Elsevier

Carbohydrate Polymers

Volume 199, 1 November 2018, Pages 534-545
Carbohydrate Polymers

Review
Guar gum and its composites as potential materials for diverse applications: A review

https://doi.org/10.1016/j.carbpol.2018.07.053Get rights and content

Highlights

  • Guar gum; one of the cheapest sources of galactomannan.

  • Molecular structure and properties of guar gum are presented.

  • Guar gum is useful in various industries; food, cosmetics, explosive, textile and oil refinery etc.

  • Various types of guar gum composites are presented.

  • Potential applications of guar gum composites are discussed.

Abstract

Naturally occurring polymers are currently of prime importance among which polysaccharides occupies superior position due to their easy availability, eco- friendly and non-toxic nature. Guar gum, one of the naturally occurring polymer, is a galactomannan acquired by ground endosperm of Cyamopsis tetragonolobus or Cyamopsis psoraloides. It belongs to the family leguminosae. Presence of large number of hydroxyl groups increases its H- bonding ability when dissolved in water that enhance the viscosity and gelling properties of the guar gum solution. Based upon these properties, guar gum is used in several industries such as textile, food, petrochemical, mining and paper for varied applications. It is used as suspending, emulsifying, gelling and stabilising agent in the conventional dosage forms.

Last few decades have marked the increase in development of various composites of guar gum that have intrinsic utilization in various fields. Immobilization of guar gum with the others not only enhances its properties but also enriches its utilization in numerous fields for diverse applications such as water purification, drug delivery, pharmaceutical, cosmetic and food industries, etc. Guar gum derivatives are found to have therapeutic importance in certain physiological disorders also. In this review article, we have summarized various possible composites of guar gum and their most probable applications in different fields.

Introduction

Polysaccharides are chemical compounds connected through glycosidic bonds to form highly complex structures utilized widely for diverse applications. Polysaccharides can be categorized on the basis of their source of origin (natural or synthetic), hydrophilicity (hydrophobic or hydrophilic) and molecular weight (low or high) etc. With growing interest towards bio- degradable, renewable, biocompatible and non- toxic material synthesis, more stress has been laid on the use of natural polysaccharides. In addition to biodegradable nature, naturally occurring polysaccharides are stable, cheap and easily available. Natural polysaccharides such as glycogen and chitin are present in animals, however, cellulose and starch are present in human being where they act as the energy storage agents. Presence of unique functionalities in their structure offers them the ability to exhibit various properties that can be used for a wide range of applications such as food processing, drug delivery, water purification and cosmetic production (Tosco et al., 2014). In addition to these, polysaccharides have been used as thickeners, emulsifiers and wound- healing agents. Large number of polysaccharide derivatives can also be produced due to the presence of functional groups which allows for facile modification either chemically or biochemically. Naturally occurring polysaccharides have high affinity to bind to a number of complex structures through covalent bonding due to the presence of highly reactive groups such as hydroxyl, carboxyl and amino groups.

One of the category of polysaccharides; natural gums is extensively employed for enhancing the viscosity of solution even in their diminishing low concentrations. Natural gums are hydrophobic compounds derived chiefly from plant or microbial sources. Being of biological origin, the gum molecules display remarkable discrepancy in the linear chain length, branching features and molecular weight, etc. On hydrolysis, natural gums form mixture of xylose, arabinose, galactose, mannose and uronic acids, etc. Based on the source of origin, gums are classified into (a) plant exudate gum (including gum karaya, salai gum and gum arabic), (b) seed gum (includinng guar gum, locust bean gum and tamarind gum), (c) microbial gum (which comprises of xanthan gum, gellan gum and dextran gum) and (d) marine gums (e.g. aliginic acids). Exudate gums are formed gummosis process involving the disintegration of plant cellulose and seed gums are attained from the seed embryos. However, microbial gums are produced by some special microorganisms by fermentation processes and marine gums are found either as the cell walls of various algae or deposited in intracellular regions as reserve food materials. Starch, cellulose, galactomannan, sodium alginate, xanthan gum, dextran, carrageenan and hyaluronic acids are some of the commonly used and commercially important natural polysaccharides (Thombare et al., 2016).

