Polysaccharides

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.

Nigeran is a polysaccharide found in the cell wall of lower fungi. In certain Aspergillus and Penicillium spp., nigeran was first isolated from Penicillium expansum and Aspergillus niger (illustrated). The polysaccharide contains unbranched α-D- glucopyranose residues linked 1,3 and 1,4. Nigeran is part of the hyphal cell wall, where it can contribute up to 40 % of the cell dry weight. The polysaccharide occupies several domains or location on the hyphal wall and is highly crystalline in vivo. Deposition of nigeran is primarily at the outer surface of the hyphal wall.

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.

Guar gum is obtained from the seed of the legume Cyamopsis tetragonolobus, an annual plant that grows mainly in semi-arid regions of India. The structure of the polysaccharide consists of a main chain of (1,4)-linked β-D-mannopyranosyl units with single α-D-galactopyranosyl units linked (1,6) on average to every second main chain unit. Guar has a high viscosity in aqueous solution, shows marked pseudoplastic behaviour and forms synergistic gels in the presence of other gums such as carrageenan and xanthan gum.

Propylene glycol alginate is a reaction product of propylene oxide and alginic acid. At the 49th JECFA meeting (1997) it was resolved that the total dietary propylene glycol intake from all sources should be allocated an ADI of 0-25 mg/kg.  Applications include as a stabiliser in beer foam due to electrostatic interaction between carboxyl groups on the glycol alginate molecules and amino groups on the peptides in the bubble wall and in ice cream by emulsifying the fat.Esterification is greater then 80%Viscosity (1% aq solution): 200-300 mpa.s

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’.

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.