Sulfated Polysaccharides from Brackish and Fresh Water Red Microalgae: Rheological and Structural Characteristics

A comparative study of the sulfated polysaccharides produced by two species of red microalgae the brackish water Dixoniella grisea and the freshwater Porphyridium aerugineum – was conducted with the aim to unravel their structure/function relationships. To this end, the similarities and differences in composition, physical properties and biocompatibilities were investigated. Both polysaccharides were found to be composed of 6-8 monosaccharides the main being xylose, sulfur content was found to be 1-1.7%. Both species exhibited shear thinning and weak gel behavior and both were highly viscous at relatively low polymer concentrations. The two polysaccharides were found to be stable in alkaline environment, whereas, in acidic environment an opposite trend was observed: while the viscosity of the polysaccharide of the brackish water increased, that of the fresh water decreased. The polysaccharides of the two species showed similar morphology, having a porous fibrous structure with a rough amorphous surface. The cytotoxicity evaluation (in vitro) using 3T3 fibroblast showed that both species are biocompatible at low polysaccharide concentrations (≤0.05% w/v) while at higher concentration (0.1% w/v) the viability of the cells decreased probably as a result of impaired nutrient transfer.

Studying these polysaccharides will be valuable for the development of innovative applications and products for the biotech industries e.g. food additives, thickeners and drug delivery agents.