Question

A concentrated solution of the limiting substrate is added in fed-batch at a rate?

(a) Greater than the solution of the limiting substrate and the same medium used to establish the batch culture

(b) Less than the solution of the limiting substrate and the same medium used to establish the batch culture

(c) Equal to the solution of the limiting substrate and to the same medium used to establish the batch culture

(d) Negligible to the solution of the limiting substrate and to the same medium used to establish the batch culture

I have been asked this question in examination.

Query is from Fed Batch Culture topic in chapter Microbial Growth Kinetics of Bioprocess Engineering

Answer 1

The correct answer is:

(b) Less than the solution of the limiting substrate and the same medium used to establish the batch culture

Explanation:

In fed-batch culture, a concentrated solution of the limiting substrate is added at a controlled rate to maintain an optimal concentration of the limiting nutrient. The goal is to avoid excessive accumulation of the substrate, which could lead to inhibitory effects or byproduct formation, and to ensure that the growth rate is maintained at an optimal level for the microorganisms.

• (a) Greater than the solution of the limiting substrate and the same medium used to establish the batch culture: Adding substrate too rapidly or in excess would lead to a high concentration of the limiting substrate, which is not ideal as it could cause substrate inhibition or lead to excess biomass growth.

• (b) Less than the solution of the limiting substrate and the same medium used to establish the batch culture: This is the correct approach in fed-batch culture. The addition rate is less than the rate at which the microorganism consumes the substrate, ensuring that the substrate is consumed at a controlled rate without overfeeding.

• (c) Equal to the solution of the limiting substrate and to the same medium used to establish the batch culture: This is typically not ideal, as it may lead to excessive accumulation of the limiting substrate, causing issues like inhibition or overfeeding.

• (d) Negligible to the solution of the limiting substrate and to the same medium used to establish the batch culture: This would mean that no fed-batch feeding is occurring, and it would not help maintain the desired growth conditions. Therefore, this option is incorrect.

In summary, in fed-batch culture, you add the limiting substrate at a slower rate than its consumption rate to maintain continuous and controlled growth.