Fenugreek seed gum: Biological properties, chemical modifications, and structural analysis– A review

International Journal of Biological Macromolecules 138 (2019) 386–393

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International Journal of Biological Macromolecules journal homepage: http://www.elsevier.com/locate/ijbiomac

Review

Fenugreek seed gum: Biological properties, chemical modifications, and structural analysis– A review Davoud Salarbashi a,b,⁎, Javad Bazeli c, Elham Fahmideh-Rad d a

Nanomedicine Research Center, School of Medicine, Gonabad University of Medical Sciences, Gonabad, Iran Department of nutrition, School of Medicine, Gonabad University of Medical Sciences, Gonabad, Iran Department of Emergency Medicine, School of Nursing and Midwifery, Gonabad University of Medical Science, Gonabad, Iran d Applied Sciences Department, Applied Chemistry Section, Higher College of Technology (HCT), Muscat, Oman b c

a r t i c l e

i n f o

Article history: Received 31 October 2018 Received in revised form 30 June 2019 Accepted 1 July 2019 Available online 2 July 2019 Keywords: Fenugreek seed gum Physico-chemical properties Functional properties

a b s t r a c t Fenugreek is a leguminous plant belongs to the family Fabaceae, which is extensively cultivated as a semiarid crop in Northern Africa, the Mediterranean, India, and Canada. In the present review paper, first we summarized the extraction, purification, chemical composition, molecular structure, and rheological behavior of the mucilages isolated from Fenugreek seeds (FSG), and then their functional properties presented to elucidate the potential application of this traditional source of hydrocolloids in food, pharmaceutical, and other industries. To date, there is no technique that can successfully remove the attached protein from FSG. From a structural point of view, galactose and mannose are the most abundant polysaccharide in FSG composition, suggesting a galactomannan-like structure. FSG is the most soluble of the seed gums. FSG solutions at various temperatures and concentrations showed a time-dependent shear thinning behavior. Furthermore, these hydrocolloids can be employed for the fabrication of eco-friendly packaging systems. Antioxidant capacity and anti-fungi activity of FSG has been proved in different studies. In conclusion, industrial applications of FSG are possible due to its strong thickening properties. Additionally, FSG has an excellent emulsification capacity, which enables its application in the food, cosmetic and/or pharmaceutical industries. © 2019 Elsevier B.V. All rights reserved.

Contents 1. 2. 3. 4. 5. 6.

Introduction . . . . . . . . . . . . . . . . . Extraction and purification of FSG. . . . . . . . Chemical properties and modification of the FSG . Physical properties . . . . . . . . . . . . . . Colloidal dispersion properties . . . . . . . . . Functional properties . . . . . . . . . . . . . 6.1. Emulsifying properties . . . . . . . . . 6.2. Rheological behavior . . . . . . . . . . 6.2.1. Steady-state rheological behavior 6.2.2. Dynamic rheological behavior . . 6.3. Hydration properties . . . . . . . . . . 6.4. Oil holding capacity (OHC) . . . . . . . 6.5. Construction of edible films . . . . . . . 7. Biological activity . . . . . . . . . . . . . . . 8. Conclusion . . . . . . . . . . . . . . . . . . 9. Future trends and perspective . . . . . . . . . References. . . . . . . . . . . . . . . . . . . . .

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⁎ Corresponding author at: Social Development & Health Promotion Research Center, Gonabad University of Medical Sciences, Gonabad, Iran. E-mail address: [email protected] (D. Salarbashi).

https://doi.org/10.1016/j.ijbiomac.2019.07.006 0141-8130/© 2019 Elsevier B.V. All rights reserved.

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D. Salarbashi et al. / International Journal of Biological Macromolecules 138 (2019) 386–393

