Nature of K-Casein (Kappa-Casein) in Milk

K-casein (κ-casein) present in milk is:

Correct Answer: Calcium-insensitive casein

K-casein (κ-casein) is calcium-insensitive casein — it is NOT precipitated by calcium ions. This is a defining feature that distinguishes it from the other major casein fractions.

Types of Casein Proteins in Milk

• Three types: α-casein, β-casein, γ-casein
• α-casein consists of two components:
  • αs-casein (alpha-s casein): Calcium-sensitive — precipitated by calcium ions.
  • κ-casein (K-casein): Calcium-insensitive — NOT precipitated by calcium ions.

Role of K-Casein

• K-casein acts as a protective colloid — it stabilizes the casein micelle in milk by preventing calcium-mediated aggregation.
• When K-casein is hydrolyzed by chymosin (rennet), the micelle destabilizes and coagulation (curd formation) occurs — this is the basis of cheese making.

Casein in Milk — Summary

• Casein exists in milk as calcium-caseinate-phosphate complex (colloidal suspension).
• Casein = 80% of total milk protein; responsible for white colour and viscosity of milk.
• Cow milk casein: 3%; Buffalo milk casein: 4.3%.