Polysaccharides

Lichenin, the poly β-D-Glucan of Cetraria islandica (Iceland moss), is found by enzymic degradation to differ in fine structure from the poly β-D-glucans of cereal grains. Thus, the basic structure of lichenin is a tetrameric unit in which two adjacent 1,4 linkages alternate with an isolated 1,3 linkage; occasionally four consecutive monomers are linked by 1,4 bonds. The immunomodulatory activity of isolichenan was tested in in vitro phagocytosis and anti-complementary assays, and proved to be active in both cases.
The image was kindly provided by Prof Mike Guiry from Cork who runs ‘The Seaweed Site’.

Glycogen is a highly branched polysaccharide of glucose that serves as a form of energy storage in animals and fungi. It is the main storage form of glucose in the body.  In humans, glycogen is made and stored primarily in liver and muscle cells and functions as the second most important energy storage molecule to fat which is held in adipose tissue. Glycogen is analogous to starch and has a structure similar to amylopectin, but is more extensively branched and compact than starch. It occurs as granules in the cytosol/cytoplasm in many cell types, and plays an important role in the glucose cycle.

Arabinoxylans consist of α-L-arabinofuranose residues attached as branch-points to β-(1,4)-linked D-xylopyranose main chains. These may be 2- or 3-substituted or 2- and 3- di-substituted. The arabinose residues may also be linked to other groups attached such as glucuronic acid residues, ferulic acid cross links and acetyl groups. Arabinoxylans generally consist of between 1500 - 5000 residues.

Gum karaya is exuded from Sterculia urens, a bushy tree found in dry regions of North India. Due to its extensive swelling capacity in water it is used as a laxative and as a denture adhesive. The structure consists of D-galactose, D-glucuronic acid and L-rhamnose but the detailed molecular structure is still incompletely known.

Dextran is α-(1,6)-linked α-D-glucan produced by fermentation of Leuconostoc mesenteroides via the action of the enzyme dextransucrase on sucrose. The main use for native dextran is as a blood plasma extender in blood transfusions. A complex of iron with dextran, known as iron dextran, is used as a source of iron to baby piglets which are often anaemic at birth.

Water thickener; rheological control additive; has industrial appplications

Larch arabinogalactan is extracted from the heartwood of the western larch Larix occidentalis. This compound has a backbone of 1,3-linked β-D-galactopyranosyl units each of which contains a side chain at position C-6. Arabinogalactans are used as emulsifiers, stabilizers and binders in the food, pharmaceutical and cosmetic industries, as low viscosity dietary fibres and as a prebiotic fibres.

Oat β-glucans are water-soluble β-glucans derived from the endosperm of oat kernels, which contain β-1,3 and β-1,4 linkages. They are known for cholesterol lowering and hypoglycemic properties, as well as their use in various cosmetic applications. Recent research has shown their potential application in immunomodulation and wound healing.

Dermatan sulphate is a glycosaminoglycan found in skin, blood vessels, heart valves, tendons, aorta, spleen and brain and is usually isolated from pig skin or beef lung tissue. The disaccharide repeat unit is composed of L-iduronic acid and N-acetyl-galactosamine-4-sulphate linked β-(1,3) and β-(1,4). There are also small amounts of D-glucuronic acid.

Methyl cellulose is a water-soluble polymer that is used as a binder or thickener in pharmaceutical, food, and ceramic processing applications. Methylcellulose has an unusual lower critical solution temperature (LCST) between 40 °C and 50 °C. At temperatures below the LCST it is readily soluble in water; above the LCST it is not soluble, which has a paradoxical effect that heating a saturated solution of methylcellulose will turn it solid, because methylcellulose will precipitate out. The temperature at which this occurs depends on DS-value, with higher DS-values giving lower solubility and lower precipitation temperatures because the polar hydroxyl groups are masked.

Dextran is α-(1,6)-linked α-D-glucan with α-(1,3)-linked glucose branch points produced by fermentation of Leuconostoc mesenteroides via the action of the enzyme dextransucrase on sucrose.  The main use for native dextran is as an extender in blood transfusions and products having a range of sharp cut-off molecular weights are produced commercially for this and other applications. A complex of iron with dextran, known as iron dextran, is used as a source of iron for baby piglets which are often anaemic at birth.

Carboxymethyl curdlan is widely used in the preparation of nanoparticles for biomedical applications. Following the synthesis of superparamagnetic iron oxide nanoparticles (SPIN) capped with carboxymethyl curdlan for use in cellular and in vivo imaging applications, the stability and dispersibility of SPIN in water were greatly improved with the introduction of the carboxymethyl curdlan moiety. Recently, a green and simple route was proposed to synthesize Ag nanoparticles using carboxymethylcurdlan under UV irradiation.

Konjac glucomannan is an acetylated (1,4)-β-D-glucomannan obtained from the tubers of Amorphophallus konjac or Konnyaku root. It is widely used in foods, pharmaceuticals paints and explosives. It has been shown that ternary mixtures of konjac glucomannan, xanthan gum and sodium alginate can form a non-covalently linked complex which exhibits enhanced rheological properties of value in, for example, functional foods.

The main cell-wall components of baker’s yeast (Saccharomyces cerevisiae) as well as β-glucan are mannans with an α-1,6 mannose backbone and α-1,2 and α-1,3 mannose branches.
The image was kindly provided by Dr. Chris Lawson.

Starch consists of two polysaccharides, amylose and amylopectin and represents approximately 20-25% of the total polysaccharide content in starch. Amylose molecules consist of single mostly unbranched chains of 500-20,000 α-(1->4)-D-glucose residues dependent on source (e.g. wheat, rice, potato, tapioca, etc). Amylose can form an extended shape (hydrodynamic radius 7-22 nm) but generally tends to wind up into a rather stiff left-handed single helix or form even stiffer parallel left-handed double helical junction zones. Hydrogen bonding between aligned chains causes retrogradation and releases some of the bound water (syneresis). The aligned chains may then form double stranded crystallites that are resistant to amylases. These possess extensive inter- and intra-strand hydrogen bonding, resulting in a fairly hydrophobic structure of low solubility. The amylose content of starches is thus the major cause of resistant starch formation.

Fucogalactan (GFS) is a polysaccharide isolated and purified from the brown seaweed Undaria pinnatifida. The polysaccharide is a sulphated galactose containing fucan. Fucogalactan is currently under investigation for possible therapeutic indications including anti-inflammatory properties, immuno- modulating activities, inhibition of tumor growth, stem cell replentishment, antiviral activity, dementia and ulcer healing.Fucoidan ≥ 75 %
The image was kindly provided by Prof Mike Guiry from Cork who runs ‘The Seaweed Site’.

Pectins are regarded as linear chains of α-1,4-linked D-galacturonic acid, a homogalacturonan (pectic acid). In the products of commerce, the degree of methylation has a vital influence on the properties of pectin, especially the solubility and gel forming characteristics.

Pectins are regarded as linear chains of α-1,4-linked D-galacturonic acid, a homogalacturonan (pectic acid). In the products of commerce, the degree of methylation has a vital influence on the properties of pectin, especially the solubility and gel forming characteristics. Commercial high methoxy (HM) pectin has > 70% of hydroxyl groups methyl esterified. HM pectin forms gels in the presence of sucrose and for this reason it is used in jams often in combination with other fruits.