Question

The flocculation of casein micelle during cheese making cannot occur if the temperature of the milk is maintained below

• A. 35 °C
• B. 20 °C
• C. 30 °C
• D. 40 °C

Hint:

Renneting Temperature Thresholds: Flocculation and Curd Aggregation (Secondary Phase) CEASES BELOW 20$^\circ\text{C}$ (Used in Cold Renneting). Optimum clotting = $30^\circ - 35^\circ ext{C}$.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Thermal kinetics of the secondary phase of rennet clotting: the non-enzymatic hydrophobic aggregation of para-casein micelles exhibits extreme temperature sensitivity ($Q_{10} pprox 12 - 16$), halting completely below $18^\circ - 20^\circ ext{C}$ (basis of cold renneting).
Key Formula or Approach:
\[ \text{Secondary Aggregation Phase: } Q_{10} \approx 12 - 16 \quad \implies \quad \text{Aggregation Rate } \rightarrow 0 \quad \text{when } T \le \mathbf{18^\circ - 20^\circ\text{C}} \]

Step 2: Detailed Explanation:
In cheese manufacturing thermodynamics and cold renneting technology:
- While the primary enzymatic phase (cleavage of $\kappa$-casein) proceeds normally at cold temperatures ($0^\circ - 15^\circ ext{C}$),
- The Secondary Phase (Flocculation, Aggregation, and Gelation of Para-Casein Micelles):
1. Is driven predominantly by hydrophobic interactions and calcium bridging between para-casein micelles.
2. Hydrophobic bond strength drops precipitously with decreasing temperature, resulting in an exceptionally high temperature coefficient ($Q_{10} \approx 12\text{ to } 16$).
3. Below 20°C (18°C to 20°C) (B), casein micelle flocculation and clotting cannot occur at all.
- This principle is utilized in the 'Cold Renneting Process' where rennet acts on milk at $4^\circ - 10^\circ ext{C}$ without coagulation, followed by instantaneous curd gelation upon rapid warming to $30^\circ - 32^\circ ext{C}$.

Step 3: Final Answer:
Hence, flocculation cannot occur if temperature is maintained below 20 °C, matching option (B).