Influence of some physicochemical factors on the viscosity of aqueous levan solutions of Zymomonas mobilis

Zymomonas mobilis strain 113 'S' produces levan - an extracellular, viscous, biologically active, non-toxic fructose polymer with a unique structure and extraordinary properties. This polysaccharide was isolated at two different degrees of purity by alcohol precipitation from aqueous solutions and was characterized with respect to some rheological properties and stability of viscous solutions. The effects of temperature, pH and salt concentration on the viscosity of 1-3% levan solutions were examined. The viscosity of levan solutions was found to be quite stable and reversible at room temperature over a wide range of pH from 4 to 11. The viscosity was slightly affected by increased salt concentration. Levan solutions were rather stable at high temperatures (up to 70°C, 1 h, pH 6), where the viscosity could be almost completely restored (up to 80-100%). Therefore, the degradation of the polymer structure under these conditions is probably insignificant. Temperatures of 70-100°C with a pH of less than 3.5 caused irreversible degradation of the levan structure. The above-mentioned properties of levan, obtained from Zymomonas mobilis 113 'S', demonstrated the potential for the development of various therapeutic forms of pharmacologically-active levan and their application in medicine as well as in the food and other industries.