Topics:
Animal Refresher, Dairy Science
Total Nitrogen in Milk
Which of the following sentence(s) is/are true about total nitrogen present in milk?
- Both: Casein constitutes about 80% of total nitrogen; NPN constitutes about 5% of total nitrogen — Correct Answer
- Casein constitutes about 80% of the total nitrogen only
- NPN constitutes about 5% of the total nitrogen only
- None of the above
Explanation:
Correct Answer: Both statements are true
- Casein constitutes about 80% of total nitrogen: Casein is the predominant protein in milk, making up approximately 80% of all the nitrogenous compounds. The remaining ~20% is whey protein nitrogen and non-protein nitrogen (NPN).
- NPN constitutes about 5% of total nitrogen: NPN (Non-Protein Nitrogen) includes urea, creatine, creatinine, uric acid, amino acids, ammonia, and other small nitrogen-containing compounds. These are not true proteins but contribute ~5% of total milk nitrogen.
Nitrogen Distribution in Milk
- Casein nitrogen: ~80% of total N
- Whey protein nitrogen: ~15% of total N (α-lactalbumin, β-lactoglobulin)
- Non-protein nitrogen (NPN): ~5% of total N
Protein Content
- Cow milk protein: ~3.4% (3% casein + 0.4% whey proteins)
- Buffalo milk protein: ~3.9% (4.3% casein)
- Biological value of cow milk: 86.90; buffalo milk: 84.04
- Milk proteins are particularly rich in Lysine and Valine.
📚 About this Topic — Animal Refresher
This multiple choice question is from Animal Refresher, Dairy Science. It has 4 options with a detailed explanation of the correct answer. Practice more MCQs from Animal Refresher to strengthen your preparation.
