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Levan is a bacterial homopolysaccharide, which consists of β-2➔6 linked β-(D)-fructose monomers. Because of its structural properties and its health promoting effects, levan is a promising functional ingredient for food, cosmetic and pharmaceutical products. The properties of levan have been reported to be linked to its molecular weight. For a better understanding of how the 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. Low molecular weight levan exhibit a compact random coil structure. As the molecular weight increases, the structure transforms into a compact non-drained sphere. The density of the sphere continues 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, can be shown for biopolymers. Our results reveal the unique properties of high-molecular weight levan and confirm the need of further systematic studies on the structure-function relationship of levan for its targeted use in food, cosmetic and pharmaceutical applications. [ABSTRACT FROM AUTHOR]

The current study investigated the molecular interactions of the exopolysaccharide levan (low and high molecular weight), β-lactoglobulin and their mixtures at different NaCl concentrations (2.5 mM and 100 mM, pH 7) using viscometry and membrane osmometry. Both methods were used to predict the phase behavior of the mixed polymer systems. A positive cross-virial coefficient indicates repulsive pair interactions between levan and β-lactoglobulin due to the excluded volume effect at both salt concentrations. A higher molecular weight of levan seemed to enhance the repulsive forces, while the NaCl concentration had only a minor influence. For the phase behavior, the charge of the β-lactoglobulin and therefore the NaCl concentration plays an important role. At low salt concentrations the repulsive, electrostatic forces between the individual β-lactoglobulin molecules counteract the concentration of the protein in one phase. Therefore, both polymers seem to be co-soluble regardless of the molecular weight of levan. At 100 mM NaCl, the electrostatic repulsion between the β-lactoglobulin molecules is screened and attractive protein - protein interactions predominated. This facilitates the formation of two phases and segregative phase separation due to the excluded volume effect becomes more likely. Image 1 • Dimerization and electrostatic interactions of β-lactoglobulin depends on NaCl. • The presence of levan promotes dimer formation of β-lactoglobulin. • Cross-virial coefficients revealed repulsive forces between levan and β-lactoglobulin. • NaCl can be used to induce or prevent segregative phase separation. [ABSTRACT FROM AUTHOR]