Fenugreek (Trigonella foenum graecum) gum: A functional ingredient with promising properties and applications in food and pharmaceuticals—A review

Fenugreek (Trigonella foenum graecum) is an annual plant belonging to the family Leguminosae or Fabaceae. The seeds of fenugreek contain 26.8% soluble fiber chemically identified as galactomannans with properties similar to soluble fiber of guar seeds and psyllium husk and so on. Galactomannans are biopolymers consisting of linear core poly (1,4)‐β‐D‐mannan backbone having varying degrees of D‐galactosyl substituents attached by 1,6‐glycosidic linkages. Different galactomannans derived from various legumes usually differ in molecular weight, ratio of mannose to galactose, and the mode and place of linkages of galactose moieties to the mannan backbone. Fenugreek gum has a galactose to mannose ratio of 1:1, showing the highest amount of galactose resulting in its highest water solubility compared with guar and locust bean gum. It suggested that the galactose and mannose moieties are linked uniformly in fenugreek gum resulting in maximum hydration and solubility. This M/G ratio affects the physicochemical properties of galactomannans and is inversely related to the solubility of gum. Galactomannans sterically stabilize the emulsions against flocculation and coalescence by getting adsorbed onto oil droplets. In addition to this, galactomannans are all found to exhibit some surface, interfacial, and emulsification activities. Because of these properties, it is preferred over other natural hydrocolloids as an excellent ingredient for various food applications. As a hydrocolloid, fenugreek gum provides texture, appeal, gelling, thickening, emulsifying, stabilizing, and encapsulating properties. In the present review, we summarized the extraction, purification, chemical, functional properties, molecular structure, thermal and rheological behavior of gum isolated from fenugreek seeds, and then vital application of this traditional source of hydrocolloids in food, pharmaceutical, and other industries.

Fenugreek gum is often composed of galactomannans in which the common ratio of galactose to mannose is 1:1.1. Its molecular structure is composed of a (1 ! 4)-β-D-mannan backbone to which single α-D-galactopyranosyl groups are connected at the C-6 position of the D-mannopyranosyl residues (Brummer et al., 2003). The polymer has high molecular weight, is rich in hydroxyl groups, and easily forms hydrogen bonds with water to form a viscous solution. The galactomannans are nontoxic (Noleto & Petkowicz, 2016), highly-soluble, film-forming (Kurt & Kahyaoglu, 2014), and controlled-release (Burke et al., 2005) polymers and can also be used as an alternative material for synthetic polymers (Salarbashi et al., 2019). Various researches have focused on the characterizations of fenugreek gum and evaluation of its potential applications in foods, food products, pharma, and textile and different industrial uses. This review article narrates the physicochemical and functional properties along with recent chemical modifications of fenugreek gum. It also gives insights into understanding fenugreek as a potential gum source for its vital applications.

| SOURCE AND STRUCTURE
Polysaccharide gum is one of the major industrial raw materials and the topic of comprehensive research because of its sustainability, T A B L E 1 Sources and monosaccharide composition of some major gums

| EXTRACTION AND PURIFICATION
In general, salt solution and water are used to extract gum from fenugreek seeds. Rashid et al. (2018Rashid et al. ( , 2020 solubilized fenugreek gum by mixing defatted fenugreek seed powder in salt solution with the pH adjusted to 3 (using acetic acid). The mixture was then placed in water bath at 50 C for 24 h with occasional stirring at 250-300 rpm. The solubilized gum was then sieved and centrifuged to separate residual seed materials and impurities. To precipitate gum from the solution, a combination of ethanol and isopropanol (9:1 v/v) was added at a volume ratio of 3:1 (mixture/gum solution) under vigorous stirring. The precipitated fenugreek gum was collected by centrifugation, redissolved, and reprecipitated to extract notably whiter and salt-free and acid-free fenugreek gum. Further purification of fenugreek gum can be attained by treating the gum solution with a pronase enzyme to reduce its protein content up to 0.57% (Brummer et al., 2003). In one another study, phenol solvent treatment decreased the protein content of fenugreek gum to 0.16% (Youssef et al., 2009). Rashid et al. (2018 redissolved the separated fenugreek gum in double distilled water (250 ml) and similarly purified it by using the equal combination of ethanol and isopropanol. The purification of fenugreek gum decreased the galactose and mannose (G/M) ratio from 1.00:1.20 to 1.00:1.23; this value is slightly lower than the value (1.00:1.05) obtained by Brummer et al. (2003). This difference in G/M ratio may be due to differences in plant source as well as the extraction process.
A fenugreek gum yield of 10%-15% is generally reported by several researchers Iurian et al., 2017 (Salarbashi et al., 2019). The extraction and purification process of fenugreek gum is presented in Figure.1.