1. Introduction Fenugreek is a leguminous plant belongs to the family Fabaceae, which is extensively cultivated as a semiarid crop in northern Africa, the Mediterranean, India, and Canada [1]. It has been reported that fenugreek could be employed in the medicinal, pharmaceutical and nutraceutical fields [2]. Fenugreek seeds are used in traditional medicines for promoting digestion and reducing blood sugar levels in diabetics [3–5] and controlling plasma cholesterol level [6]. It also has been reported that the seeds and the leaves of fenugreek are consumed as spice and green vegetable, respectively [7]. These effects have been attributed to the compounds abundant in the seeds, leaves, and mucilage of fenugreek [8]. When fenugreek seeds were wetted by water, they produce a transparent gum. It has been reported that the mucilage extracted from the seeds of fenugreek is about 25% g/g seeds; which can be used as a thickening, stabilizing and emulsifying agents in food products [3,9]. Various studies have focused on the characterization of fenugreek seed gum (FSG) and evaluation of its potential application in food, pharmaceutical, textile, cosmetic and other industries. This review presents an overview of FSG extraction methods, its physico-chemical properties and its potential application in various industries. 2. Extraction and purification of FSG The average extraction yield of FSG is 15.04% (w/w) [10]. Comparatively, this value is slightly higher than those reported for Descurainia sophia seed gum (10.45%) [11], Durio zibethinus seed gum (1.2%) [12], and lower than that of Lallemantia ibrica seed gum (23.82%) and Mesquite seed gum (24.9%) [13]. The extraction yield for FSG obtained here is different from those reported by other researchers [14,15]. The observed difference could be associated with the variability between plants cultivated in different geographical areas [16]. Many researchers have been focused on removing the attached protein from FSG [17,18]. There is no technique that can successfully remove the attached protein from FSG and justified as due to the high partition coefficient of the mixture of biphasic water-phenol, the attached protein can be successfully removed under the controlled conditions [19]. Garti, Madar, Aserin and Sternheim [20] used a physical method to purify FSG. They prepared a fenugreek crude solution (1 g protein/kg FSG) and then injected it into a Florisil column (150 mm length 325 mm diameter) of 200 meshes with double distilled water. It was observed that the purified gum had about 10 g protein/kg FSG. Brummer, Cui and Wang [21] indicated that the enzymatic treatment of FSG (treating the gum solution with Pronase) decreased the attached protein of FSG to 0.57%. In another study, the protein attached to FSG was removed by phenol solvent treatment [7]. After treatment, the protein content of FSG decreased to 0.16%, which is lower than the data reported by Garti, Madar, Aserin and Sternheim [20] and Brummer, Cui and Wang [21] (Table 1). 3. Chemical properties and modification of the FSG Chemical characterization of hydrocolloids is one of the primary ways to predict their functionality [78]. For example, the ability of hydrocolloids to reduce the surface tension, film-forming as well as their water solubility is mainly dependent on their chemical composition. Various techniques are commonly used to evaluate the chemical properties of hydrocolloids including high-pressure anion exchange, gel permeation, gas chromatography, FTIR and NMR. So far, various studies have been focused on the evaluation of the gum extracted from fenugreek seeds. The chemical composition of FSG is mainly dependent on the extraction technique used and its variety/cultivar [22]. Hence, the chemical composition data reported in literature should not be considered as absolute results. The commercial

