Question

Rheology of fermentation fluids refers to the study of

• A. Heat transfer properties
• B. Flow and deformation characteristics
• C. Oxygen transfer rates
• D. pH variations

Hint:

• Rheology: The study of how materials deform and flow under applied stress.
• Key rheological property: Viscosity.
• Newtonian fluids: Viscosity is constant (e.g., water).
• Non-Newtonian fluids: Viscosity changes with shear rate or shear stress (e.g., many fermentation broths can be shear-thinning or shear-thickening, or exhibit yield stress like Bingham plastics).
• Rheology is important in bioprocess engineering for designing and operating bioreactors and downstream processing equipment.

Answer 1

The Correct Option is B

Rheology is the branch of physics (and engineering) that deals with the deformation and flow of matter, especially non-Newtonian fluids. It studies the relationship between stress, strain, and the rate of strain. Fermentation fluids (broths) can exhibit complex rheological behavior, especially at high cell densities or when microorganisms produce viscous exopolysaccharides or form filamentous structures (like some fungi or actinomycetes). The rheological properties (e.g., viscosity, shear stress vs. shear rate relationship) of the fermentation fluid are crucial because they affect:

• Mixing efficiency and power consumption for agitation.
• Mass transfer rates (e.g., oxygen transfer, nutrient distribution).
• Heat transfer rates.
• Pumping and processing of the fluid.

Therefore, rheology of fermentation fluids refers to the study of their flow and deformation characteristics. Let's analyze the options: (a) Heat transfer properties: Affected by rheology, but rheology itself is not the study of heat transfer. (b) "Flow and deformation characteristics": This is the direct definition of rheology. (c) Oxygen transfer rates: Affected by rheology, but rheology is not solely the study of OTR. (d) pH variations: pH is a chemical property, not directly rheology. Thus, option (b) is the correct definition. \[ \boxed{\text{Flow and deformation characteristics}} \]