(70c) Rheological Properties of a Suspension of Disintegrated Yeast Cells

The knowledge of rheological parameters of microorganism suspensions is necessary for an optimal management of a number of industrial bioprocesses. They include, among the others, the disintegration of microbial cells. Disruption of microorganisms, release of intracellular compounds, microgrinding of cell fragments and cutting of high-molecular compounds that occur in these processes, may induce continuous changes of rheological properties. Studies of rheological properties were performed in a suspension of baker's yeast Saccharomyces cerevisiae. Concentration of the suspension was changed. Measurements were made using cylindrical rotary rheometers RC20 and CVO120 and a double gap cylindrical rotary rheometer RC20. Flow curves were determined at the temperature 4°C for the suspension of yeast cells disintegrated at different levels and its supernatant. A standard liquid was triethylene glycol. The yeast cells were disintegrated in a bead mill. Changes in rheological properties of the suspension were described mathematically depending on the solution concentration and the level of cell disintegration. A suspension of microorganisms behaves like a Newtonian liquid. An increase of cell concentration causes that apparent viscosity increases. Destruction of spatial structures of cells in the suspension at high concentrations induces an abrupt decrease of apparent viscosity. An opposite effect causes a release of intracellular compounds.