Among these polysaccharides, galactomannan is the most frequently used polysaccharide. Galactomannan are the linear polysaccharides consisting of mannose backbone onto which the galactose units are linked as side chains. They display an extensive array of novel and commercially valuable properties. The physical properties of galactomannans strongly depend upon the average galactose content. Strong synergistic interactions with biopolymers can be observed with lower galactose content. Chief sources of galactomannan include locust bean, tara, cassia and guar. Among these sources, guar gum is easily available and the cheapest source; hence it is primarily investigated by a number of researchers as a source of galactomannan.

Guar gum is one of the cheapest sources of galactomannan, obtained from the endosperm of Cyamopsis tetragonolobus or Cyamopsis psoraloides. It belongs to the family leguminosae. Also known as Glucotard, Guaran, Cluster bean, Cyamopsis, Cuarina and Calcutta lucern. Guar gum is a high molecular weight polysaccharide with white to yellowish white appearance and odourless acquired from the guar plant. The guar plant is of few meters usually about 0.6 m with pods of 5–12.5 cm length (Thombare et al., 2016). Guar gum in plants acts as a food reserve for the embryo during the time of germination. It is usually found in the Indian subcontinents, southern hemisphere in semi-arid zones of Brazil, South Africa, and Australia or in the southern part of USA, like Texas or Arizona. A total 90% of guar is produced by India and Pakistan only out of which 80% is manufactured by India only. In the year 2013-14, approximately 650 thousand tons of guar gum was manufactured in India, out of which 601 thousand tons was traded, more than 50% of which was exported to USA. Hydrocarbons, fats, alcohols, esters and ketones do not dissolve the guar gum but with few exceptions (e.g. formamide) in organic solvents. The only important solvent for guar gum is water (Poorna et al., 2016).

Guar gums constitute the example of hydrophilic polysaccharides. They have a rod like polymeric structure in which galactose side chains are linked on the mannose backbone with an average molecular ratio of 1:2. Straight chains of D-mannose units are linked together by β (1–4) glycoside linkage and D-galactose units are joined in alternate manner through (1–6) glycoside linkage. Hydroxyl groups present in the polymeric structure help in the manufacturing of various derivatives utilized for various industrial applications. Fig. 1 shows the structure of guar gum and the overall chemical composition of guar gum with their relative percentage has been presented in Table 1 (Mcclendon et al., 1976). Structure and chemistry of guar gum can be determined using various techniques such as chemical tests (acid hydrolysis, methylation and formation of tolyl sulphonyl-derivative), analytical tests (chromatography, scanning electron microscopy, nuclear magnetic resonance, R- ray diffraction and Infra- red spectroscopy), biological test (selective enzyme hydrolysis) and physical tests (optical rotation, stress-strain measurement and X-ray analysis) (Daas et al., 2000; Parashar et al., 1993). It is actually the naturally occurring water soluble polysaccharide with the highest molecular weight naturally. Its properties mainly depend upon the chemical features like chain length, abundance of cis−OH groups, steric hindrances, degree of polymerization and presence of substituents, etc. Advanced techniques have concluded that the number average molecular weight of guar gum lies in the range of 106 to 2 × 106 g/mol.

