Using a flexible shaft agitator to enhance the rheology of a complex fungal fermentation culture

Abstract

The rheology behavior of biological fluids particularly when the viscosity is high and rheology is complex, is an important issue to understand, particularly for studies in mass-transfer and for solving technical problems with mixing in stirred bioreactors. In this paper, the use of a Swingstir(®) impeller during the fermentation of Aspergillus oryzae resulted in decreases from the parameters of a power-law model, in viscosity and in the thixotropic behavior of a cultivation broth. The results showed that both the K L a and the alpha amylase activity were improved when using the Swingstir(®) in comparison with Fullzone(®) impeller (FZ) at the same level of energy consumption. Increasing the pellet porosity during mixing via the Swingstir(®) resulted in increases in oxygen mass transfer and the average shear stress.

Effect of Macroporous Support Particles on Cell Immobilization, Mass Transfer and Rheology in a Stirred Cultivation of Aspergillus oryzae Using a Swingstir® Mixer

“…Without the use of support particles, however, K was increased, from the first sampling to the end of the fermentation. Previous studies have shown that increasing the broth viscosity makes cultivation a challenge [13], [17]. These results show that utilizing large BSPs could be an easy solution to decreasing the non-Newtonian properties and preventing the obstacles that arise from a high-viscosity cell culture.…”

“…In the culture containing small particles, the main reason for the loss of the immobilized cells was the structure of the particles. According to previous publications, [13] the average pellet size of the small-particle cells at 72 h was approximately 6.5 mm and the small pellets could not stably adhere with such a small surface area (3*6 or 3*3 ). The decrease in the culture when using 1,000large BSPs was obviously neither the number of particles nor the structure, which suggests more study on morphology is needed in the near future to determine the reason.…”

“…In previous reports, increasing the broth viscosity and strong shear-thinning behavior of fermented fluid was presented a challenge for fungal cultivation [13], [17]. Experimental studies show the power-law model for fermentation fluid even under immobilization conditions.…”

“…Agitation was provided via a Swingstir ® . In a previous study, [13] the Swingstir ® was described as a flexible agitator that would be convenient for the submerged fermentation of A. oryzae. The positive hydrodynamic behavior of the Swingstir ® was a direct result of its use of un-steady vortices [13].…”

Multiphase Stirred Tank Bioreactors – New Geometrical Concepts and Scale‐up Approaches

“…Besides the attempt to avoid, e.g., high values of shear stress responsible for the disintegration of microorganisms, by geometrical adjustments of the impeller, one approach considering the potentially changing rheological behavior of the cultivation broth during the fermentation time is using flexible parts in the stirring system. Ghobadi et al , applied the Swingstir® impeller (SS) in their fungus cultivation experiments and compared its performance with a Fullzone® impeller (FZ; large impeller covering the whole filling height just at the lower limit of the near‐wall d / D value) and two 6‐SBDTs in a multistage arrangement. The SS is an off‐center stirrer with a flexible shaft moving concentrically above the aerator.…”