What is the emulsifier present in milk that makes it stable?

Casein

The correct answer is option 1. Casein.

Casein is a type of protein found in milk, comprising about 80% of the total protein content. It is an amphiphilic molecule, meaning it has both hydrophilic (water-attracting) and hydrophobic (water-repelling) regions. This molecular structure allows casein to interact effectively with both water and fat molecules.

In milk, casein molecules surround and stabilize fat droplets, forming what is known as a colloidal suspension. The hydrophilic regions of casein interact with water molecules, while the hydrophobic regions interact with the fat droplets. This creates a protective layer around the fat droplets, preventing them from coalescing and separating from the rest of the liquid. As a result, the fat remains dispersed throughout the milk, giving it a homogeneous appearance and preventing the formation of a cream layer.

The stability of milk as an emulsion is largely due to the presence of casein as a natural emulsifying agent. This property is essential for various dairy products and contributes to their texture, mouthfeel, and overall quality.