Guar gum has unique and interesting physical properties. It is usually insoluble in hydrocarbons, fats, alcohols, esters and ketones. Guar gum shows high solubility in water only. In water surroundings, galactose units present on mannose units interact with the water molecules and results into inter- molecular chain entanglement that helps in thickening and increasing viscosity of the solution. Aqueous dispersion of even 1% of good quality guar gum may increase the viscosity to room temperature to as high as 10,000 cP. Guar gum results in viscous colloidal solution when dispersed in hot and cold water even in very minute amounts. Guar gum can attain its full viscosity in cold water while other gums acquire the same viscosity after prolonged heating. Concentration, dispersion, pH, temperature and presence of foreign substances are the most influencing variables responsible for affecting the viscosity and hydration rate of guar gum (Pathania, Katwal, Sharma, et al., 2016). There exists a proportional relationship between the guar gum concentration and viscosity. Increase in concentration of guar gum enriches the inter-molecular chain interactions which increases the viscosity of solution. The most interesting feature of guar gum in solution form is its non- toxic nature over a wide range of pH, which arises from its stable and uncharged nature. pH usually do not affects the final viscosity of guar gums. The highest hydration rate is attained at pH 8–9 and lowest hydration rate occurs at pH > 10 and < 4. In addition to pH, temperature also influences the viscosity and hydration rate to a great extent. Generally, guar gum attains maximum viscosity at higher temperature as compared to lower temperatures. However, prolonged heating cause the water molecules to lose their ordering around the guar gum molecules as a result of which the conformation gets disturbed resulting in reduced viscosity (Tripathy et al., 2008; Zhang et al., 2005). Guar gum chains contain numerous hydroxyl groups that form hydrogen bonding in aqueous solution. In addition to the mannose chain structure of galactomannan, single membered galactose branches, increases the number of exposed hydroxyl groups. Due to the presence of these exposed hydroxyl groups, an unusual effect on the hydrated colloid system can be observed. It can form H- bonding with both hydrated mineral and organic surfaces due to which it affects most of the systems by its action. Due to this, the guar gum can be used as a dispersant for organic systems (having hydroxyl or carboxylic groups) and as a coagulant for inorganic ones (especially with clay characteristics). Guar gum behaves differently in the sugar and salt solutions. Presence of sugar molecules in the guar solution decreases the hydration, since the sugar molecules compete with the guar gum for hydration. Consequently, the solution viscosity decreases, which is inversely proportional to the sugar concentration. However, presence of salt does not affect the hydration rate of guar gum. Its presence even enhances the viscosity of the guar gum since the salts increases intermolecular interactions.

India is the major producer of total guar in the world. Guar gum is obtained by ground endosperm of Cyamopsis tetragonolobus. Number of mechanical processes utilized commercially in the extraction of guar gum from seeds which includes sieving, polishing, attrition and roasting, etc. Endosperm can be easily separated from its constituting components due to variation in the hardness of the components. After the separation of hull and germ, guar splits are obtained. The hull is very easy to separate after heat treatment by either attrition milling or various types of impact mills. The finer germ and hull fractions can be recovered from the endosperm easily by sieving. Then milling process is used to obtain powdered guar gum. The obtained guar gum is further purified by dissolution in water, precipitation and recovery with ethanol or isopropanol. It is called clarified (extracted or purified) guar gum. Clarified guar gum easily available in markets is normally standardized with sugars (Tripathy & Das, 2013). Large amount of water imbibed by the guar resulted in dispersion of high viscosity. Temperature has been found to be the influential factor on the basic properties of the guar gum (Kumar & Singh, 2018). Increase in temperature resulted in loss of water of hydration around the polymer molecules (Modasiya et al., 2010; Pal et al., 2015; Tripathy & Das, 2013). Guar gum processing has been presented in Fig. 2. Guar gum, being biocompatible shows varied properties such as rate of solubilization and viscosity from one solution conditions to another (Brassesco et al., 2017; Modasiya et al., 2010). Viscosity of the medium depends mainly upon impurities, pH and temperature etc based on which the grading of guar gum is done as food grade and industrial grade (Szopinski et al., 2015).

Guar gum finds limited use in original forms due to abandoned degree of viscosity and hydration. Its industrial applications such as in food, paint and pigments, oil field, mining, paper, water treatment, personal care, pharmaceutical and new types of superabsorbent enlarge by chemical modification that result into emergence of enhanced properties. Natural polysaccharides can easily be converted to carboxymethyl derivatives which offer the researchers a wide range of applications (Kamel et al., 2008). Some of the reported derivatives of guar gum are Hydroxymethyl guar gum (Lapasin et al., 1991), Hydroxypropyl guar gum (Lapasin, Lorenzi, Pricl, & Torriano, 1995) O-Carboyxymethyl-O-2-hydroxy-3-(trimethylammonia propyl) guar gum (CMHTPG) (Zhang et al., 2005), methacryloyl guar gum (Xiao & Dong, 2011) and Sulfated guar gum (Vismara et al., 2012) etc. The presence of hydroxyl groups in the guar gum makes them suitable for altering the structure formula and functionalization (Patel et al., 2014). Physical and chemical properties of the guar gum can be easily altered by various processes such as grafting, blending and compositing with synthetic and natural polymers (Dodi et al., 2011; Yi & Zhang, 2007).

