Levan Polymers: Biosynthesis, Structural Diversity, and Functional Applications

Levan is a structurally diverse β-(2 → 6)-linked fructan biopolymer with occasional β-(2 → 1) branching and a terminal α-d-glucopyranose residue, synthesized by plants, bacteria, fungi, and archaea through the catalytic action of levansucrases. Its molecular weight ranges from a few thousand to several million Daltons, depending on the enzymatic system and synthesis conditions. This review provides an integrative analysis of levan biosynthesis, structural diversity, and the factors controlling molecular weight distribution, degree of branching, and polymer architecture. Advances in chromatographic and spectroscopic methodologies improve structural resolution, enabling a deeper understanding of structure-function relationships and facilitating the rational design of levans with defined physicochemical and biological properties. In addition to polymer formation, levansucrases catalyze transfructosylation reactions toward a wide variety of acceptor molecules, leading to the synthesis of functional fructosides, sucrose analogs, and fructooligosaccharides with potential industrial and biomedical applications. Overall, levan emerges as a renewable and multifunctional macromolecule whose tunable structural features underpin its growing relevance in food, pharmaceutical, and materials science applications, while key challenges remain in achieving controlled biosynthesis and large-scale production.