Engineering Advances in Fermentation Practice Rheological Properties of Fermentation Broths rheological properties offermentation broths markedly influence the nature of the fluid regime in aerated and agitated fermentors and, as a consequence, are important factors in the consideration of mass, heat, and momentum transfer during a fermentation. Rheological properties usually change appreciably during this time and these changes must be taken into account in any logical unit operational study or correlation. In an analytical capacity, these changes also provide information about the growth of the microorganism. Available evidence ( 4 ) indicates that fermentation broths containing unicellular microorganisms of simple shape should behave as Newtonian fluids, and their viscosity is predictable by equations used in colloid chemistry to relate suspension viscosity with particle volume. In many industrial fermentations, however, the broths are too complex to be described adequately by a single property such as viscosity-especially in fermentations employing filamentous microorganisms such as molds and actinomycetes, where deviations from Newtonian behavior are appreciable. Although the literature describing the behavior of non-Newtonian fluids is extensive (6),reported analyses of fermentation broths in the light of such behavior are few. A number of industrially important fermentation broths appear to fit the behavior patterns of the flow models shown in the figure. The table summarizes the nature and rheological character of these broths. In several instances the broths exhibited two types of behavior, depending upon their stage of development during the course of the fermentation. T H E
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Several important flow models f r e quently used in characterizing fluids
dv/dy Despite evidence of frequent nonNewtonian behavior, most published design and scale-up procedures used in fermentation engineering fail to take this into account. There is a need for development of more suitable correlations for these purposes. Because rheological properties provide a sensitive analytical means for characterizing mass cellular changes, studies along these lines may furnish a clue to the relationship between cellular structure and biochemical activity in a fermentation. The rheology of fermentation broths, therefore, appears promising for future studies.
47th Meeting, Am. Inst. Chem. Engrs. New York, N. Y., December 1954. (2) Deindoerfer, F. H., Gaden, E. L., Jr., Appl. Microbiol. 3,253 (1955). (3) Deindoerfer, F. H., West, J. M., J. Microbiol. Biochem. Technol. Eng.,
in Dress.
(4) &rich, F., Bunzl, M., Margaretha, H., Kolloid Z. 74, 276 (1936). (5) Karow, E. O., Bartholomew, W H., Sfat, M. R., J . Agr. Food Chem. 1, 302 (1953). (G) Metzner. A. B.. “Advances in Chemi’ cal Engineering;” vol. I, Chap. 2, Academic Press, New York, 1956.
FRED H. DEINDOERFER‘ JOHN M. WEST Squibb Institute for Medical Research, New Brunswick, N. J.
literature Cited (1) Brown, G. A., Petsiavas, D. N.,
Biochemical Engineering Symposium,
Rheological Character of Several Fermentation Broths Principal Medium Rheological Ingredients Behavior Process Microorganism Nystatin Streptomyces noursei Soybean meal, glu- Newtonian cose Penicillin Penicillium chryso- Corn steep liquor, Pseudoplastic genum lactose Plastic Steroid hydroxylation Coniothyrium helEe- Salts, glucose Plastic and bori pseudoplastic Streptomycin Streptomyces griseus Soybean meal, glu- Newtonian and cose plastic Plastic Unidentified Unidentified mold Unidentified Plastic
Velocity gradient
Present address, School of Chemical Engineering, University of Pennsylvania, Philadelphia 4, Pa.
The complete papers presented in the Symposium on Engineering Advances in Fermentation Practice before the Division of Agricultural and Food Chemistry at the 136th Meeting of the American Chemical Society, Atlantic City, N. J., September 1959, will be published in the January 1960 issue of Advances in Applied Microbiology (Vol. II), Academic Press, New York, N. Y.
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