Crossflow Microfiltration

Owing to parallel investigations using different crossflow systems (17), it is strongly recommended that the application of PROSTAK™ flat membrane (0.1 |m) modules (see Subheading 2.4.) operating in crossflow mode for the purification (diafiltration mode) and concentration (Fig. 5) of the cell-free Schizophyllan solution.

Connect three filtration modules in series each with a area of 0.17 m2. The tangential feed velocity of the retentate varies between 1 and 6.6 m/s. Best results related to a high permeation rate are achieved when the tangential feed velocity is at its individual maximum avoiding a transmembrane pressure >0.8 bar (see Note —). This optimum adjustment can be easily attained in the purification step using the diafiltration mode (Fig. 5). In this context, purification means that the Schizophyllan molecules are fully rejected and low molecular compounds (<0.1 |m), such as proteins, glucose, and salts, permeate

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Schematic setup of the crossflow microfiltration for the purification (diafiltration) and concentration of cell-free Schizophyllan solutions (V = volume feed; L/h).

Schematic setup of the crossflow microfiltration for the purification (diafiltration) and concentration of cell-free Schizophyllan solutions (V = volume feed; L/h).

through the membrane. Let the output permeate flow equal the input solvent (water) flow, so that the volume of the retentate remains constant. This procedure enables only a small decrease of the permeation rate, leveling off at approx 30 L/h • m2. The grade of purification depends on the application of the Schizophyllan and has to determined individually (e.g., protein content).

Stop the input of water flow after sufficient purification of the Schizophyllan solution and

concentrate the solution subsequently to a final content of 10 g/L at maximum (see Note ). During this process, the negative influence of fouling at the membrane surface is increased with the consequence of a continual decrease in the permeation rate (Fig. 6). A highly viscous, colorless, eo

Schizophyllan (g/I) Fig. 6.

Decrease of the permeation rate during the concentration run of a cell-free Schizophyllan solution applying crossflow microfiltration.

Schizophyllan (g/I) Fig. 6.

Decrease of the permeation rate during the concentration run of a cell-free Schizophyllan solution applying crossflow microfiltration.

and transparent solution is the result of this procedure. Drying or lyophilization of the product solution has to be avoided, because only 50% (w/w) of the dried Schizophyllan is resoluble in water. Otherwise dimethylsulfoxide dissolves the dried Schizophyllan to 100%. However, this solvent degrades the triple helix to single-coiled chains with drastic reduction of viscosity.

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