| CHEMICAL COMPOSITION
The chemical composition of fenugreek gum and different gums is shown in Table 2. The functionality of any gums such as emulsifying, film forming, and water solubility depends especially on their chemical composition (Abazovi c et al., 2006). Fenugreek gum has shown a moisture content of 7.5%-10.6% (Brummer et al., 2003;Jiang et al., 2007;Rashid et al., 2018), which was higher than that of flaxseed gum (4.1%) and some other gums demonstrated in Table 2. It has a relation with monosaccharide composition and structure of gums. The variation in the availability of hydrophilic sites that hold water molecules in polysaccharide chain may be the cause of their differential moisture content . Significant variations have been reported in the fat content of different gums, which may be due to the difference in extraction and purification process (Hamdani et al., 2019). In general, fenugreek gum has been found with low fat content (0.5%-1.6%; Table 2). The protein content of fenugreek gum was higher than that of other gums in the range of 0.78%-1.5% (Brummer et al., 2003;Jiang et al., 2007;Rashid et al., 2018).
However, in addition, research is needed to inspect the fatty acid, protein, amino acid, and mineral profile of fenugreek gum in order to determine its general nutritional scores as food additives.

| Monosaccharide composition
Regarding the composition of sugar monomers (Table 3)  In comparative studies by some other researchers also, fenugreek gum showed lower M/G values (1.1-1.2) compared with guar gum (1.65 to 1.7), tara gum (3.0), locust bean gum (3.7), and Gleditsia sinensis gum (3.55) (Liu et al., 2020;Wu et al., 2009). The G/M ratio is generally considered a determinant factor in the prediction of galactomannan functional properties. For example, edible films made from galactomannans with high G/M ratios are highly permeable to oxygen and poorly soluble in water (Mikkonen et al., 2007).

| Bulk density
Bulk density depends on many factors, including shape, size distribution, interparticle forces, particle size, and number of contact points.
The bulk density (Table 4) of various gums ranged from 0.43 to 1.24 g/ml; the values for fenugreek gum ranged between 0.615 and 0.735 g/ml Rashid et al., 2018); higher than kenaf and locust seed gum but lower than guar gum, tragacanth gum, and so on. In general, materials with lower bulk density have higher porosity and vice versa. greek galactomannans make it ideal as a stabilizer or anti-synergism ingredient in food products.

| Oil holding capacity (OHC)
The protein content, surface area, porosity, and capillary motion are different elements that affected the OHC of polysaccharides (Chau & Huang, 2003). As shown in Table 4

| Foam capacity (FC) and foam stability (FS)
Whipping gums cause the formation of foams, which can be attributed to the development of a stable network capable of withstanding smaller solute particles. The FC of fenugreek gum aqueous dispersions as a function of concentration showed that fenugreek gum had a significantly higher FC (15%) than guar gum (8%) (Rashid et al., 2018).
Also, fenugreek gum maintained stable foam volume compared with guar gum foam, suggesting its application as a foam stabilizer in frothy beverages such as cappuccino and beer (Rashid et al., 2018).
FC is attributed to the ability of a molecule to decrease the surface tension of the water and air interface; it is directly linked to the equilibrium surface tension (Wilde, 2000). These foaming properties of fenugreek gum may be contributed by the glycoprotein complex because of protein accompanying the polysaccharide in the extract.
This enables the galactomannans to minimize the surface tension and show more FC (Naji et al., 2013). In a study on fenugreek gum

| Swelling index (SI)
Fenugreek gum demonstrated significantly higher values for SI in contrast to guar gum and different gums (Table 4). SI showed a concentration-dependent behavior and increased with increasing gum concentration . Kaur et al. (2018) suggested that higher SI is associated with increased viscosity because of increased flow resistance. Therefore, galactomannans impart high viscosities to the solution when added as a food ingredient and exhibit great potential for utilization in beverages where increased viscosities are often associated with higher pulp. Further, higher temperature processing of these products also tends to increase viscosities because of increased hydrogen bonding between gum hydroxyl groups and water molecules.

