Question

Which one of the following represents non-growth associated product formation kinetics in a bioprocess system? $X$ and $P$ denote viable cell and product concentrations, respectively. 

• A. A
• B. B
• C. C
• D. D

Hint:

If the product curve rises only after biomass stops growing, it is a non-growth associated (secondary metabolite) process.

Answer 1

The Correct Option is C

In bioprocess kinetics, product formation can occur through two major mechanisms: growth-associated and non-growth-associated. Understanding the difference is essential to identify the correct plot.

Step 1: Growth-associated product formation.
In growth-associated kinetics, product formation occurs simultaneously with biomass growth. Hence, \(P\) increases in proportion to \(X\). Their curves follow similar trends and both reach stationary phase together. This matches options (A) and partially (B).

Step 2: Non-growth associated product formation.
In non-growth associated kinetics, the product is synthesized only after the cells reach the stationary phase. Biomass concentration \(X\) remains constant, but product concentration \(P\) continues to increase. This behavior is typical for secondary metabolites such as antibiotics, pigments, and certain organic acids.

Step 3: Analyze the given plots.
- In (A), both \(X\) and \(P\) level off together → growth associated.
- In (B), product formation follows growth, but not clearly separated → partially growth-associated.
- In (C), \(X\) reaches a plateau (stationary phase) but \(P\) begins to increase linearly afterward. This is the signature of non-growth associated product formation.
- In (D), product decreases as biomass increases → biologically incorrect for typical product pathways.

Step 4: Conclusion.
Option (C) correctly represents non-growth associated kinetics because product formation continues even after cell growth ceases.