What Is Guar Gum?

Guar gum is obtained from the seed of the guar plant, Cyanaposis tetragonolobus, in the Leguminosae family, and has the general structure of galactomannans.

The Plant

The plant Cyanaposis tetragonolobus has been grown in Pakistan and India for hundreds of years and is an important food crop for humans and animals. The crop is also grown in the hotter states of the USA.  The guar plant is a pod-bearing, nitrogen-fixing legume. The seeds of the plant are composed of the hull (15%), germ (45%), and endosperm (40%). It is an annual that is ideal for arid and semi-arid regions of the world. Production of guar has been highly variable because of the annual nature of the plant, mainly through variable weather conditions. The southern hemisphere countries are now growing guar plants to cover the seasons.

Production Of Guar

Guar gum is produced by milling the endosperm after removal of the hull and germ. Generally, the guar seeds are milled to split them (guar splits) and remove the hull; the guar splits are then hydrated and milled to a powder. The milled powder fractions are blended to meet commercial specifications, particularly particle size distribution and viscosity. Purity is important as gum products may contain residual hull and germ; hence protein content and acid insoluble residue (an indication of the residual hull content) are also specified. The very simple production process makes guar gum an ideal candidate for natural hydrocolloid status.

Structure and Composition of Guar Gum

A typical analysis of gum guar is mainly galactomannan 78–82%, moisture 10–15%, protein 4–5%, crude fibre 1.5–2.5%, and ash 0.5–0.9%.

Guar is a linear, substituted, neutral polysaccharide. It consists of a main chain (1→4) β-D-mannopyranosyl (D-mannose) units substituted at O-6 by single-unit side-chains of α-D-galactopyranose (D-galactose). The main linkages are  thus 1,4-β-glycosidic linkages with 1,6-linkages for the side chains.

The ratio of mannose to galactose is approximately 1.6:1 to 2:1, depending on the source and method of extraction used to isolate the gum.

Properties Of Guar Gum

Guar gum forms viscous colloidal solutions when hydrated in cold water systems. These solutions show the typical variance of viscosity versus shear rate of non-Newtonian fluids. Viscosities of 0.3% w/w solutions change only slightly with increasing shear rates, while solutions of 1% w/w or greater show marked changes. Viscosity is dependent on time, temperature, concentration, pH, ionic strength, and the type of agitation as well. The hydration and water-binding properties of guar gum are responsible for its food stabilising systems.

Applications For Guar Gum

The food industry is the largest market for gums such as guar and xanthan gum. Applications cover ice pops, ice lollies, yogurts, sherbets and various beverages. It is one of the cheapest gums available compared to others like gellan gum (Nieto, 2009). 

Guar gum has excellent freeze-thaw stability. Ice cream stabilisation, particularly those products relaying on high temperature, short-time processes, use guar gum at a concentration of 0.3%. The gum improves body, texture, chewiness, and heat-shock resistance by binding free water present. 

Guar is allowed at levels up to 3.0% in cold-pack cheese foods; the gum helps to eliminate syneresis and weeping. In soft cheeses, guar increases the yield of curd solids and gives curd a better texture. Pasteurised process cheese spreads use a stabiliser consisting of guar, locust bean gum, and emulsifier at 0.25–0.35% of total weight. 

Guar may be added to dough to retard dry-out; it is useful in cake and doughnut mixes at levels under 1%. In pie fillings, guar gum thickens and prevents shrinking and cracking of the filling. Used in icings to absorb free water, guar gum is mixed at a level of one part gum to 250 parts of sugar and 30 parts water; this prevents the icing from becoming sticky and adhering to the wrapper.

Guar has been used as a thickener in salad dressings and pickle and relish sauces at 0.2–0.8%; tragacanth, however, is superior in these applications since gum guar will break down more readily at low pH levels. Gum guar, however, is used to great advantage in meat sauces and gravies; this use allows a significant reduction in the solids content of the product.

Gum guar alone or in combination with agar at levels of 0.5% is useful in processing canned meat products; it prevents fat migration during storage, stops syneresis and water accumulation. It also reduces the tendency for voids to be present in the can.

Gum guar has good mouth feel and adds body and texture to improve thin or watery products such as low juice or low sugar beverages. It is commonly used in dietetic beverages where sugar is absent. In addition, blends of guar gum and carrageenan are used in cocoa beverages as well as chocolate syrups. Guar gum is a versatile and effective suspending agent.

The gum is used to make edible films. One example it was used to coat french fries with sorbitol incorporated into the film (Jia et al., 2017). It works well with other carbohydrates such as potato starch (Nandi & Guha, 2018).  

Dietary Fiber Source

Health Canada has approved partially hydrolyzed guar gum for use as a dietary fiber source. The fibre is produced by Taiyo International and is known as Sunfiber. It is a soluble, transparent, and tasteless dietary fiber. 

Sunfiber is a galactomannan-based fiber as opposed to a sugar/starch based fiber that allows product formulators to bring the benefits of this truly regulating fiber to consumers who are looking for a unique, more comfortable fiber source,” claims Taiyo’s Vice President Lekh Juneja.

Sunfiber is low in viscosity, improves stability of beverages at various pH levels, and is resistant to heat, acid, and digestive enzymes. In addition to its blood glucose benefits, Sunfiber improves absorption of minerals (such as calcium, iron, and zinc) and aids protein utilization. Sunfiber has prebiotic characteristics that stimulate health-promoting indigenous bacteria such as Lactobacilli and Bifidobacteria.

Labelling

In the EU, it has the food additive number E412.

Reference

Dea, I.C.M., Morrison, A. (1975) Chemistry and interactions of seed galactomannans. Adv. Carbohydr. Chem. Biochem. 32 pp. 241–312

Featherstone, S. (2015) Chapt. 8 – Ingredients used in the preparation of canned foods. In: A Complete Course in Canning and Related Processes (Fourteenth Edition). Volume 2: Microbiology, Packaging, HACCP and Ingredients.  Woodhead Publishing Pages 147-211

Jia, B., Fan, D., Li, J., Duan, Z., & Fan, L. (2017). Effect of guar gum with sorbitol coating on the properties and oil absorption of French fries. International Journal of Molecular Sciences, 18(12), pp. 2700 (Article).

Nandi, S., & Guha, P. (2018). Modelling the effect of guar gum on physical, optical, barrier and mechanical properties of potato starch based composite film. Carbohydrate Polymers, 200, pp. 498–507 (Article). 

Nieto, M. B. (2009). Structure and function of polysaccharide gum-based edible films and coatings. In: M. E. Embuscado & K. C. Huber (Eds.), Edible films and coatings for food applications (pp. 57–112). New York, NY: Springer. (Article)