Mycelial Fermentations

Two types of viscous fermentations exist (a) Mycelial fermentations viscosity is due to microbial network structure dispersed in a continuous phase, (b) Polysaccharide fermentation viscosity is due to polymer in an aqueous phase-homogeneous viscous liquid. 

An estimator (or more specifically an optimal state estimator ) in this usage is an algorithm for obtaining approximate values of process variables which cannot be directly measured. It does this by using knowledge of the system and measurement dynamics, assumed statistics of measurement noise, and initial condition information to deduce a minimum error state estimate. The basic algorithm is usually some version of the Kalman filter.14 In extremely simple terms, a stochastic process model is compared to known process measurements, the difference is minimized in a least-squares sense, and then the model values are used for unmeasurable quantities. Estimators have been tested on a variety of processes, including mycelial fermentation and fed-batch penicillin production,13 and baker s yeast fermentation.15 The... 

Moo-Young, M. Halard, B. Allen, D.G. Burrell, R. Kawase, Y. Oxygen transfer to mycelial fermentation broth in an airlift fermenter. Biotechnol. Bioeng. 1987, 30, 746-753. 

Gbewonyo K., DiMasi D., Buckland B.C., The use of hydrofoil impellers to improve oxygen transfer efficiency in viscous mycelial fermentations. Preprints of the Int. Conference on Bioreactor Fluid Dynamics, GB - Cambridge, 15.-17. 4. (1986), Paper 21... 

Some mycelial fermentations exhibit early sporulation, breakup of mycelium, and low yields if the shear is excessive. A tip speed of 250 to 500 cm/s (8 to 16 ft/s) is considered permissible. Mixing time has been proposed as a scale-up consideration, but little can be done to improve it in a large fermenter because gigantic motors would be required to get rapid mixing. Culturing cells from plants or animals is beset by mixing problems because these cell are easily damaged by shear. 

Deindoerfer (1960) and Richards (1961) have published excellent reviews on this subject, and presented an appraisal of the use of these properties in engineering and analytical correlations employed in fermentation practice. Although there are some cases where the operation and scale-up of these mycelial fermentations have been accomplished successfully using either the power input per unit volume or the overall oxygen transfer coefficient of Newtonian fluids as a basis, this does not preclude further study of the scale-up of non-Newtonian fermentation broths. On the contrary, much more information about properties such as oxygen transfer in bubble aeration, and mixing time in non-Newtonian fermentation fluids is needed to provide a better understanding of the operation and scale-up of fermentation processes. 

Intraparticle mass transfer. For some practical situations mass transfer limiting step is localized in the interior of a solid phase. This is the case for certain mycelial fermentations where the oxygen transfer via pellet or mycelial clump interior may limit growth or production processes. This situation, employing the effectiveness concept, is reviewed by Moo-Young and Blanch (lA). In the following, some other elementary phenomena and processes connected with mass transfer are reviewed. 

Nienow AW. (1990) Agitators for mycelial fermentations. Trends Biotechnol., 8 224-233. 

Moo-Young et al. [63] 760 Mycelial fermentation broths 0.07-5.3. 24-5.2 Gas holdup and volumetric mass transfer coefficients with a draft tube in the column. 

Buckland, B.C., Gwewonyo, K., DiMasi, D., Hunt, G., Westerfield, G., and Nienow, A.W. (1988) Improved performance in viscous mycelial fermentations by agitator retrofitting. BiotechnoL Bioertg., 31, TS7—H2. Heijnen, J.J. and Van t Riet, K. (1984) Mass transfer, mixing and heat transfer phenomena in low viscosity bubble column reactors. Chetn. Eng. /, 28, B21-B42. 

Gbewonyo, K., D. DiMasi, and B. C. Buckland (1987). Characterization of oxygen transfer and power absorption of hydrofoil impellers in viscous mycelial fermentations, in Biotechnology Processes, Mixing and Scale up, C. S. Ho and J. J. Ulbrecht, eds., AIChE, New York, pp. 128-134. 

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