387

FSG products are composed of polysaccharide and protein with respective values of 80%and 5%, respectively. When pronase, as a nonspecific protease was used in FSG production process, a gum with higher purity (0.6% protein) obtained [21]. The proximate analysis of crude FSG, purified FSG and protein free FSG is given in Table 2. It is shown that the protein content of the gum considerably decreased when the gum was treated by pronase. Proteins impart emulsifying capability to polysaccharides. Therefore, it is expected that crude FSG is better emulsifier than purified and free protein FSG. There are few studies on chemical modification of FSG [23,24]. According to the literature, some chemical modifications like extrusion can changed the conformational properties of gums, whereby there may be more hydrophilic groups exposed for reaction with water. Chang, Cui, Roberts, Ng and Wang [24] compared the protein content of FSG and extrusion-modified FSG (EMFSG). It was observed that the amount of protein in FSG (1.85%) was not substantially different from that of EMFSG (1.86–1.94%). Furthermore, they found that extrusion process may change the distribution of molecular mass of FSG. It also was reported that extrusion process enhanced water solubility and hydration capacity of the gum. But, extrusion had no considerable effect on emulsifying properties and water holding capacity of the gum. Surprisingly, extrusion process led to removing the unpleasant flavor associated with the original BSG. Roberts, Cui, Chang, Ng and Graham [23] used extruded and nonextruded FSG was a substitute for wheat flour and then evaluate the rheological effects and bread-making properties. The authors indicated that extrusion resulted in an increase in water solubility and water absorption of the gum. Since the monosaccharide composition of the hydrocolloids has a profound effect on their rheological and functional properties, determination of monosaccharide composition of gums is the first step for exploring their potential application in food, pharmaceutical and other systems [16,25,26]. The monosaccharide composition of FSG reported in previous studies is summarized in Table 2. It can be seen that mannose and galactose are the most abundant monosaccharides of FSG, demonstrating a galactomannan structure for this gum. It is observable that there is the difference between the monosaccharide composition of FSG reported by different studies, which may be attributed to the various factors like as the age of the plant, the purification method, and growing conditions [25,27]. The ratio of galactose (G)/mannose (M) is commonly considered as a determinant factor in predicting the functional characteristics of the galactomannan [28]. For example, the edible films fabricated by galactomannan with more G/M ratio have more oxygen permeability and lower water solubility [29]. Comparatively, the G/M ratio of FSG is close to guar gum (1.62) [30] and less than the data documented for locust bean gum (3.5–4) [31]. Accordingly, due to the similarity of G/M ratio of FSG and guar gum, FSG can be used as an appropriate alternative for guar gum. The molecular weight properties of hydrocolloids have a considerable effect on their functional properties like as gelling and stabilizing properties. For example, the gums with high molecular weight like as xanthan have good thickening properties [32]. Furthermore, it has been reported that high molecular weight polysaccharides can improve the stability of protein foams [33]. Wei, Lin, Xie, Xu, Yao and Zhang [34] determined some molecular parameters of FSG include average molecular weight, molecular weight (Mw), average number of molecular weight (Mn) and polydispersity index (PDI = Mw/Mn), as shown in Table 3. Thus, it is expectable that FSG also can be introduced as a viable stabilizer in protein foam systems. According to Chang, Cui, Roberts, Ng and Wang [24], extruded-FSG had different molecular weight profile than non-extruded one. The authors reported that this effect may be related to the breakdown of the macromolecular structure of FSG during the extrusion process. Similar observations have been reported for polysaccharide extracted from the cell wall of onion waste [35], and anionic starch [36].

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Table 1 Effect of extraction and purification technique on some physic-chemical properties of FSG. Brummer, Cui and Wang [21]

Youssef, Wang, Cui and Barbut [7]

Garti, Madar, Aserin and Sternheim [20]

Protein contaminates: (before and after enzymatic treatment were 2.36% and 0.57%, respectively); Purified gum had less surface activity than crude one; Enzymatic treatment did not affect the molecular weight of the gum; Enzymatic removal of protein decreased the ability of FSG to reduce interfacial tension

Protein contaminates: 0.16%; Purified gum had less surface activity than crude one; The crude gum had lower intrinsic viscosity and radius of gyration than the purified and protein free gums; The molecular weight of FSG increased with removing the attached proteins.

The interfacial activity of purified gum was more than other galactomannans.

In a study conducted by Youssef, Wang, Cui and Barbut [7], the molecular weights of crude, purified, and protein free FSG were reported 1.49 × 106 g/mol, 2.28 × 106 g/mol and 2.35 × 106 g/mol, respectively. The authors demonstrated that the highest polydispersity index was related to crude and purified FSG, whereas the lowest was related to protein-free FSG. The molecular weight of purified FSG reported by Youssef, Wang, Cui and Barbut [7] is higher than that reported by Brummer, Cui and Wang [21]. This difference has been related to the enzyme impurity used in Youssef, Wang, Cui and Barbut [7].

FSG is a galactomannan polysaccharide, composing of a linear chain of mannose connected by β-(1 → 4) glycosidic interactions, with galactose substitution at the position of C-6 (Fig. 1) [37]. 4. Physical properties Some physical properties of FSG are given in Table 4. Bulk density, specific gravity, pH, refractive index and specific rotation of FSG were found to be 3.543 (g/mL), 0.997, 6.0–7.9, 1.3368 and +31.6, respectively. Polymers with a linear mannan like native cellulose are

Table 2 Chemical composition of crude FSG, purified FSG and protein free FSG. Gum Youssef, Wang, Cui and Barbut [7] Crude FSG Purified FSG Protein free FSG El-Mahdy and El-Sebaiy [77] Purified FSG

Protein (%)

Rhamnose (%)

Arabinose (%)

Galactose (%)

Glucose (%)

Mannose (%)

