Question

Select the correct statement/s regarding the action of rennet from the following:
(A). Breaking of protective colloids of casein and release of non protein nitrogen
(B). Removal of the colloidal calcium phosphate from casein
(C). Over all hydrolysis of all casein components under the protective action of casein
(D). Formation of casein coagulum
Choose the correct answer from the options given below:

• A. (A), (B) and (D) only
• B. (A), (C) and (D) only
• C. (A), (B), (C) and (D)
• D. (B), (C) and (D) only

Hint:

Remember that the primary action of rennet is highly specific:
- It targets only the \(\kappa\)-casein fraction on the micelle surface, breaking the protective colloid and forming the coagulum without causing general proteolysis of other caseins.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Rennet acts on milk to form a curd by altering the colloidal stability of casein micelles.
This process involves specific enzymatic cleavage followed by a structural rearrangement of the micelles.

Step 2: Detailed Explanation:
Let us evaluate each statement regarding the action of rennet:
-(A) Breaking of protective colloids of casein and release of non-protein nitrogen:
This statement is correct.
Casein micelles are stabilized in solution by a surface "hairy" layer of \(\kappa\)-casein, which acts as a protective colloid.
Rennet specifically cleaves \(\kappa\)-casein at the \(\text{Phe}_{105}-\text{Met}_{106}\) bond, releasing the hydrophilic glycomacropeptide (GMP) into the whey.
Since GMP remains soluble and is not precipitated with the curd, it behaves as non-protein nitrogen (NPN) in subsequent whey analysis.
This cleavage removes the protective steric barrier of the micelles.
-(B) Removal of the colloidal calcium phosphate (CCP) from casein:
This statement is correct in the context of the colloidal structure modification.
During coagulation, the structural changes and localized calcium interactions alter the association of CCP within the micelle core, facilitating the transition from a stable micelle to an aggregating network.
-(D) Formation of casein coagulum:
This statement is correct.
Once the protective barrier is removed and calcium bridges form, the para-casein micelles aggregate to form a continuous three-dimensional network, or casein coagulum.
-(C) Over all hydrolysis of all casein components...
This statement is incorrect.
Rennet is highly specific and does not cause general hydrolysis of all casein fractions during coagulation; general proteolysis only occurs slowly over months during cheese ripening.
Therefore, statements (A), (B), and (D) are correct.

Step 3: Final Answer:
The correct statement combination is (A), (B), and (D) only, which corresponds to Option (A).