Question

Given below are two statements:
Statement (I): Rennet activity can be measured by viscosity change and visual precipitation.
Statement (II): The optimal pH for rennet activity is 5.3 to 5.5 and it is a first order reaction.
In light of the above statements, choose the most appropriate answer from the options given below.

• A. Both Statement (I) and Statement (II) are correct
• B. Both Statement (I) and Statement (II) are incorrect
• C. Statement (I) is correct but Statement (II) is incorrect
• D. Statement (I) is incorrect but Statement (II) is correct

Hint:

Remember the two distinct phases of rennet action:
1. Primary enzymatic phase \(\rightarrow\) Hydrolysis of \(\kappa\)-casein, follows first-order kinetics, optimal at acidic pH (5.3 - 5.5).
2. Secondary aggregation phase \(\rightarrow\) Non-enzymatic, temperature-dependent, requires calcium ions.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Rennet is a complex of enzymes, primarily chymosin, used in cheese manufacture to coagulate milk.
The coagulation process involves an enzymatic primary phase (hydrolysis of \(\kappa\)-casein) followed by a non-enzymatic secondary phase (calcium-mediated aggregation of micelles).

Step 2: Detailed Explanation:
Let us evaluate both statements:
-Statement (I): "Rennet activity can be measured by viscosity change and visual precipitation."
This statement is correct.
As rennet acts on milk, the primary phase reduces the steric stability of the casein micelles, allowing them to aggregate and form a gel network.
This gelation process causes a measurable increase in the viscosity of the milk.
Viscometric methods track this change to determine clotting kinetics.
Alternatively, standard methods like Berridge's clotting time test rely on visual observation of the first appearance of discrete protein flakes or precipitation on the walls of a rotating tube.
-Statement (II): "The optimal pH for rennet activity is 5.3 to 5.5 and it is a first order reaction."
This statement is correct.
The primary enzymatic phase of rennet coagulation involves the specific cleavage of the \(\text{Phe}_{105}-\text{Met}_{106}\) bond of \(\kappa\)-casein.
The catalytic efficiency of chymosin on this bond increases as the pH is lowered from the natural pH of milk (6.7) toward acidic levels, with an optimum operating pH in milk systems between 5.3 and 5.5.
Furthermore, under standard assay conditions where the substrate (\(\kappa\)-casein) concentration is low relative to the Michaelis constant, this enzymatic hydrolysis reaction follows first-order reaction kinetics.
Therefore, both Statement (I) and Statement (II) are correct.

Step 3: Final Answer:
Both Statement (I) and Statement (II) are correct, which corresponds to Option (A).