G/M ratio

3.74 ± 0.03 1.10 ± 0.0.02 0.16 ± 0.02

0.16 ± 0.00 0.00 0.00

0.54 ± 0.04 0.00 0.00

26.22 ± 0.02 33.91 ± 0.01 32.87 ± 0.02

0.64 ± 0.01 0.00 0.00

31.40 ± 0.03 41.57 ± 0.01 41.84 ± 0.01

0.83 0.81 0.78

18.18

0

25.1

10.7

3.3

22.1

0.48

D. Salarbashi et al. / International Journal of Biological Macromolecules 138 (2019) 386–393

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Table 3 Molecular properties of FSG. Average molar mass moments (g/mol)

Polydispersity

Mw

Mn

Mz

Mp

5.619 × 105

4.831 × 105

5.797 × 105

5.624 × 105

Reference

Mw/Mn

Mz/Mn

1.163

1.200

Wei, Lin, Xie, Xu, Yao and Zhang [34]

completely insoluble in water. As mentioned above, FSG is containing galactose substitution which prevents polymer chains from associating intimately, and as a result, making it completely soluble in cold water [37]. Surprisingly, it has been reported that FSG is the most soluble of the seed gums, however; due to the absence of electrostatic charge on the FSG molecule, the hydration of this polymer is slower than many gums. FSG has a cream color and strong unpleasant flavor which limits its application in bakery products. Ralet, Thibault and Della Valle [38] observed that this unpleasant flavor can be successfully removed by extrusion cooking. Therefore, it can be suggested that extruded FSG can be used to produce baker products without the flavor of FSG.

concentration on Z-average values [42]. The charge of polymers (both anionic and cationic) is mainly dependent on the presence of charged functional groups in their structure. A low value of zeta potential in FSG is due to the neutral structure of this galactomannan. From the data in Table 4, it is evident that when the gum concentration increased, the conductivity significantly influenced (p b 0.05). This increasing trend could be attributed to the presence of electrolytes in the solution, which can change the dispersion's stability.

5. Colloidal dispersion properties

Based on the literature, the emulsifying activity of polysaccharides is related to the presence of a small amount of protein in their composition [43]. This small amount of protein has more tendency to be adsorbed at the oil-water interface and formed a stabilizing layer around oil droplets [44]. The surface activity of FSG was evaluated by Garti, Madar, Aserin and Sternheim [20]. The authors indicated that FSG could decrease surface tension. Surprisingly, the interfacial activity of FSG was better when compared to the other galactomannans. In a research conducted by Youssef, Wang, Cui and Barbut [7], the surface activates of crude, purified and protein free FSG were examined. They found that the surface activity of crude FSG was considerably higher than purified FSG and slightly higher than protein-free FSG. The protein content of crude FSG (3.74%) was lower than those of purified FSG (1.10%) and protein-free FSG (0.16%). Therefore, it can be concluded that the surface activity of FSG is mainly related to the presence of protein components in FSG. It has been reported that with increasing of FSG concentration, up to a certain point, surface tension decreased, but after that, the surface activity of FSG increased [7]. The same observation has been reported by Brummer, Cui and Wang [21], which is opposite of the results reported by Garti, Madar, Aserin and Sternheim [20] who demonstrated that the proteins did not affect the surface activity of FSG.

For FSG, the colloidal dispersion with concentration of 0.01 to 0.2% (w/v), the values of Zeta potential, conductivity and Z-average diameter are presented in Table 4. Zeta potential is commonly used as an indicator for the stability of disperse systems. If the absolute values of zeta potential become higher, the repulsion between polymer macromolecules will be stronger; this results in more stability of the dispersion. Generally, a zeta potential value of higher than 30 (either positive or negative), demonstrates a stable colloidal dispersion [39,40]. As it is presented in Table 4, all dispersions of FSG solutions with different concentrations have negatively charge, with zeta potential values in the range of −20.4 to −14.8 mV, which are greater than that reported for locust bean gum as a galactomannan gum [41]. When the FSG concentration increased from 0.01 to 0.2%, the zeta potential value decreased from −20.4 to −16.93 mV. Therefore, it is expected that with the increase of FSG concentration, the aggregation is increased, and in turn, the particle size of dispersion will be increased. It can be seen that by following an increase in FSG concentration from 0.01 to 0.2%, the polymer size of the dispersion increased from 761.13 nm to 2807.33 nm. The same results have reported for the effect of galactomannan

6. Functional properties 6.1. Emulsifying properties

Fig. 1. The chemical structure of fenugreek seed gum [37].

