Gellan gum is a microbial exopolysaccharide that is commercially useful as a culture media additive, a food additive according to the US regulation of FDA 21 CFR 172.665) and for the encapsulation of drugs (Prajapati et al., 2013). The main functional benefits are as a gel and stabiliser in both food, consumer healthcare and pharmaceutical industries. It is one of the most expensive gums at the moment.
The gum is non-toxic and there are few safety considerations in its handling or use (Anderson et al., 1988).
Gellan gum is produced by Sphingomonas elodea (ATCC 31461), (ex. Pseudomonas elodea) or Auromonas elodea (Pollock, 1993).
Its native form is composed of a repeating unit of monomers, tetrasaccharide, that are made up of two residues of D-glucose and one each of the sugars D-glucuronic acid and L-rhamnose. The repeating unit is:
[→3)-β-D-Glcp-(1→4)-β-D-GlcAp-(1→4)-β-D-Glcp-(1→4)-α-l-Rhap-(1→] with esters at C-2 and C-6 of the 1,3-D-glucose residue. These esterification modifications consist of glycerate at C-2 and acetate with the acetylation of 50% of the residues (Kuo et al., 1986).
Gellan gum is widely used as a gelling agent and stabilizer in the food industry. HA gellan gum gives soft, elastic and transparent gels at concentrations higher than 0.2%. HA gels set and melt at 70 to 80 °C with no thermal hysteresis. However, LA gellan gum can form hard, non-elastic and brittle gels in the presence of cations; the gel strength of LA gellan gum increases with increasing ion concentration. The LA gellan gels also exhibit significant thermal hysteresis.
Research on various complexes of Ge with polymers, such as chitosan, konjac glucomannan, and k-carrageenan, have been reported with intermolecular hydrogen bonds between the gums. This results in good elasticity and excellent breaking strength in the films (Lee et al., 2004).
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