Hydrogels are the highly crosslinked complex structures having high water absorbing ability. They have exceptionally enhanced hydrophilic abilities, high swelling ratio and biocompatible which make them applicable for use in a number of fields such as drug delivery, biosensors and agriculture etc. In hydrogels, polysaccharide chains get randomly tied to each other through cross- linkers such as methylene- bis- acrylamide, glutaraldehyde and derivatives of ethylene-glycol-di(meth)acrylate, etc. The active sites of the crosslinking agents undergo intermolecular bonding with hydroxyl groups of polymer chains to form highly compact coil like assembly (Brassesco et al., 2017; Sharma et al., 2017c). To such a compact structure, when water molecules are added, they get entrapped into it which results in high water adsorption and water holding tendency of the hydrogel system. A number of hydrogel systems based on guar gum have been fabricated as reported in literature. Hydrogels such as alginate/guar gum, xanthan/guar gum, aminated/guar gum, sage seed gum/guar gum, starch/guar gum and agarose/guar gum, etc have been reported in literature which are of immense importance. George and Abraham in 2007 have reported the use of novel alginate-guar gum based hydrogel for controlled delivery of protein drug. Alginate being a non- toxic polysaccharide with high pH sensitivity was crosslinked with guar gum. Alginate actually has properties for intestinal delivery of protein drugs. Results have showed that high pH, necessary for ion gelation, limits the practical use of hydrogel due to rapid dissolution of alginate and burst release of entrapped protein drug as it enters the intestine (Seeli & Prabaharan, 2017; Yi & Zhang, 2007). Maity and Ray in 2016 proposed the preparation of guar gum and nano sized bentonite clay in acrylic acid based hydrogel utilized for chromium removal from aqueous solution. High adsorption capacity of 182.4 mg/g at initial metal ion concentration of 200 mg/L was reported generalizing its practical use on industrial scale for water purification (Maity & Ray, 2016). In 2018, Nandkishore with his co- workers fabricated novel hydrogel by grafting guar gum with acrylic acid and cross-linking it with ethylene glycol di methacrylic acid (GG-AA-EGDMA). GG-AA-EGDMA has been found to be superadsorbent and moisture retaining material and being utilized for agricultural applications. An adsorption of about 800 mL water per gram of hydrogel has been reported. Its addition to agricultural soil resulted in enhanced porosity and retention capacity (Thombare et al., 2018).

Guar gum hydrogels are biodegradable in nature and their degradability depends upon the enzyme catalyzed breakdown and hydrolytic degradation. Degradation of guar gum and other polymers depends strongly upon the solution pH, temperature, humidity and oxygen content, etc. Due to the high flexibility, water retaining capability and biocompatible nature, guar gum based hydrogels are utilized widely for biomedical applications. Usually, soil burial and compositing methods are employed for checking the biodegradability studies. In soil burial method, the samples are buried in the soil and are subjected to ambient temperature. The biodegradability of samples under consideration is determined in terms of weight loss. However, in compositing method, the samples are buried in the compost consisting of varied microbial species. Kaith and co- workers studied about the biodegradability of different hydrogels; guar gum, guar gum- crosslinked-poly (acrylic acid) and guar gum- crosslinked- poly(acrylic acid-ipn-aniline) using soil burial and composting method. Results obtained by soil buried method shows that guar gum was completely degraded within 7 days and within 14 days by compositing method (Kaith et al., 2015). The other two hydrogels took around 50–70 days for their complete degradation and were found to depend strongly on pH and results have been presented in Fig. 3.