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Table 4 Polymer size, polydispersion index and Zeta potential of FSG dispersion [10]. FSG concentration (%)

Zeta potential (mV)

Conductivity (ms/cm)

0.01 0.02 0.05 0.1 0.2

−20.40 ± 3.20 −20.26 ± 0.97 −16.1 ± 0.97 −14.80 ± 1.74 −16.93 ± 0.58

0.0248 ± 0.0006 0.0262 ± 0.0013 0.0481 ± 0.0013 0.0922 ± 0.0001 0.1703 ± 0.0005

z-Average diameter (nm) 761.13 ± 64.89 860.33 ± 59.25 1139.33 ± 64.60 1767.66 ± 36.14 2801.33 ± 6.47

According to literature, extrusion cooking of proteins and polysaccharides results in improvement of their emulsifying capacity [45]. This effect is due to unfolding of the protein molecules which results in exposing their hydrophobic functional groups from the inside, and consequently enhancement of the emulsifying capacity of proteins [24]. However, Chang, Cui, Roberts, Ng and Wang [24] indicated that the emulsification capacity of extruded and non-extruded FSG was approximately similar which could be associated with the mild process conditions used. These mild extrusion process conditions were not enough to change the structure of proteins and improve the emulsifying ability of FSG. Hence, more sever extrusion conditions should be used to improve the emulsifying properties of FSG. The effect of ultra-sonication (US) and high shear rate (HS) on the emulsifying properties of fenugreek galactomannans were investigated by Kaltsa, Yanniotis and Mandala [46]. It was observed that the droplet size of emulsion was maximum in the absence of FSG. When the gum incorporated into emulsion formulation, the droplet size significantly decreased. This effect has been attributed to the viscosity improvement of continues phase which led to the immobilization of droplet, and consequently provide more time for adsorbing proteins and stabilizing droplet [46,47]. The authors also indicated that unpurified FSG had more ability to decrease the droplet size when compared to commercial galactomannans such as locust bean gum and guar gum, whereas the purified polysaccharide had higher viscosity and led to the formation of emulsion with highest stability. Following an increase in FSG concentration, the emulsion stability improved which is related to viscosity improvement at higher gum concentration. Comparatively, the droplet size of the emulsion prepared by US method was smaller than HS method one. In conclusion, FSG can be introduced as a viable alternative to guar gum and locust bean gum. The interaction between polysaccharides and proteins is commonly led to the improvement of emulsifying stability of processed foods. This interaction occurs between amino groups in the proteins and carboxyl groups present in the polysaccharide structure [1]. Kasran, Cui and Goff [1] and Kasran, Cui and Goff [48] compared the emulsifying ability of BSF and covalent attachment of FSG to soy whey protein isolate (SWPI). The authors reported that after 3 days of storage at 60 °C, the particle size and polydispersity index of the FSG-SWFI coacervate were enough to produce oil in water emulsion with small droplet size. They also found that the emulsifying ability of coacervate fabricated by partially hydrolyzed FSG-SWPI was less than that fabricated by unhydrolyzed one. It also demonstrated that the heating of conjugates solution before emulsifying process led to the enhancement of their emulsifying capacity.

6.2.1. Steady-state rheological behavior 6.2.1.1. Effect of concentration. In a study [34], the steady flow behavior of FSG solutions as a function of polymer concentration (0.05–2.0% (w/v)) was investigated. It was observed that as the shear rate increased, the magnitude of viscosity decreased, exhibiting a shear thinning behavior for FSG solutions. This behavior was expectable for FSG and other galactomannans [18,50,51]. The shear thinning behavior of galactomannans is related to the disentanglement of polymer chains in the direction of flow [52]. Furthermore, this behavior has been attributed to the alignment of polymer chains in the direction of flow which led to fewer polymer chains interaction [53]. The time-dependent flow behavior of FSG solutions also was evaluated by Wei, Lin, Xie, Xu, Yao and Zhang [34]. Time-dependent behavior of polymer solution is arisen from the changes happen in the inner structure of fluid [52]. Different methods have been developed to evaluate the thixotropic property of hydrocolloids. For instance, the area of hysteresis loops can be used as an indicator to determine the degree of time depending behavior of the gum solutions. A larger area indicates a stronger timedependent property. Moreover, Benchabane and Bekkour [52] developed a model to determine the degree of thixotropy of FSG solutions (Eq. (1)): a¼

