Question

The yield of acid casein ranges between ________ to _______ from skim milk

• A. 2.2 to 2.4%
• B. 2.0 to 2.2%
• C. 4.0 to 4.5%
• D. 2.8 to 3.2%

Hint:

As a rule of thumb, remember that skim milk contains about 3% casein. This will help you quickly estimate the correct range for casein yield in multiple-choice questions.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
The question asks for the typical yield (in percent by weight) of acid casein produced from skim milk. The yield depends directly on the amount of casein protein present in the skim milk.
Step 2: Key Formula or Approach:
\[ \text{Casein Content} \approx \text{Total Protein in Skim Milk} \times 0.80 \] The yield will be slightly higher than the actual casein content due to co-precipitation of some minerals and residual moisture, but it is primarily determined by the protein level.
Step 3: Detailed Explanation:
Skim milk typically contains between 3.2% and 3.8% total protein. Casein constitutes about 80% of this total protein.
For milk with 3.4% protein: Casein content \(= 3.4 \times 0.8 = 2.72%\).
For milk with 3.8% protein: Casein content \(= 3.8 \times 0.8 = 3.04%\).
Therefore, the theoretical yield of pure casein would be in the range of 2.7% to 3.1%. The actual industrial yield of acid casein (which includes some minerals) aligns well with this.
Let's check the options:
(A) 2.2 to 2.4%: This would correspond to very low-protein milk, below average.
(B) 2.0 to 2.2%: Very low.
(C) 4.0 to 4.5%: Too high, skim milk does not contain this much casein.
(D) 2.8 to 3.2%: This range accurately reflects the yield from average to high-protein skim milk. A typical yield figure often quoted is around 3 kg of casein per 100 kg of skim milk, which is 3%.
Step 4: Final Answer:
The expected yield of acid casein from skim milk falls in the range of 2.8% to 3.2%.