Guar gum based films possess exceptionally high mechanical strength, enhanced barrier properties and antimicrobial or microbe resistant properties. Films based on pea starch-guar gum biocomposite edible films as fabricated have revealed that these edible films can be used as an active agent for food packaging applications. It actually possess some antimicrobial agents which enhances its utilization (Saberi et al., 2017). In addition, guar gum/Ag-Cu nanocomposite films have also been synthesized via solvent casting method. It has been utilized as an active food packaging material due to excellent thermo-mechanical, antibacterial and O2 barrier properties (Arfat et al., 2017). Rao with his co- workers worked on the preparation of chitosan- guar gum based films and studied their properties. They synthesized the films using casting method by employing guar gum and chitosan in various ratios. The concentration of guar gum ranged from 0% to 50% (v/v) and the optical properties such as transparency, opacity, water vapour transmission rate, oxygen permeability and colour change were investigated. Variable amount of guar gum addition changed the transparency and opacity of the films. Films were evaluated for mechanical and antibacterial properties. Results conferred that films containing 15% (v/v) guar gum showed very low oxygen permeability, good tensile and puncture strength and the antimicrobial activity of films containing 15% (v/v) guar gum to chitosan were appreciable against Escherichia Coli and Staphylococcus aureus. Composite films fabricated by chitosan and guar gum may diminishes the environmental issues related with synthetic packaging as these are biodegradable in nature (Rao et al., 2010).

Nanocomposites are the multiphase solid materials in which at least one of the phases shows dimensions in the nanometre range (1 nm = 10−9m). These materials have emerged as suitable alternatives to overcome limitations of microcomposites and monolithics. They are stated to be the 21 stcentury materials in context of design distinctiveness and enhanced or unique properties (Schmidt et al., 2002). Nanocomposites display exceptional properties, due to nanometric size effect as compared to the conventional composites. Various biopolymers such as starch (Sharma et al., 2017b), cellulose (Gupta, Agarwal, et al., 2015; Gupta, Saleh, et al., 2015; Rathore et al., 2013), pectin (Kumar et al., 2018; Naushad et al., 2018; Pathania, Sharma, et al., 2016), gum ghatti (Kumar, Naushad, et al., 2017), chitosan (Kumar, Sharma, et al., 2017; Pathania, Gupta, et al., 2016) and gelatin (Thakur, Pathania, et al., 2017; Thakur, Sharma, et al., 2017) etc. has been used for the preparation of number of nanocomposites. Recent years have reported the marked increase in use of various guar gum based nanocomposite materials and have been employed for various applications (Sharma et al., 2018).

Silica is one of the most abundant mineral in the earth’s crust and is colourless in appearance. Due to its relatively high availability, it has been used for the preparation of a number of economically important materials. Examples include acrylic acid grafted guar gum nanosilica, hydrolysed guar gum nanosilica, guar gum mesoporous silica nanoparticle and cationic guar gum/silica etc. Cationically modified guar gum/SiO2 hybrid nanocomposite has been prepared and used as highly efficient anionic dye (Reactive blue and Congo red) removing agents. Nanocomposite even showed high reusability generalizing high utilization in water treatment (Pal et al., 2015). Guar gum- mesoporous silica based nanocomposites can also be used for drug delivery applications. A mesoporous silica based colonic enzyme responsive drug delivery system has been reported for the first time through proof of concept studies. Guar gum capped mesoporous silica nanomaterials (GG-MSN) have the tendency of loading a model therapeutic drug; 5FU (Kumar, Naushad, et al., 2017, Kumar, Sharma, et al., 2017). Acrylic acid grafted guar gum nanosilica used for controlled transdermal release of diclofenac sodium (Arindam Giri et al., 2013). Hydrolyzed guar gum nanosilica synthesized by sol-gel technique which achieved superior adsorption efficiency and selectivity towards both cationic dyes and metal ions in aqueous environment (Patra et al., 2017).

The complexation of guar gum with biotite mica has been examined through adsorption, flotation and electrokinetic measurements. Increase in pH enhanced the adsorption process and the isotherm studies exhibited Langmuir behaviour. Treatment of biotite mica with EDTA (complexing agent) resulted in decreased adsorption density, emphasising the influence of metal ions in the adsorption process. An increase in the surface-to-edge ratio resulted in increase in the adsorption density. The adsorption process was found to be intensely dependent upon the pH of the reacting medium. Electrokinetic measurements reported conformational rearrangements of the complex molecules with the loading, resulting in the replacement of shear plane. Dissolution experiments denoted the discharge of metal ions from biotite mica and co-precipitation tests endorse the polymer-metal ion interactions in the bulk solution (Rath & Subramanian, 1997).

Metal embedded guar gum nanocomposites have brought a blown in the functioning of the composite materials in context of its properties and application field that originates due to multifunctionality. Metals such as iron, silver, gold, potassium and phosphorus etc can be entrapped in the polymeric matrix which in turn enhances the binding, thickening and water retaining abilities of the composites.