A1 −A2  100 A1

ð1Þ

where, α, A1 and A2 are thixotropic index (dimensionless), and the areas under the up and down curves, respectively. Wei, Lin, Xie, Xu, Yao and Zhang [34] observed that when the FSG concentration increased from 0.05 to 2% (w/v), the values of α increased from 0.6 to 5.7, indicating a more time dependency at higher polymer concentrations. This effect has been attributed to the increase of interparticle friction and collision by increasing gum concentration, which results in the increase of viscous forces and consumption of energy in the FSG [54]. Another finding [10] demonstrated that the viscosity of FSG solution (at a constant shear rate of 10 rpm) increased from 32 mPa·s to 12,200 mPa·s when the gum concentration increased from 0.25% to 2%. The authors indicated that the Power-law model could successfully describe the rheological data of FSG solution. As expected, they reported that an increase in FSG concentration was accompanied by an increase in k value, which is in agreement with those reported by other studies. 6.2.1.2. Effect of temperature. In a study conducted by Işıklı and Karababa [9], the effect of various temperatures (10–30 °C) was evaluated. It was observed that in all tested temperatures, the backward curves were higher than forwarding ones, demonstrating time-dependent behavior (rheopectic) (Fig. 2). In rheopectic fluids, the polymeric structure

6.2. Rheological behavior The viscosity of hydrocolloids is an indicator for their capacity to act as stabilizer, emulsifier and suspending agent [25]. Various factors such as polymer concentration, temperature, shear rate and presence of salts and sugars reported changing the rheological properties of hydrocolloid solutions [49].

Fig. 2. Hysteresis loop of the flow curves of FSG solutions at various temperatures [9].

D. Salarbashi et al. / International Journal of Biological Macromolecules 138 (2019) 386–393

becomes more regular by increasing the time of shearing. The authors used three common models; power law, Herschel–Bulkley, and Casson to describe the flow behavior of FSG solutions. It was observed that the power law model was the best model for fitting the rheological data. Işıklı and Karababa [9] determined the consistency coefficient (k) and flow behavior index (n) of FSG solution as a function of temperature. They observed that an increase in temperature was accompanied by an increase in the value of k. k is an indicator of the thickening properties of gum solutions. The thickening properties of hydrocolloids solution are generally decreased with the increase of solution temperature. This inspected that the behavior of FSG solutions may be attributed to the improvement of FSG water solubility at higher temperatures and decrease of the ratio of galactose/mannose in the aqueous suspension of FSG powder [9]. The same observation has been reported by GarciaOchoa and Casas [55], who showed that by increasing the temperature, the apparent viscosity of locust bean gum solutions decreased. Arrhenius equation is commonly used to evaluate the temperature sensitivity of polymer solutions (Eq. (2)). Higher activation energy indicated a more temperature sensitivity. −Ea k ¼ k0 exp RT

ð2Þ

where, k0 is Arrhenius constant (s−1), Ea is activation energy (kJ/mol), R is universal gas constant and T is absolute temperature (k). Işıklı and Karababa [9] indicated that the magnitude activation energy for forwarding flow curve was higher than that obtained from a backward curve, revealing forward cure had more temperature stability than the backward curve. 6.2.1.3. Effect of ultra-sonication. Various studies have evaluated the effect of high shear rate processing such as ultrasonication on steadystate properties of hydrocolloids [46,56,57]. In a recent study, the influence of ultrasonication on the flow behavior of FSG was investigated [46]. They indicated that with applying the ultrasonication process (70% energy for 1 min), the apparent viscosity of FSG solution was decreased by two-fold. The authors reported that after the ultrasonication process, the solution temperature increased from 25 to 47 °C. The increase in temperature is due to the increase of scission reaction [58]. With the increase of solution temperature, the stability of hydrogen bonds between polymer and solvent molecules decreases, and consequently the solution viscosity decreases [59,60]. With further increase of sonication time up to 3 min, a considerable decrease in apparent viscosity was reported. It has been reported that when the sonication time increases to 3 min, the molecular weight of gum decreased by 50%. The molecular weight of polymers has a profound effect on thickening properties [61]. Hence, the remarkable reduction of the apparent viscosity of FSG after 3 min sonication may be related to the decrease of FSG molecular weight. 6.2.2. Dynamic rheological behavior 6.2.2.1. Effect of polymer concentration. The dynamic viscoelastic properties of FSG solutions as a function of gum concentration (0.05%–2.00%) was investigated by Wei, Lin, Xie, Xu, Yao and Zhang [34]. At lowfrequency range, the gum solution with a concentration of 0.05% showed a viscous-like behavior, but by increasing the frequency, FSG behaved as a gel. On the other hand, the gum solutions with the polymer concentration of N0.05%, exhibited a gel-like behavior. In another study Youssef, Wang, Cui and Barbut [7] evaluated the effect of different gum concentration (0.5, 1 and 2%) on the viscoelastic properties of FSG. In opposite with that reported by Wei, Lin, Xie, Xu, Yao and Zhang [34], Youssef, Wang, Cui and Barbut [7] reported that FSG solutions had viscous-like behavior, where loss modulus was higher than storage modulus at low frequency and the reverse was reported at high frequency.

