A review of extraction methods, downstream processing, and green recovery innovations of microbial extracellular...

Extracellular polysaccharides (EPS) are structurally diverse biomolecules synthesized by a wide variety of microorganisms. Composed mainly of polysaccharides along with associated proteins and nucleic acids, EPS occur in several forms such as capsular polysaccharides attached to the cell surface, free extracellular slime, and lipopolysaccharide-associated O-antigens. These biopolymers play essential roles in microbial survival in enhancing adhesion, protecting against host immune responses, and preventing desiccation. Well-known EPS like pullulan, hyaluronic acid, and xanthan gum have found considerable industrial importance due to their biocompatibility, biodegradability, and non-toxic nature, hence encouraging their use in food, pharmaceutical, and biotechnological applications. Extraction of EPS generally involves simple steps of downstream processing like cell separation, precipitation, and drying. Though physical and chemical-based extraction methods are widely used, it is costly, environmentally cumbersome, and often provide crude extracts with residual proteins and salts. To improve recovery, pre-treatments such as dilution to reduce viscosity, heat inactivation of cells, and suppression of enzymes degrading the EPS are usually undertaken. High-purity applications may require additional deproteinization or membrane-based processes, including ultrafiltration, diafiltration, and dialysis, in spite of the challenges in membrane fouling due to the rheology of EPS. The objective of this review article is to compare the different types of extraction methods used for EPS and compare their core performance metrics, emphasizing the advantages of green innovations.