Structural features of microbial exopolysaccharides in relation to their antioxidant activity

Oxidative damage caused by free radicals is an inevitable and pervasive phenomenon that leads to cell damage and the emergence of diseases including ageing, cancer, diabetes, cardiovascular disease and neurodegenerative disorders. In this context, antioxidants play a significant role in encountering free radicals by delaying or reducing the oxidative damage of cells. Evidence suggests that synthetic antioxidants are double-edged swords wherefore the requirement for natural antioxidants is increasing globally. Exploring non-toxic, biodegradable and compatible natural molecules like exopolysaccharides can favour the current antioxidant limitations. Microbial exopolysaccharides represent a structurally diverse class of carbohydrate molecules secreted at the cell wall. Recently, bioprospecting exopolysaccharides for their astounding physiochemical properties and the reliable structure-activity relationship have motivated more research towards the investigation of their antioxidant properties. Here we propose that structural features of exopolysaccharides such as monosaccharide residues, branching, molecular weight, glycosidic linkage, functional groups, protein, selenium, and chemical modifications are likely to influence their antioxidant activity. To support this hypothesis we review the interdependence of structural features of exopolysaccharides to the observed antioxidant activity. In light of its importance, this review focuses on the understanding of the elimination of free radicals by microbial exopolysaccharides derived from marine and nonmarine sources during the last six years. [Display omitted] •Structural features such as monosaccharides, uronic acid, carboxyl, sulfate and hydroxyl groups are effectively involved in the scavenging, metal chelating and reducing activity of EPS.•EPS protects the cells against free radical accumulation and inhibits lipid peroxidation in vitro.•Chemical modifications like acetylation, carboxymethylation, sulfonation and phosphorylation enhances the antioxidant properties of EPS.•Thermostability, non-toxicity, and biocompatibility of EPS makes it preferable for wide range of biomedical applications.