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6.2.2.2. Effect of temperature. Due to the encountering of the foods containing hydrocolloids with an extensive range of temperature, evaluation of temperature stability of hydrocolloids is important to explore their potential application in the food industry [62]. Literature review revealed that galactomannans have low-temperature stability. For instance, it has been reported when the temperature increased from 20 to 80 °C, the apparent viscosity of galactomannans reduced by 50% [63]. Wei, Lin, Xie, Xu, Yao and Zhang [34] evaluated the influence of temperature range of 0 to 80 °C on viscoelastic properties of FSG. Surprisingly, the authors observed that at all concentrations and temperatures tested, storage modulus was greater than loss modulus, indicating FSG solutions remained in the gel-like state. Temperaturesensitivity of FSG solution was concentration-dependent. For all tested concentration, except for 1.5%, with increasing gum solution temperature, the magnitude of storage modulus decreased. This decreasing trend is associated with a reduction of intermolecular interaction which decreases the energy needed to flow [18]. Surprisingly, for the FSG solution with a concentration of 1.5%, when the temperature of gum solution increased from 0 to 30 °C, storage modulus decreased, but with further increasing the temperature, storage modulus begun to increase. This effect has been attributed to the formation of a structure with the three-dimensional network at high temperature. 6.3. Hydration properties The physical appearance of FSG dispersion after 10 min stirring extruded and non-extruded is presented in Fig. 3. It can be seen that in the non-extruded FSG solution, fish-eyes appears (Fig. 3-B). On the other hand, the extruded sample was dispersed very well (Fig. 3-A). This result is reliable with those reported for other polysaccharides such as xanthan gum [64], sugar beet pulp [65], pea hulls [66], apple pomace [67] and wheat bran [38]. As expected, the authors also reported that when the solution temperature increased from 105 to 150 °C, the water solubility of the extruded FSG increased from 33.4% to 51.3%. In order to evaluate the water holding capacity (WHC) of extruded and non-extruded FSG, Ralet, Thibault and Della Valle [38] plotted the absorbed water versus time. In this plot, the water absorbed content at equilibrium is considered as WHC. The authors observed that the WHC of extruded FSG was not significantly different from and non-extruded FSG. It also was found that highest water dispensability, WHC and water solubility of FSG were obtained for the extruded FSG at a temperature of 150 °C. In conclusion, according to literature, the extrusion process at sever condition can lead to improving the water dispensability, WHC and water solubility of FSG. 6.4. Oil holding capacity (OHC) Different factors such as protein content, surface area, porosity and capillary attraction affect the OHC of polysaccharides [68,69]. Kaltsa, Yanniotis and Mandala [46] compared the OHC of FSG to other galactomannans like guar gum and locust bean gum. The OHC for FSG, guar gum and locust bean gum were found to be 47.37, 77.59 and 138.02 (g/100 g gum), respectively. As mentioned above, protein is one of the most important factors affecting OHC. The protein contents of FSG, guar gum and locust bean gum are as follow: FSG = 1.97 (% wt), guar gum = 3.92 (%wt) and locust bean gum 6.43 (%wt). Pearson test demonstrated that there is a positive correlation between protein content of these hydrocolloids and their oil holding capacity. 6.5. Construction of edible films From an environmental point of view, the uses of plastics have led to several environmental problems for plants, animals, and human [70]. Therefore, trends to the application of novel, eco-friendly, and biocompatible packages are so promising [71].

