Question

The rennet coagulation of casein during cheese making is prolonged or prevented when the temperature of milk is maintained above __________.

• A. 60 °C
• B. 70 °C
• C. 50 °C
• D. 40 °C

Hint:

Rennet enzymes (primarily chymosin) are extremely heat-sensitive.
They exhibit an optimum temperature of \(40\text{-}42^\circ\text{C}\) and undergo rapid thermal inactivation above \(50^\circ\text{C}\).

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Rennet coagulation of milk is a two-stage biochemical process consisting of an enzymatic phase and a subsequent non-enzymatic physical aggregation phase.
Both stages are highly sensitive to temperature, as the primary enzyme in rennet (chymosin) is a protein subject to thermal denaturation.

Step 2: Detailed Explanation:
The coagulation of casein micelles by rennet requires an optimal temperature range of \(40^\circ\text{C}\) to \(42^\circ\text{C}\) for maximum enzymatic activity and hydrophobic aggregation.
When the temperature of the milk is lowered below \(15^\circ\text{C}\), the secondary physical aggregation phase ceases completely, although the enzymatic cleavage of \(\kappa\)-casein still occurs slowly.
Conversely, when the temperature is elevated and maintained above \(50^\circ\text{C}\), two major destabilizing events occur:
First, the active enzyme chymosin undergoes rapid thermal denaturation and loses its catalytic activity, preventing the hydrolysis of \(\kappa\)-casein.
Second, high temperatures alter the physical state of the casein micelles and soluble calcium phosphate, disrupting the hydrophobic interactions and calcium bridge formations essential for gel structure.
Therefore, maintaining the milk temperature above \(50^\circ\text{C}\) inactivates the rennet enzyme, which prolongs or completely prevents coagulation.

Step 3: Final Answer:
The rennet coagulation of casein is prolonged or prevented when the milk temperature is maintained above \(50^\circ\text{C}\).