Polissacáridos

Xanthan gum is a polysaccharide produced by the Gram negative bacteria Xanthomonas campestris. It has unique rheological and gel forming properties and finds many applications particularly in the food and oil industries. Recently, 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 structure of xanthan is based on a cellulosic backbone of β-(1,4)-linked glucose units which have a trisaccharide side chain of mannose-glucuronic acid-mannose linked to every second glucose unit in the main chain. Some terminal mannose units are pyruvylated and some of the inner mannose units are acetylated.

Heparin is a glycosaminoglycan which occurs in many mammalian tissues and has important anticoagulant and thrombolytic properties. The chemical structure is composed mainly of two disaccharide repeating units A and B. A is L-iduronic acid 2-suplhate linked α-(1,4) to 2-deoxy-2-sulfamido-D-galactose 6-sulphate while B is D-glucuronic acid β-(1,4) linked to 2-deoxy-2-sulfamido-D-glucose 6-sulphate.

Bacterial exopolysaccharide from gram negative Bacillus polymixa

Hydroxypropyl methylcellulose (HPMC or hypromellose) is a semisynthetic, inert and viscoelastic polymer that is used as eye drops and as semi-synthetic substitute for tear-films. When applied, a hypromellose solution acts to swell and absorb water, by increasing the thickness of the tear-film, resulting in decreased eye irritation.  In addition to its use in ophthalmic liquids, hypromellose has been used as an excipient in oral tablet and capsule formulations, where, depending on the grade, it functions as controlled-release agent. It is also used as a binder and as a component of tablet coatings.  Hypromellose in aqueous solution, unlike methylcellulose, exhibits thermal gelation properties. HPMC is approved as a food additive, emulsifier, thickening and suspending agent, and as an alternative to animal gelatin (Codex Alimentarius code (E number) is E464).

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.

A fucan sulphate found in brown marine algae (Phaeophyta-typically Fucus vesiculotus, Ascophyllum nodosum, Alaria and Macrocystis pyrifyra (illustrated) and has been shown to have anticoagulant activity. The main constituents are α-1,4 and α-1,2 linked L-fucose sulphates, although galactose also occurs and there are many variations of the basic structure found in different species of Phaeophyta.
The fucose content of this fucan is approx. 31% and it also contains galactose (approx. 2.2%), uronic acid (approx. 12.4%) and sulfate (approx. 32.5%).
The image was kindly provided by Prof Mike Guiry from Cork who runs ‘The Seaweed Site’.

Isolichenan is a cold-water soluble (1,3)-(1,4)-α-D-glucan isolated from lichen Cetraria islandica to have MW of about 6-8 kDa. Lichens produce isolichenan-type polysaccharides with considerable variation in linkage ratios as well as MW, even within the same species. Occasionally these α-glucans can be branched at O2, O3 or O6. The immunomodulating 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’.

Gycosaminoglycan in many organs; joint lubricant and shock absorber

Iota-Carageenan is a gelling sulphated galactan extracted from red seaweed (typically Euchuma cottonii and Euchuma spinosum). The structure of all carrageenans consists of a strictly alternating masked repeating unit of (1,3) linked α-D-galactose and (1,4) linked β-D-galactose. The α-linked galactose occurs as a 3,6-anhydro-2-sulphate unit and the β-linked sugar occurs as the 4-sulphate.
The image was kindly provided by Prof Mike Guiry from Cork who runs ‘The Seaweed Site’.

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.

Hyaluronic acid is a polysaccharide composed of repeating units of the disaccharide N-acetylglucosamine and D-glucuronic acid. It is found in many connective tissues, including the skin, where it binds water and maintains elasticity. This product is custom synthesized by modifying the structure to include fluorine atoms, methyl groups, and monosaccharides. It is synthesized from synthetic building blocks that are modified with click chemistry to form oligosaccharides. The saccharide units are then glycosylated with sugar molecules, creating a complex carbohydrate with an average molecular weight between 50,000 and 100,000 Daltons.

Curdlan is a microbial polysaccharide produced by a mutant strain of Alcaligenes faecalis var. myxogenes which was first shown to produce succinoglucan prior to mutation. Curdlan is a β-1,3 glucan forming clear solutions at about 55 °C which then gels (“low-set”) when cooled. Suspensions of curdlan at higher temperatures form firm resilient gels (“high set”) that melt at 140 - 160 °C.
The image was kindly provided by Dr. Chris Lawson.

Sugar beet arabinan consists of a 1,5 α-linked arabinose backbone to which 1,3 α-linked (and possibly some 1,2 α-linked) L-arabinofuranosyl residues are attached. Approximately 60% of the main-chain arabinofuranosyl residues are substituted by single 1,3-linked arabinofuranosyl groups. The reducing terminal arabinosyl residue is attached through rhamnose to fragments of the rhamnogalacturonan backbone of the native pectin molecule.

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.

Laminaran is a polysaccharide that co-occurs with fucoidan and alginate in brown seaweeds such as Laminaria digitata, Laminaria cloustoni, Eisenia bicyclis and Thallus laminariae. It is a β-1,3-linked glucan which it is claimed stimulates the immune system in mammals and fish.
The image was kindly provided by Prof Mike Guiry from Cork who runs ‘The Seaweed Site’.