Welan gum is a high-molecular-weight microbial exopolysaccharide produced by Alcaligenes (now classified within the genus Sphingomonas) species through aerobic fermentation. It is valued for its exceptional rheological stability under harsh environmental conditions.
Molecular Structure
Welan gum consists of a linear tetrasaccharide repeating unit →4)-β-D-Glcp-(1→4)-β-D-GlcpA-(1→4)-β-D-Glcp-(1→4)-α-L-Rhap-(1→, with a single side chain of either α-L-rhamnopyranosyl or α-L-mannopyranosyl residues (in an approximate 2:1 ratio) attached at the C-3 position of the fourth glucose unit. In addition, O-acetyl groups are present at an average frequency of one per repeating unit. The resulting polymer exhibits a molecular weight in the range of approximately 1–10 × 106 Da and adopts a three-fold double-helical conformation in solution, stabilized by extensive hydrogen bonding. Compared with gellan gum, welan gum displays greater chain rigidity, attributed to steric shielding of carboxylate groups by its side chains.
Production and Properties
Welan gum is produced by fermentation of glucose or molasses using Alcaligenes sp. ATCC 31555 at approximately 30 °C and pH 6.5–7.0 under conditions of high aeration, followed by recovery through alcohol precipitation to yield a cream-colored powder. Owing to its glucuronic acid content, the polymer behaves as an anionic polyelectrolyte and exhibits pronounced shear-thinning viscosity, yield stress, thixotropy, and viscoelastic behavior. These properties are superior to those of xanthan gum in high-salinity media such as brines and seawater. Aqueous solutions remain stable at temperatures up to 120 °C, across a broad pH range (2–12), and in sodium chloride concentrations of up to 20%. Variants enriched in mannose side chains display higher storage and loss moduli.
Biomedical Applications
The favorable biocompatibility of welan gum supports its use in hydrogel formulations for controlled drug delivery systems and in scaffold materials for tissue engineering. Its low immunogenicity further enables application as a pharmaceutical viscosity-modifying excipient. However, the limited availability of clinical data currently constrains broader therapeutic implementation.