11.2 Galactomannan: The Chief Constituent
of Fenugreek Gum
11.2.1 Structural Properties
Galactomannan is the chief constituent of fenugreek seeds composed of b-(1,4)-Dmannose and a-(1,6)-D-galactose subunits (Cerqueira et al. 2011). It is extracted
from fenugreek seeds and have an approximately equal number of mannose and
galactose residues which makes it readily soluble in water. Generally, the existence
of 180-190 number of monosaccharides (both galactose and mannose) provide a
molecular weight of approximately 30 KDa to this natural polymer (Prajapati et al.
2013a, b). The backbone of galactomannan consists of 90–95 residues of b-1,4
linked mannopyranosyl units and each backbone monomer comprise an a-1,6
linked galactopyranosyl unit (Prajapati et al. 2013a, b). X-ray diffraction studies
show the orthorhombic lattice of hydrated fenugreek gum with a, b and c value of
0.912 nm, 3.335 nm and 1.035 nm, respectively (Song et al. 1989). Gas
chromatography-mass spectroscopy (GC-MS) studies of partially methylated
alditol acetates gum extracted from fenugreek showed it to be a polysaccharide
consists of 1,4 linked mannose having partially substituted galactose at C6 position
(Brummer et al. 2003).
1 H NMR and
13 C NMR studies elucidated the structural
characteristics of galactomannan and showed that it consists of b-(1,4)-linked Dmannopyranose and a-(1,6)-linked D-galactopyranose. Although the ratio of
mannose to galactose residues varies from species to species, it was observed that
the polymer backbone consists of mannose residues and about 83% of backbone is
substituted by galactose at C6 position of mannose. Coupling constant analysis
revealed that D-mannose and D-galactose possess b and a linkage, respectively
(Jiang et al. 2007) (Fig. 11.1).
11.2.2 Physicochemical Properties
Galactomannans extracted from the fenugreek seeds are neutral polysaccharides
with highly substituted galactose residues on mannose backbone (Jiang et al. 2007;
Cui 2001; Hefnawy and Ramadan 2011). Extremely branched structure and high
molecular weight of fenugreek gum are responsible for its lower viscous nature
among other industrially used gums such as locust bean gum and guar gum
(Brummer et al. 2003, Jiang et al. 2007; Cui 2001). Fenugreek gum solution
appears to be more transparent than the guar gum solution due to the presence of
less water insoluble constituents (Jiang et al. 2007). The higher degree of galactose
substitution on the mannose backbone has been claimed as the prime reason for this
behaviour (Brummer et al. 2003). Viscosity of aqueous fenugreek gum solution
depends upon shear stress, temperature and concentration (Wei et al. 2015).
Increase in the fenugreek gum concentration enhances the viscosity of solution
11 Pharmaceutical and Therapeutic Applications of Fenugreek Gum
383
of Fenugreek Gum
11.2.1 Structural Properties
Galactomannan is the chief constituent of fenugreek seeds composed of b-(1,4)-Dmannose and a-(1,6)-D-galactose subunits (Cerqueira et al. 2011). It is extracted
from fenugreek seeds and have an approximately equal number of mannose and
galactose residues which makes it readily soluble in water. Generally, the existence
of 180-190 number of monosaccharides (both galactose and mannose) provide a
molecular weight of approximately 30 KDa to this natural polymer (Prajapati et al.
2013a, b). The backbone of galactomannan consists of 90–95 residues of b-1,4
linked mannopyranosyl units and each backbone monomer comprise an a-1,6
linked galactopyranosyl unit (Prajapati et al. 2013a, b). X-ray diffraction studies
show the orthorhombic lattice of hydrated fenugreek gum with a, b and c value of
0.912 nm, 3.335 nm and 1.035 nm, respectively (Song et al. 1989). Gas
chromatography-mass spectroscopy (GC-MS) studies of partially methylated
alditol acetates gum extracted from fenugreek showed it to be a polysaccharide
consists of 1,4 linked mannose having partially substituted galactose at C6 position
(Brummer et al. 2003).
1 H NMR and
13 C NMR studies elucidated the structural
characteristics of galactomannan and showed that it consists of b-(1,4)-linked Dmannopyranose and a-(1,6)-linked D-galactopyranose. Although the ratio of
mannose to galactose residues varies from species to species, it was observed that
the polymer backbone consists of mannose residues and about 83% of backbone is
substituted by galactose at C6 position of mannose. Coupling constant analysis
revealed that D-mannose and D-galactose possess b and a linkage, respectively
(Jiang et al. 2007) (Fig. 11.1).
11.2.2 Physicochemical Properties
Galactomannans extracted from the fenugreek seeds are neutral polysaccharides
with highly substituted galactose residues on mannose backbone (Jiang et al. 2007;
Cui 2001; Hefnawy and Ramadan 2011). Extremely branched structure and high
molecular weight of fenugreek gum are responsible for its lower viscous nature
among other industrially used gums such as locust bean gum and guar gum
(Brummer et al. 2003, Jiang et al. 2007; Cui 2001). Fenugreek gum solution
appears to be more transparent than the guar gum solution due to the presence of
less water insoluble constituents (Jiang et al. 2007). The higher degree of galactose
substitution on the mannose backbone has been claimed as the prime reason for this
behaviour (Brummer et al. 2003). Viscosity of aqueous fenugreek gum solution
depends upon shear stress, temperature and concentration (Wei et al. 2015).
Increase in the fenugreek gum concentration enhances the viscosity of solution
11 Pharmaceutical and Therapeutic Applications of Fenugreek Gum
383