, and in others as a stabilizer to help prevent solid particles from settling and/or separating.