levans

Levans are a family of high-molecular-weight exopolysaccharides composed predominantly of fructose units. They are fructans produced by a variety of microorganisms and, in some cases, plants. The term levans is used to describe levan-type polymers produced by different sources, which can differ in molecular weight, branching, and exact linkage patterns.

Biosynthesis is catalyzed by levansucrase, an enzyme that polymerizes fructose from sucrose while releasing glucose. The polymers may be secreted into the culture medium or remain attached to the cell surface. Molecular weights commonly range from around 10^5 to 10^6 Daltons or higher, and production conditions influence size and branching.

Structurally, levans are primarily beta-D-fructofuranose chains linked mainly by beta-2,6 bonds, with occasional beta-2,1 branches in some variants. They are typically water-soluble and nonionic, forming viscous solutions that can function as thickening or stabilizing agents. The properties depend on source and processing.

Levans are produced industrially by fermentation using levansucrase-active microbes such as certain Bacillus, Zymomonas, and Erwinia species. Purified levans find use as ingredients in foods and cosmetics and as research materials. In biomedical contexts they are studied as prebiotics, drug delivery matrices, and biocompatible scaffolds. Safety and regulatory status depend on source and purity.

Levans share features with other fructans, such as inulin.