POLYSACCHARIDES FROM CYANOBACTERIA .4. RHEOLOGY OF CULTURE BROTHS AND EXOPOLYSACCHARIDE OF CYANOSPIRA-CAPSULATA AT DIFFERENT STAGES OF GROWTH

This study deals with the rheological behaviour of the culture broths of the exocellular polysaccharide producer cyanobacterium Cyanospira capsulata at different culture times. The non-Newtonian character of the culture broths is mainly due to the presence of the exopolysaccharide solubilized into the medium but the contribution of the microbial cells cannot be considered to be negligible. particularly at the early stages of the microbial growth. The culture broths exhibit shear-thinning behaviour and the Carreau viscosity equation appears to fit the experimental data fairly well. The culture broths show elastic behaviour as well. Non-linear viscoelastic behaviour has also been investigated. The shear viscosity curve as well as oscillatory flow tests of the old culture (28 days after the inoculum) show some 'anomalies' which can be ascribed to a decrease in the exocellular polysaccharide molecular weight.