Nickel is one of the most abundant transition metal in nature. Nickel on combination with guar gum helps in increasing its catalytic properties. Ni nanoparticles embedded in carboxymethyl guar gum (CMGG) polymer where the composite helped in the stabilization of Ni nanoparticles which otherwise get affected by aerial oxidation. The composite exhibited high superparamagnetic nature and catalytic capacity. The fabricated composite acted as a catalyst that helped in the reduction of 4-nitrophenol to 4-aminophenol in presence of sodium borohydride, acquiring complete conversion under specific conditions (Sardar et al., 2017). Iron, one of the most promising metals due to its superior magnetic properties and easy separable nature offers a wide range of applications. High adsorption ability of iron was utilized by Sharma and his- workers for synthesizing Pectin-crosslinked-guar gum/SPION nanocomposite hydrogel by co-precipitation/polymerization method. It was used as adsorbents for the removal of highly toxic m-cresol and o- chlorophenol from aqueous solution with high adsorption capacities of 176.1 and 75.6 mg/g respectively. Magnetically active nature of the nanocomposite hydrogel offers the easily separable ability and thus reducing the water toxification issues after use (Sharma et al., 2017a). Another nanocomposite based on Fe3O4-guar gum has been synthesized using ultrasonic co- precipitation method of size 48 nm and applied for the catalytic reduction of p- nitroaniline (Balachandramohan et al., 2018). An electrically conducting nanocomposite namely silver/guar gum/poly(acrylic acid) nanocomposite has been synthesized using alkaline epichlorohydrin as the crosslinking agent. This paper undertook the various factors affecting the grafting of silver onto the polymeric matrix (Abdel-Halim & Al-Deyab, 2014). Organic- inorganic combination based nanocomposite such as SnO2 nanoparticles encapsulated into gaur gum designed by sol- gel technique for the determination of hydrazine. It actually represents a striking system for the electrochemical studies (Malik et al., 2015). Dye when present in water systems limits the penetration of sunlight into the water bodies which decreases the rate of photosynthesis. Guar gum/Al2O3 designed by sol- gel method has also been reported in literature whose photocatalytic ability for the degradation of highly toxic malachite green dye from aqueous solution was determined. 90% malachite green degradation was recorded with only 30 mg of photocatalyst; GG/Al2O3 (Pathania, Katwal, Sharma, Naushad, et al., 2016).

Guar gum and its derivatives are used in many industries due to unique combination of properties. They have proved to be a valuable aid in multitude of industrial applications. Gaur gum has high capability to form viscous dispersion or gel in aqueous media hence acts as potential candidate employed for diverse applications. The glycosidic linkage of guar gum can easily be degraded by large intestine by the microbial enzyme action. Presence of large number of hydroxyl groups in the structure of guar gum make them suitable for various chemical reactions. It has been extensively employed for drug delivery applications due to its high swelling characteristics which can easily be modified by grafting and derivatization. In tablet dosage form, guar gum and its derivatives are extensively used as binder and disintegrating agent providing cohesive nature to the drug (Kumar et al., 2018; Soumya et al., 2010). It forms unique derivative molecules due to its polymeric nature and presence of functional groups that aids in conjugating the structure with different molecular weight polymers (Al-Saidan et al., 2005; Prabaharan, 2011; Tripathy & Das, 2013). Various applications of guar gum have been presented in Fig. 4.

High solubility in hot as well as cold water, solvent resistant film forming tendency, protective colloid, high viscosity, extensive pH resistance range, stability, non-toxic nature, safe and cheaper prices etc makes guar gum useful for cosmetic applications. Guar gum in tooth paste is used for imparting it a flowing nature so that paste can be extruded from portable tubes even when small amount of force is applied. Likewise, guar gum is also used in shaving creams where it acts as a stabilizing agent and helps in improving the facial skin (Patel et al., 2014). In emulsion systems like cream and lotions, guar gum is used to prevent phase separation, increase emulsion stability and avert water loss. In cold creams, it thwarts the degradation of emulsion due to freeze-thaw conditions which cause the water phase to condense out of the system.

