Question

Given below are two statements, one is labelled as Assertion (A) and other one labelled as Reason (R).
Assertion (A) : The redox potential (Eh) of cheese and fermented milk products is more negative than that of milk.
Reason (R) : A rapid decrease in Eh occurs after the available oxygen has been consumed by the bacteria.
In light of the above statements, choose the correct answer from the options given below.

• A. Both (A) and (R) are true and (R) is the correct explanation of (A).
• B. Both (A) and (R) are true but (R) is NOT the correct explanation of (A).
• C. (A) is true but (R) is false.
• D. (A) is false but (R) is true.

Hint:

Dissolved oxygen is a strong oxidizing agent that keeps \( E_h \) positive.
Bacterial growth consumes this oxygen, creating reducing conditions and shifting the \( E_h \) to negative values.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
The redox potential (\( E_h \)) of a dairy product represents its oxidation-reduction state.
Fresh, aerated milk has a positive redox potential (typically \( +150\text{ mV} \) to \( +250\text{ mV} \)) due to the presence of dissolved oxygen.
During fermentation, microbial metabolism significantly alters this parameter.

Step 2: Detailed Explanation:
Let us evaluate the Assertion and the Reason:
- Assertion (A): In cheese and fermented milk products (like dahi or yogurt), the redox potential is highly negative (ranging from \( -100\text{ mV} \) to \( -250\text{ mV} \)), making it much more negative than fresh milk.
Thus, Assertion (A) is true.
- Reason (R): Lactic acid bacteria grow rapidly during fermentation, utilizing the dissolved oxygen as an electron acceptor or consuming it through respiration/metabolism.
Once the available dissolved oxygen is depleted, the environment becomes anaerobic/reducing, causing a sharp, rapid decrease in the \( E_h \) value to negative levels.
This biological oxygen consumption is the direct cause of the negative redox state in fermented products.
Thus, Reason (R) is true and directly explains Assertion (A).
Therefore, both statements are true and (R) is the correct explanation of (A).

Step 3: Final Answer:
Both (A) and (R) are true and (R) is the correct explanation of (A), corresponding to option 1.