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Fig. 3. The physical appearance of FSG dispersion after 10 min stirring. A) Extruded FSG; B) non-extruded FSG [24].

Nieto [37] prepared an eco-friendly film using a 3% FSG solution by casting method. The thicknesses of the developed films were, on average, of 40 mm (0.4 in.). From a mechanical point of view, the values of the tensile strength (TS) and puncture of strength were 2330 g and 230 g, respectively. It has been reported that FSG based films had the weakest film structure compared to other seed gums because of its relatively denser galactose substitution, that act a stronger hindrance to inter-polymer chain association. In recent years, various techniques have been employed to improve the physicochemical characteristics of biodegradable films. For instance, incorporating nanoparticles such as TiO2, SiO2, and Ag+, and Nano-clays to reinforce and improve the film's properties. In a recent study, Memiş, Tornuk, Bozkurt and Durak [72] incorporated different nanoparticles (Na+ montmorillonite (MMT), halloysite (HNT) and Nanomerto (NM)) into FSG matrix, and then evaluated the physicochemical properties of fabricated nanocomposites. Following an increase in the nanoclay concentration, oxygen barrier ability and thermal properties of the developed nanocomposites significantly improved (p b 0.05). Agar diffusion tests were used to investigate the antimicrobial activity of the nanocomposites. It was observed that the developed films had excellent antimicrobial activity against Listeria monocytogenes, Escherichia coli O157:H7, Staphylococcus aureus and Bacillus cereus. The films constructed by FSG (5%) nanoclay showed higher TS, but the value of elongation at break (EB) of the pure film decreased with the increase of nanoclay concentration. SEM analysis demonstrated that in all developed nanocomposites, nanoparticles reinforcements provided a homogeneous and smooth structure. Overall, FSG based edible nanocomposites can be introduced as a good packing system, especially for antimicrobial food packaging applications. 7. Biological activity Antioxidant capacity and anti-fungi activity of fenugreek polysaccharide with different molecular weights were investigated by Wu, Yan, Zhang, Miao, Lu and Wu [73]. The authors indicated that both acidolysis and enzymolysis products of the gum had a considerable anti-hydroxyl radical (OH) and superoxide anion activities. Furthermore, the hydrolyzed products had clear anti fungi effect on Botrytis

cinerea, F. moniliforme, Ascochyta fabae speg and Eggplant Verticillium wilt. They also found that Enzymolysis products had more antioxidant and antimicrobial activity than acidolysis ones. In another study [74], promising but inconsistent anti-hyperglycemic activity was reported for the galactomannan obtained from fenugreek seeds. They observed that the polysaccharide of fenugreek seeds had anti-hyperglycemic activity against alloxan-induced hyperglycemia without body weight gain. The polysaccharides also could protect mice pancreas from alloxan-induced histological changes. The influence of galactomannan polysaccharide obtained from fenugreek seeds on the level of blood glucose of the normal and alloxan diabetic rats was evaluated by Khatir, Ding and Fang [75]. They indicated that FSG reduced blood glucose both in normal and diabetic rats which were in agreement with those observed by Jianxin [76] who indicated that FSG reduced the effect of hyperglycemia. 8. Conclusion FSG is mainly composed of galactose and mannose, suggesting a galactomannan-like structure. The modified FSG like extruded FSG had more hydration than non-extruded FSG.FSG has high viscosity at low concentration, which indicated that it can be used as an excellent stabilizer and thickener. The film fabricated by FSG showed good physic-mechanical properties. From a biological point of view, FSG can be used as antioxidant and anti-fungi agent in food systems. FSG has an excellent emulsification capacity, which enables its application in the food, cosmetic and/or pharmaceutical industries. 9. Future trends and perspective Fenugreek is a leguminous plant that is extensively used in the medicinal, pharmaceutical and nutraceutical fields. The literature review demonstrated that the galactomannan obtained from fenugreek seeds (FSG) has good potential to act as an emulsifier, stabilizer, and thickener. As mentioned above, there is no technique that can successfully remove the attached protein from FSG. A future challenge is required to use of various isolation methods, purifications and other processing conditions to remove the attached protein to FSG. Furthermore, taken

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