Guar gum finds its vast usage in food industries due to its unique functional properties like high water retention capability, reduced evaporation rate, amendment in freezing rate, modification in ice crystal development and involvement in chemical transformation. The regulation of guar gum as food additives are generally documented by Food and Drug Administration (FDA). The maximum permissible limit for the use of guar gum in chapatti is 0.75% (Ghodke, 2009), in bread is 0.5% (Keskin et al., 2007), in fried products is 0.5–1% (Sakhale et al., 2011), in yoghurt is 2% (Brennan & Tudorica, 2008), in cake is 0.15% (Zambrano et al., 2004), in sausage is 0.13–0.32% (Andrès et al., 2006), in pasta is 1.5% (Raina et al., 2005) and in ice cream is 0.5% (Sutton & Wilcox, 1998). Table 2 represents the function of guar gum in various dietary products with their permissible dosage amount. For food purposes, the permissible concentration of guar gum is less than 2%. It helps in improving the viscosity, bloom, gel creation, glazing and moisture retention. In addition, also used for emulsification, stabilization, preservation, water retention and enhancement of water soluble fibre content. It enhances the yield dough in baked goods by reducing the unparalleled moisture of the dough and also reduces the fat penetration. It helps in the thickening of milk, yoghurt and liquid cheese dairy products. Furthermore, it aids in maintaining the consistency and texture of ice creams. Also, it can be used as viscosity controlling agent as well as calorie reducing agent in beverages. It obtains synergistic effect in viscosity preferred to be combined with other gums like gum tragacanth, karaya gum, xanthan gum and other cellulosic gums.

Recent years have marked the use of guar gum and its derivatives for the formulations in drug delivery systems. Tendency of guar gum to act as binder, disintegrating agent, thickener, stabilizers, emulsifier and suspending agent make it applicable for use in drug delivery systems. However, properties of guar gum can be altered to get diversified solubility, swelling and film forming ability. Guar gum, due of its flexibility to attain an appropriate drug release profile and cost-effectiveness has been widely used for targeted drug delivery in diverse forms such as tablets matrix, hydrogels and nanoparticles etc. It has excellent bio adhesive properties. Strong interactions between guar gum and mucus lining of the tissue, increases the contact time and localization at the site of contact. The cross linked semi synthesized guar gum derivatives like glutaraldehyde crosslinked guar gum, hydroxyethyl guar gum, hydroxyl methyl guar gum and 4-vinyl pyridine conjugated guar gum, etc have been used in the novel drug delivery system. It can also be used as the most prominent candidate for antihypertensive drug delivery systems due to its stability under shear stress conditions.

Recent studies have revealed the use of guar gum and its derivatives as a matrix for the colon specific controlled release of dexamethasone and other anti-inflammatory agents (Wong et al., 1997) such as indomethacin (Prasad et al., 1998), albendazole (Krishnaiah, Raju, et al., 2001; Krishnaiah, Seetha Devi, et al., 2001), metronidazole (Krishnaiah et al., 2002) and mebendazole (Krishnaiah, Raju, et al., 2001; Krishnaiah, Seetha Devi, et al., 2001) etc. Microparticles of guar gum- succinic anhydride crosslinked with sodium trimetaphosphate were tested as a carrier for drug delivery (Seeli & Prabaharan, 2016). Due to its pH dependency and no cytotoxicity, the prepared material was found to be excellent carrier for colon-specific drug delivery. The drug releasing rate of the guar gum depends intensely on the ionic strength of solution, pH of the solution and extent of grafting. For example, poly(acrylamide) grafted guar gum, tested for the in-vitro release of 5-amino salicylic acid shown that increase in extent of grafting decreases the rate of drug release (Sen et al., 2010). Similarly, release of ketoprofen by amphiphilic guar gum grafted with poly(ε-caprolactone) (Tiwari & Prabaharan, 2010) was found to be maximum in alkaline pH. Table 3 represents guar gum and its various derivatives being employed for numerous biomedical applications.

Guar gum and its derivatives have been extensively employed in many industries such as textile, oil field and explosive etc underlying various properties such as ability to act as superior thickener, stabilizer, gelling agent, binding agent, emulsifier, flocculent and fracturing agent etc. In textile industries, guar gum and its derivatives provide excellent film forming and thickening properties particularly when utilized for finishing and printing. It helps in reducing breakage and dusting while sizing. In addition, also increases the production efficiency. It even thickens the dye or imprinting solutions which let the printed patterns to be sharper. However, in explosive industries, guar gum is used because of its improved swelling, water blocking and gelling properties.

