| Guar gum | |
|---|---|
| Identifiers | |
| CAS number | 9000-30-0 |
| Properties | |
| Acidity (pKa) | 5-7 |
| Hazards | |
| MSDS | MSDS |
| (verify) (what is: /?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) |
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| Infobox references | |
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 |
Guar gum is an extract of 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.
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]
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.
Guar gum is more soluble than locust bean gum and is a better stabilizer, 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 1% concentration, 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]
Guar gum is economical because it has almost eight 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 multiphase 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.
Guar gum retards ice crystal growth nonspecifically by slowing mass transfer across the solid/liquid interface. It shows good stability during freeze-thaw cycles.[5]
Manufacturers define different grades and qualities of guar gum by the particle size, the viscosity 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]
Modified forms of guar gum that are available commercially include enzyme-modified, cationic and hydropropyl guar.[8]
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.[10] In Europe, guar gum has EU food additive code E412.
Applications include:
Guar gum is a water-soluble fiber that acts as a bulk forming laxative, and as such, it is claimed to be effective in promoting regular bowel movements and relieve constipation and chronic related functional bowel ailments, such as diverticulosis, Crohn's disease, colitis and irritable bowel syndrome, among others. The increased mass in the intestines stimulates the movement of waste and toxins from the system, which is particularly helpful for good colon health, because it speeds the removal of waste and bacteria from the bowel and colon.
Several studies have found significant decreases in human serum cholesterol levels following guar gum ingestion. These decreases are thought to be a function of its high soluble fiber content.
Guar gum has been considered of interest in regard to both weight loss and diabetic diets. It is a thermogenic substance.[12] Moreover, its low digestibility lends its use in recipes as a filler, which can help to provide satiety, or slow the digestion of a meal, thus lowering the glycemic index of that meal. In the late 1980s, guar gum was used and heavily promoted in several weight-loss products. The U.S. Food and Drug Administration eventually recalled these due to reports of esophageal blockage from insufficient fluid intake, after one brand alone caused at least 10 users to be hospitalized, and a death.[13] For this reason, guar gum is no longer approved for use in over-the-counter weight loss aids in the United States. Moreover, a meta-analysis that combined the results of 11 randomized, controlled trials found guar gum supplements were not effective in reducing body weight.[14]
Two Japanese studies using rats showed guar gum supports increased absorption of calcium occurring in the colon instead of in the small intestine. This means lesser amounts of calcium may be consumed to obtain its recommended minimum daily intake (RDI). This has obvious implications for reduced calorie diets, since some calcium-rich dairy products tend to be high in calories.
However, guar gum is also capable of reducing the absorbability of dietary minerals (other than calcium), when foods or nutritional supplements containing them are consumed concomitantly with it. However, this is less of a concern with guar gum than with various insoluble dietary fibers.
Some studies have found guar gum to improve dietary glucose tolerance.[15] Research has revealed the water-soluble fiber in it may help people with diabetes by slowing the absorption of sugars by the small intestine. Although the rate of absorption is reduced, the amount of sugar absorbed is the same overall. This helps diabetic patients by lowering the amount of insulin needed to keep the blood glucose at a normal level.
It also functions as an adjuvant for diabetic drugs that are sometimes employed for the treatment of noninsulin dependent diabetes. The effect is to help lower blood glucose levels. Thus, diabetic patients who are taking drugs should consult their doctors before supplementing with guar gum.