Polysaccharides

Furcellaran (Danish agar) is similar to κ-carrageenan but is less sulphated (50%). It has been extracted from Furcellaria lumbricalis, which is mainly harvested off the coast of Denmark. This species, which is common to most parts of Europe, occurs as a loose form and only reproduces vegetatively. The image was kindly provided by Prof Mike Guiry from Cork who runs ‘The Seaweed Site’.

Gum ghatti is an exudate gum from the tree Anogeissus latifolia found in India and Sri Lanka. Applications are similar to Gum arabic in the food and pharmaceutical industries, where it is used as an emulsifier. The polysaccharide is reported to have an extremely complex structure which contains both oligosaccharides and polysaccharide elements. The polysaccharide contains Ara, Gal, Man, GlcA and Rha in a molar ratio of 61:39:6:10:6, a backbone of (1,6)-linked β-D-galactopyranosyl units and side chains of L-arabinofuranose units with some (1,4)-D-glucopyranosyluronic acid units, some joining (1,2)-D-mannopyranosyl units.

Sodium carboxymethyl dextran (CM-dextran) is a white, odourless and tasteless powder, which is freely soluble in water or electrolyte solutions. The product has a pronounced polyanionic character, due to the high degree of carboxyl substitution.  Applications that have been described for CM-dextran include carriers of paramagnetic contrast agents, preparation of conjugates of pharmacologically active compounds and CM-dextrans in biosensors.  A number of other uses in cosmetics, agriculture, foods, paints and textiles have been the subject of patent applications.

Carboxymethyl cellulose is used in food as a viscosity modifier, thickener, to stabilise emulsions and are found in gluten-free and reduced-fat products. It is also a constituent of toothpaste, laxatives, diet pills, water-based paints, detergents, textile sizing, and various paper products.  In laundry detergents, it is used as a soil suspension polymer. It is also used in pharmaceuticals as a thickening agent and in the oil-drilling industry as a viscosity modifier and water-retaining agent.

‘Water kefir’ is a home-made beverage, which was thought to contain significant amounts of bacterial exopolysaccharides. It has now been reported that the exopolysaccharide fraction of this material contains dextrans with similar structures, having a number of (1,3) linkages, branched at positions O3 and position O2 and with a wide range of molecular weights.  In addition, it was shown that a small amount of levan is also present.

Chitosan is the deacetylated form of chitin.  The polysaccharide is deacetylated in order to render it soluble, which is then possible at pH values of less than 7 (normally in dilute acid).  This then allows the material to be used in a number of industrial applications as a binder and film former.

Cellulose acetate phthalate (CAP) finds use in the formulation of pharmaceuticals, such as the enteric coating of tablets or capsules and for controlled release formulations, where it is often used with other coating agents such as ethyl cellulose.  It contains about 50% acetate and 25% as the phthalate ester with the rest as free hydroxyl groups.  Enteric coatings based on CAP are resistant to acidic gastric fluids, but easily soluble in mildly basic medium of the intestine. The pH-sensitive solubility of CAP is mainly determined (as are other properties of this mixed ester) by the degree of substitution and by the molar ratio (acetyl and phthaloyl groups).

DEAE-Dextran (DEAE-D) is a positively-charged dextran derivative that can be used for vaccine production, gene therapy, protein stabilisation, dyslipidemia prevention, flocculating agents, and many other applications. DEAE-D is also used for transfecting animal cells with foreign DNA.  DEAE-Sepharose, DEAE-650 and DEAE-Sephadex are commonly used in chromatography for the separation of biological molecules such as proteins and carbohydrates.

Locust bean (carob) gum is the refined endosperm of the seed of the carob tree, an evergreen of the legume family (Ceretonia siliqua). The tree grows extensively in Spain and is cultivated in many other Mediterranean countries. Locust bean gum, like guar gum, is a galactomannan with a backbone of (1,4) β-D-mannopyranosyl units having branches of (1,6)-linked α-D-galactopyranosyl units. However, locust bean gum has substantially fewer side chains than guar gum and these are clustered in blocks leaving longer regions of unsubstituted mannosyl regions. The gum is only partially soluble in water and suspensions require heating before solubility is achieved. As with guar, the polysaccharide forms gels with other gums such as carrageenan and xanthan. Applications are in the food industry to enhance texture, in paper making and in the textile industry.