| Modification of fenugreek gum
Fenugreek gum hydrates slower than other plant-based gums because its molecule is not electrostatically charged (Salarbashi et al., 2019).
Therefore, scientific researches have focused on modification techniques of fenugreek gum (Table 5) such as extrusion, whereby extra hydrophilic groups may additionally be uncovered to water response (Chang et al., 2011;Roberts et al., 2012). They found that the hydration capability and water solubility of fenugreek gum were increased because of the extrusion process, which also affected their film forming properties (Chang et al., 2011;Roberts et al., 2012). According to Chang et al. (2011) and Pasqualone et al. (2020), extrusion can remove fenugreek gum's unpleasant flavor and color, allowing it to be used for human consumption (Senarathna et al., 2022). Chang et al. (2011) compared chemically modified fenugreek gum and extrusion-modified fenugreek gum protein content. They found that the quantity of protein in chemically modified fenugreek gum (1.85%) does not differ notably from extrusion-modified gum (1.86%-1.94%). In addition, they also found that the process of extrusion can change the distribution of fenugreek gum molecular structure and mass. The authors concluded that extruded fenugreek gum had a different molecular weight profile than non-extruded counterpart, which may be related to the breakdown of the macromolecular structure of fenugreek gum during the extrusion process. It was also found that extrusion increased gum's water solubility and hydration potential but do not affect the emulsifying or water-holding properties. Since fenugreek gum can act as an emulsifier, it will be beneficial in developing composite edible films by improving the stability of dispersed biopolymers to form a homogeneous film forming solution (Senarathna et al., 2022).
Enzymatic treatments can modify the structure of galactomannans to improve their functionality. Endomannanase (EC 3.2.1.78) cuts inner linkages between mannose moieties in the backbone, and α-galactosidase (EC 3.2.1.22) cleaves galactose subunits to reduce polymerization and substitution. As a result, the gelation properties of galactomannan can be increased (Mikkonen et al., 2007). By using α-galactosidase, the galactose substitution of fenugreek gum can be reduced to an optimal level, which can improve film making properties (Senarathna et al., 2022). As a result, lowering the G/M ratio can help to create a more robust film structure with better mechanical and barrier properties. Therefore, scientific research is needed to identify the optimal G/M ratio and degree of polymerization for fenugreek galactomannans to improve film forming properties (Senarathna et al., 2022).
In one another modification, fenugreek gum was hydrophobically modified and stearic acid was conjugated with fenugreek gum by a simple esterification reaction. The results suggested that the resultant conjugate can be successfully employed for a liver-targeted drug delivery (Zhou et al., 2019). Fenugreek gum can be chemically modified by cyanoethylation using acrylonitrile or oxidation (using sodium chlorite with urea were also explored as thickening agents in textile printing (Ragheb et al., 2015).

| Rheological properties
The viscosity of hydrocolloids indicates their ability to act as an emulsifier, stabilizer, or suspending agent (Salarbashi & Tafaghodi, 2018).
Several variables, including concentration, temperature, pH, time, shear rate, and the presence of sugar and salt as solvents, were reported to alter the rheological properties of gum solutions . A comparative summary of rheological behavior of different galactomannans is presented in Table 6.

Effect of concentration
According to a study (Wei et al., 2015), which looked at the steady flow behavior of fenugreek gum solutions as a characteristic of polymer concentrations (0.05-2.0 percentage [w/v]), it was found that the viscosity of the solution exhibited a shear thinning behavior as the shear rate increased. For many galactomannans, such as fenugreek and different galactomannans like guar and Arabic, this behavior was expected (Albuquerque et al., 2014;Hussain, 2015). Galactomannans' shear thinning behavior was connected to the disentanglement of polymer chain in the flow direction (Benchabane & Bekkour, 2008).
Furthermore, this behavior has been linked to the alignment of polymer chains in the route of flow, which resulted in much less interactions between polymer chains (Adeli & Samavati, 2015).  also reported shear thinning behavior for solutions of gums isolated from different fenugreek cultivars.
According to Iurian et al. (2017), the viscosity of fenugreek gum solution increased manifolds (32 to 12,200 mPa.s.) when the gum concentrations increased from 0.25% to 2%. The authors suggested that the rheological statistics of the fenugreek gum solution can be effectively described by the power law model. It was stated that rise in fenugreek gum concentration was accompanied by a rise in k value, which was consistent with the findings of several other studies.

