Galactomannans

Galactomannans are found in a great number of plants, many of which are of considerable pharmaceutical interest. The importance of galactomannans and their biochemistry has been reviewed by Whistler 20) and by Dey 21). 

The common molecular structure consists of 1,4-linked p-D-mannopyranosyl units to which varying amounts of a-D-galactopyranosyl groups are joined (Fig. 9). 

The linear, but highly branched, molecular structure of the galactomannans is the reason for some specific properties which are quite different from those of the unbranched cellulose-like and water-insoluble mannans and glucomannans. Galactomannans are hydrated in cold water and give stable solutions even in acidic formulas. The interactions of galactomannans with other polysaccharides are the base of a variety of industrial applications. 

It has been known for some time that pectin reduces the level of cholesterol in the blood, and, more recently, a similar effect has been described for several galactomannans. They are also very useful in the treatment of diabetes as it has been shown by Jenkins et al. 24). 

The seeds of Tamarindus indica contain polysaccharides which can be extracted with hot water and purified by precipitation with alcohol. The polysaccharide is composed of D-galactose, D-xylose, and D-glucose (Fig. 10). These xyioglucans have been named amyloids since they give a color reaction with iodine similar to starch. The xyioglucans from Tamarindus are gel-forming polysaccharides which are stable in a wide pH range. This type of polysaccharide is mainly used in food industry, but, in some cases, it has been pharmaceutically employed as a substitute for pectin. 

The highly branched GaM of Mimosa seeds, isolated by a scaled-up process [186] at a yield of 20% of seed weight, showed a Man Gal ratio of 1.1 1 and structural features of the gum obtained on a laboratory scale [ 183]. Based on C-NMR spectroscopy of GaM from Cassia angustifolia [179], with a Man Gal ratio of 2.9 1, a blockwise pattern of the galactosyl branches was suggested. 

The slightly galactosylated mannans are essentially linear polymers. As a result of their cellulose-like (1 4)-/3-D-mannan backbone, they tend towards self-association, insolubility, and crystallinity. Crystallographic study of C. spectabilis seed GaM [180] with a Man Gal ratio 2.65 1 suggested an orthorhombic unit cell with lattice constants of a = 9.12, b = 25.63, and c = 10.28 the dimension b was shown to be sensitive to the degree of galactose substitution and the hydration conditions [180 and references therein, [191]]. 

Mannans free of galactosyl side chains are rather rare. Slightly galactosylated mannans 4% galactose), considered as linear 4)-D-mannans, have 

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Locust Bean Gum. Locust bean gum [9000-40-2], also known as catob seed gum, is a galactomannan extracted from the endosperm of the catob tree seed which is cultivated in the Mediterranean area. The primary use of locust bean gum is in dairy appHcations such as ice cream. It is often used in conjunction with carrageenan because the chemical stmctures of the two enable them to cross-link and form a gel (85). 

Gelled Explosives. Aqueous solutions of water-dispersible, nonionic, natural hydroxylated polymers, such as galactomannans and their derivatives, can be cross-linked with organic titanates, such as TYZOR TE, TYZOR AA, and TYZOR LA to give water-bearing gels, which can be used to formgeUed explosives (532—534). 

Polymer chains of guar gum and its derivatives, in fact of all galactomannans, are readily cross-linked with borate and titanium ions. Gels formed in this way are mbbery in nature. 

Less polysaccharide can also be used in products by taking advantage of the synergistic gelling of xanthan/galactomannan mixtures which forms thermoreversible gels at lower concentrations than if each is used separately. 

Fig. 38.—Stereo view of three turns of the 2-fold galactomannan (45) helix containing galactose side-chains on alternate mannose residues. In this conformation, the side chains are turned up toward the non-reducing end, and the backbone is stabilized by intrachain hydrogen bonds. The helix axis is represented by the vertical line.

Galactoglucan, 362-364, 417-418 Galactomannans, 395-396 y-radiation, effects on saccharides, 17 Gellan, 385 - 391... 

Equation 11 has been popularly used for example to investigate the molecular weights of carboxymethylchitins [51-53], glycodendrimers [54,55], galactomannans [56], beta-glucans [57,58] and alginates [59]. 

Evans, A.J. Hood, R.L. Oakenfull, D.G. Sidhu, G.S. (1992). Relationship between structure and function of dietary fibre a comparative study of the effects of three galactomannans on cholesterol metabolism in the rat. British Journal of Nutrition, Vol.68, No.l, (July 1992), pp. 217-229, ISSN 0007-1145. 

Morris G.A., Patel T.R., Picout D.R., Ross-Murphy S.B., Ortega A., Garcia de la Torre J., Harding S.E. 2008. Global hydrodynamic analysis of the molecular flexibility of galactomannans. Carbohydrate Polymers 72, 356-360. 

Three related galactomannans have been studied as films to 140 nm. These polysaccharides have a (1 4)-jS-D-mannopyranosyl backbone with (l- 6)-a-D-galactopyranosyl substituents (see formula 4). 

Fig. 11.—Circular Dichroism Spectrum for a Solid Film of Guar Galactomannan. (Redrawn from Ref. 24.)...

Guar gum is a galactomannan used like locust bean gum and at approximately the same levels. However, unlike locust bean gum, it swells in cold solution and requires no heat for complete hydration. It also induces mix separation which may be controlled with carrageenin. It is well suited for use in HTST systems. 

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