Guar gum acts as water soluble and bulk forming laxative fibre. It is effective in promoting regular bowel movements, relieving constipation, Crohn’s disease, diverticulosis, irritable bowel syndrome and colitis, etc. Guar gum and its derivatives can be employed for physiological disorders. Literature has revealed that nine months contact with granulated guar gum can treat hypercholesterolemia and the results were quite long term (Bradley et al., 1989). In addition to hypercholesterolemia, cholera and diarrrhoea in adults can also be treated by the use of guar gum and its derivatives (S. Tripathy & Das, 2013). Gamal with his co- workers reported the synthesis of C-glycosylated guar gum and its sulphated derivatives and found to have chemopreventive and anti-inflammatory properties which helps in averting cancer by obstructing carcinogen activating enzymes and endorsing the carcinogen detoxification enzyme glutathione-S-transferase (Kono et al., 2015).

One of the most threatening problems faced by the world today is pure water scarcity. Due to rapid development in industrialisation, number of toxic or noxious pollutants such as dyes (malachite green, safranin, fast green and rhodamine B), heavy metal ions (Pb2+, Cd2+ and Zn2+ etc) and organic compounds such as (pesticides, fungicides and herbicides, etc) are being discharged into the water bodies without any pre- treatment (Sharma et al., 2017b; Sharma et al., 2018). Their removal from the water bodies is need of the hour. Guar gum having ability of coupling with high polymeric groups and other materials not only enhances its properties but also results in increase in their application diversity. Guar gum based composites such as guar gum grafted onto multiwall carbon nanotube (MWCNT) and iron oxide nanoparticles (GG–MWCNT– Fe3O4) are used as adsorbents for the exclusion of industrial dyes such as neutral red and methylene blue dye from the wastewater or other aqueous systems. Due to magnetic nature, composite presented easy separation from the aqueous solution in the presence of external magnetic field (Yan et al., 2012). Sharma with his co- workers in 2018 tried to crosslink guar gum with soya lecithin and resulted in formation of nanohydrogel sheets that were employed for the removal of fungicide; thiophanate methyl from the aqueous solution of concentration 25 ppm. Interactions favouring the adsorption of thiophanate methyl onto nanohydrogel sheets were π-π interactions and dipole- dipole H- bonding. Fig. 5 shows the adsorption mechanism of thiophanate methyl onto nanohydrogel sheets (Sharma et al., 2018).

An adsorbent based on guar gum embedded with silica nanoparticles (h-GG/SiO2) has been utilized efficiently for the water detoxification. It has been used for the adsorptive removal of toxic cationic dyes (malachite green and safranin) and metal ions (Pb2+ and Cd2+) from the aqueous solution. High adsorption capacity of 781.25 mg/g, 281.69 mg/g, 645.16 mg/g and 709.21 mg/g was recorded for the malachite green, safranin, Pb2+ and Cd2+, respectively (Patra et al., 2017). In addition, biopolymeric guar gum was used for the removal of lead ions from the aqueous solution. The separation process was based on the coagulation/flocculation treatment which resulted into 83% Pb2+ ions removal at flocculent dose of 1.25 mg/L. Removal was found to be strongly dependent on the pH of the medium (Mukherjee et al., 2018). Borax- crosslinked guar gum hydrogel provides another material with superior abilities for water detoxification. The hydrogel was utilized for the removal of aniline blue from aqueous solution and the separation efficiency was found to be dependent upon various factors such as pH, presence of counter ions in the solution, temperature and time of contact etc (Thombare et al., 2017). Table 4 represents guar gum and its various derivatives being used for water purification application.

Section snippets

Conclusions

In this review paper, we found that guar gum and its composites are equipped with multiple physical and chemical properties. Naturally occurring polymers are of crucial importance among which guar gum occupies distinct position for its easy availability, non-toxic and biodegradable nature. Guar gum achieves its full viscosity even in cold water disparate from other gums that require persistent hot water treatment for attaining the same viscosity. It can be intermingled with other gums like

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