Clinical-type dextran: A review on process and enzyme engineering strategies to control molecular weight distribution

Dextrans are α-(1 → 6)-linked, mostly branched α-d-glucopyranosyl polysaccharides synthesized from sucrose by lactic acid bacteria. The unique properties of dextrans, their biocompatibility, biodegradability, and non-immunogenicity support a wide range of medical and industrial applications. Key characteristics of dextran, including solubility, viscosity, and molecular weight, highly depend on the bacterial strain and the conditions under which it is synthesized. The structural diversity within the family of dextran-synthesizing enzymes contributes to dextran diversity. Conventionally, dextran with low molecular weight is obtained by fermentative production of high molecular weight dextran, followed by partial hydrolysis and a precise fractionation procedure, which is a costly and hazardous process. However, recent advances in enzyme- and bioprocess engineering in combination with analytical techniques have significantly enhanced the ability to control the molecular weight and branching patterns of dextran. Thereby improving its effectiveness and broadening its applications in both industrial and clinical settings. This review focuses on the production of dextrans with defined molecular weight and the enzymatic mechanisms underlying their synthesis, which have been increasingly studied in recent years. In particular, clinical-type dextran with a molecular weight of 70 kDa is of high commercial value and scientific interest.