Effect of concentration
Several researchers looked into the dynamic viscoelastic properties of fenugreek gum solutions as a function of gum concentrations (0.05%-2.00%) (Wei et al., 2015;Youssef et al., 2009 solution, which had a concentration range of 0.05%, displayed a highly viscous behavior at low frequencies, but as the frequency was raised, the behavior of the fenugreek gum changed to that of a gel.

Effect of temperature
According to a literature review, galactomannans are stable at low temperatures. Wei et al. (2015) evaluated the impact of temperature (0-80 C) on the viscoelasticity of fenugreek gum and located that at each examined concentration and temperature, the storage modulus (G 0 ) was higher than the loss modulus (G 00 ), indicating that the fenu- greek gum solution maintained their gel-like state. The temperature sensitivity of fenugreek gum solution was once concentration dependent. But at a concentration of 1.5%, the magnitude of the storage modulus lowered as the temperature of gum solution increased. This trend could be due to limited intermolecular interactions, which reduces the free energy required (Fathi et al., 2016). Initially, as the temperature of fenugreek gum solution with a concentration of 1.5% increased from 0 to 30 C, the storage modulus decreased; however, as the temperature was increased further, the storage modulus began to increase. This impact is attributed to the formation of a threedimensional network structure at high temperatures.

| Food applications
In many food industries, fenugreek gum is used in different types of food products as a novel additive for their stabilization and as a fiber source (Morris, 2010). It is consumed or favored by producers as well as consumers because of the fact of its inexpensive and natural additive values. It is used in a variety of food products as an additive (stabilizer, emulsifier, and hydrocolloid) as it can modify the behavior of water present as a common component in different foods. Some of the most generally used food applications of fenugreek gum are shown in Table 7.

| Bakery products
Fenugreek gum addition in biscuits or cake dough can improve the machinability of dough, which helps in easy emptying of dough molds and clean slicing without crumbling after baking.

| Dairy products, salad dressings, and sauces
Fenugreek gum is typically used in frozen food products such as ice cream for stabilization because of its high water binding capacity.
Fenugreek gum is also desirable in high-temperature short-time (HTST) processes because of the fact that such processes require gums that can hydrate easily and fast in a short processing time. Fruit juices and beverages 0.1-0.2 As consistency improver, better elasticity and viscosity Aruna et al., 2018;Zhao et al., 2021 Edible film coating -Film forming capability and performance Senarathna et al., 2022;Mohite & Chandel, 2020 Because of this, locust bean gum is not suitable for HTST despite having all the other ideal properties but hydrates slowly (McKiernan, 1957).
Weeping and syneresis are serious problems in cheese and cheese products. By the addition of fenugreek gum like other hydrocolloids, weeping and syneresis can be reduced by water phase management, and thus, the body and texture of cheese and cheese products can be improved (Klis, 1966). Fenugreek gum is allowed up to 3% of the total weight in cheese products; it increases curd solids and softens separated whey. Low-fat cheese can be made with fenu- greek gum at 0.0025%-0.01% w/v without changing texture, taste, or rheology compared with full-fat cheese.

| Processed meat products
Fenugreek gum has a high water retention capacity in both hot and cold water (Chang et al., 2011). Consequently, it can be used as a lubricant, stabilizer, and binder in the preparation of hotdogs, stuffed meat products, and sausages. It is reported that hydrocolloids perform several desirable functional roles such as controlling syneresis and preventing fat migration during storage in the processing of meat and meat products (Ercelebi & Ibanoglu, 2010).

| Beverages
Fenugreek gum has been successfully used in beverages because of its several inherent properties for viscosity control and thickening.
Another important property of fenugreek gum is its resistance to breakdown under low pH conditions present in beverages. Moreover, it is more soluble in cold water, which makes it easy to use in to improve the shelf life of beverages. When added to mosambi fruit juice, fenugreek gum as a clarifying agent altered its different physicochemical properties like TSS, pH, acidity, and viscosity (Aruna et al., 2018). The effects of fenugreek gum on rheological properties of quinoa juice under different storage conditions (25, 4, and À18 C) were explored (Zhao et al., 2021). The juice-gum mixture showed a pseudoplastic behavior dominated by elasticity (tan δ > 1). Also, quinoa juice showed better viscosity at 0.8% fenugreek gum concentration. Fenugreek gum has also been successfully employed in producing spray-dried powders containing encapsulated anthocyanins of black raspberry juice, and a high agreement between experimental and predicted values was reported (Yousefi et al., 2015).

