  Levan is a bacterial homopolysaccharide, which consists of beta-2,6 linked
beta-D-fructose monomers. Because of its structural properties and its health
promoting effects, levan is a promising functional ingredient for the food,
cosmetic and pharma industry. The properties of levan have been reported to be
linked to its molecular weight. For a better understanding of how its molecular
weight determines its polymer conformation in aqueous solution, levan produced
by the food grade acetic acid bacterium Gluconobacter albidus TMW 2.1191 was
analysed over a broad molecular weight range using dynamic and static light
scattering and viscometry. Levan, with low molecular weight, exhibited a
compact random coil structure. As the molecular weight increased, the structure
transformed into a compact non-drained sphere. The density of the sphere
continued to increase with increasing molecular weight. This resulted in a
negative exponent in the Mark-Houwink-Sakurada Plot. For the first time, an
increase in molecular density with increasing molecular weight, as determined
by a negative Mark-Houwink-Sakurada exponent, could be shown for biopolymers.
Our results reveal the unique properties of high-molecular weight levan and
indicate the need of further systematic studies on the structure-function
relationship of levans for their targeted use in food, cosmetic and
pharmaceutical applications.
