Total Nitrogen in Milk

Which of the following sentence(s) is/are true about total nitrogen present in milk?

Correct Answer: Both statements are true

1. 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).
2. 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.