The morphology of filamentous microorganisms does essentially affect the production of metabolites. Agitating conditions may affect the morphology and for this reason the production of metabolites too.The following parameters it was found to have an influence:
Reynolds mixing number
impeller blade tips velocity
mean shear stress close to the impeller
impeller power consumption per unit volume
cavitation pressure drop
It were presumed three mechanisms for the mechanical effect on the microorganisms:
the direct impact of the impeller blades on the microorganisms‐collision
the shear stress in the liquid phase
a sharp pressure decrease behind the impeller blades‐cavitation
Mathematical relationships are developed for the different mechanisms.Using Aspergillus niger it is shown what morphological and physiological states of this microorganism are caused by mechanical straining and the conditions for the maximal production of citric acid are studied.Requirements for scale‐up are discussed.
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