Gellan gum is a microbial exopolysaccharide produced by Sphingomonas elodea (formerly Pseudomonas elodea). It is widely valued for its versatile gelling and stabilizing properties in food, pharmaceutical, and biomedical applications.
Molecular Structure
Gellan gum consists of a linear tetrasaccharide repeating unit with the structure: →3)-β-D-Glc-(1→4)-β-D-GlcA-(1→4)-β-D-Glc-(1→4)-α-L-Rha-(1→. The monosaccharide composition follows a 2:1:1 ratio of glucose, glucuronic acid, and rhamnose.
Native high-acyl gellan contains acetate (one per disaccharide) and glycerate (one per tetrasaccharide) substituents attached to the first glucose residue. In contrast, low-acyl gellan lacks these substituents, resulting in molecular weights typically ranging from 500 to 2000 kDa. The polymer adopts a double-helix conformation that is stabilized by the presence of cations.
Production and Properties
Gellan gum is produced through aerobic fermentation using glucose or starch hydrolysates as carbon sources, typically at 30°C and pH 6–7. Following fermentation, alkali treatment is applied to obtain low-acyl gellan, after which the polymer is recovered by alcohol precipitation and drying.
Gellan gum exhibits high thermal stability and broad pH tolerance (approximately pH 3.5–10). It is water-soluble above 40°C, while high-acyl gellan can hydrate in cold water in the presence of sequestrants. The polymer displays shear-thinning rheological behavior and undergoes cation-induced gelation: high-acyl gellan forms soft and elastic gels in the presence of monovalent cations (K⁺, Na⁺), whereas low-acyl gellan forms firm and brittle gels when exposed to divalent cations (Ca²⁺, Mg²⁺). Gellan gum is biodegradable and holds GRAS (Generally Recognized As Safe) status.
Biomedical and Pharmaceutical Applications
In biomedical and pharmaceutical fields, gellan gum is used to form injectable hydrogels for drug delivery and tissue engineering applications, benefiting from its biocompatibility, ability to encapsulate cells, and capacity for controlled release. It is also employed in vegetarian capsule shells as a replacement for gelatin.
Additionally, gellan gum supports ophthalmic formulations and wound dressing materials due to its optical transparency, mechanical brittleness, and excellent moisture retention properties, making it a valuable polysaccharide for advanced therapeutic applications.