| Pharmaceutical applications
Fenugreek gum, being natural, nontoxic, low cost, easy to use, and a soluble galactomannan with suitable functional properties, can be employed in various pharma applications such as ophthalmic and colon drug delivery. Fenugreek gum when employed to prepare a nanoparticulate for ophthalmic drug delivery showed blood compatibility up to 2000 g/ml (Pathak et al., 2014). Fenugreek gum can also be employed for protection and successful release of drugs/bioactive compounds in the gut and colon regions, which have different pH (7.4 and 6.8, respectively) and generally hamper the capability of pHdependent drug delivery systems (Park et al., 2010). In rats, interpolymer complex prepared using chitosan, carboxymethyl fenugreek gum and tamoxifen showed 91% release of the drug (tamoxifen) in the belly and small intestine (Randhawa et al., 2012). Fenugreek gum found its suitability for colon-specific drug delivery system because of its easy availability, lower cost, cytocompatibility, and mucoadhesive nature. However, study into fenugreek gum-based excipients for colon drug delivery is nevertheless in its early stages, so pressurecontrolled colon-specific drugs and osmotic-controlled drug delivery can be developed using fenugreek gum. These colon-specific drug delivery systems can be tested by simulating small intestine, jejunum, ileum, and gastric fluid pH conditions (Mishra et al., 2021 has better buoyancy, a longer duration of drug release, and swelling potential (Bera et al., 2016) (Table 8).
The properties such as adhesiveness and biocompatibility of fenugreek gum have found their suitability in developing dynamic drug delivery systems for the vaginal tract to deliver drug to the site of infection or injury for an extended period of time (Paveli c et al., 2001). Polymeric films having drug nystatin and made of aminated and carboxymethyl fenugreek gum with glycerol successfully delivered the drug for a longer time (8 and 5 h, respectively) and cured vaginal candidiasis in rats (Bassi & Kaur, 2015a, 2015b. As fenugreek gum is mucoadhesive, it can be used to make effective nanoparticle/emulsions and hydrogels to treat bacterial vaginosis, vulvovaginal candidiasis, urinary tract infections, aerobic vaginitis, and trichomoniasis. Fenugreek gum can also be used as a binder in tablet formulation and give the powder mass cohesiveness and convert it into granules, which are then easily compressed into tablets. Additionally, fenugreek gum has high water absorption and swelling capacity and crumbles easily, which help in disintegration of tablet (Jani et al., 2005). Also, hydrophilic polymer such as fenugreek gum is hydrated and forms gel, which helps in the delayed drug release because of their diffusioncontrolled release . This can help in sustainable release of drug and is utilized in long-term drug transport systems (Bravo et al., 2004).

| Conclusion
Fenugreek gum is an important hydrocolloid extracted from the seeds of fenugreek. It is a useful polymer to investigate attributed to its versatile properties and applications in different food and non-food industries. It has a balanced galactose-to-mannose ratio, compared with most commercial gums available such as locust bean gum and guar gum. It also has higher water and oil binding properties, which makes it an ideal thickener, stabilizer, and texture modifier. It also shows good foaming and emulsion capacities.
Because of these characteristics, it has found numerous applications in food industries, pharmacy, packaging, cosmetics, paper, oil, textile, paint, and explosive industries. Also, fenugreek gum is low cost, bio-compatible, nontoxic, and easily produced, which can also help in its enhanced utilization. As a hydrocolloid, fenugreek gum provides gelling, appeal, thickening, stabilizing, texture, emulsifying, and encapsulating properties and, therefore, can be used in bakery products, dairy, sauces, and meat industry.
Being soluble dietary fiber, it can also be used as a practical ingredient for high-fiber nutraceuticals, which now not only help in lowering blood cholesterol and coronary heart disease risk but also improve bowel movement and management in human beings.
Fenugreek has also been verified as a vital ingredient in drug delivery applications.