INFLUENCE OF SOME PHYSICOCHEMICAL FACTORS ON THE VISCOSITY OF AQUEOUSLEVAN 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 isola ted at two different degrees of purity by alcohol precipitation from a queous solutions and was characterized with respect to some rheologica l properties and stability of viscous solutions. The effects of temper ature, pH and salt concentration on the viscosity of 1-3% levan soluti ons were examined. The viscosity of levan solutions was found to be qu ite stable and reversible at room temperature over a wide range of pH from 4 to 11. The viscosity was slightly affected by increased salt co ncentration. Levan solutions were rather stable at high temperatures ( up to 70 degrees C, 1 h, pH 6), where the viscosity could be almost co mpletely restored (up to 80-100%). Therefore, the degradation of the p olymer structure under these conditions is probably insignificant. Tem peratures of 70-100 degrees C with a pH of less than 3.5 caused irreve rsible degradation of the levan structure.The above-mentioned properti es of levan, obtained from Zymomonas mobilis 113 ''S'', demonstrated t he potential for the development of various therapeutic forms of pharm acologically-active levan and their application in medicine as well as in the food and other industries.