Definition and meaning of emulsification of fats and how bile salts work
Fats are the long chain of carboxylic acids and are lighter than water. They float on a liquid medium like food in the intestine. The pancreas secretes pancreatic lipase. This enzyme is water soluble and cannot work on fat itself. To overcome the issue of solubility of fats, the liver secretes bile juice. Bile juice has two ends one hydrophilic and another lipophilic. Its hydrophobic end attaches to the water while the lipophilic property attaches to the fats. As a result, fat comes closer to the water molecule and the liquid becomes a suspension of fats and water. Now pancreatic lipase comes into action and breaks fats into a simple chain of fatty acid. Due to the attachment of fats with water, the fat also breaks into small sizes. We call it fat globules. The whole process of breaking fat into its globule and its suspension in water is termed as emulsification of fat.
The similarity in soap and bile salts:
This property of bile juice is similar to soap or detergent. Detergent has an affinity to both water and dirt particles which are composed of fats. Due to this when we shake a dirty cloth, dirt from the cloth goes into the soap solution; and we get a clean cloth.
This property of detergent and bile salt is a physical property and we call this property surfactant because detergent and bile salt brings two immiscible (insoluble) medium together as it lowers the surface tension.
A water drop takes the shape of a sphere when left alone. This property is seen more when the surface is oily. This happens because of water like own nearby molecule more than outer molecules. An inner molecule of water is attracted by water molecules from all side. While at the outer surface, there is more inward attraction than outward attraction. This creates an un-proportional pull at the surface. Since spherical shape has the lowest distance from molecules. So water droplet acquires the shape of the sphere. This un-proportional force is surface tension.
A surfactant balances the surface tension and brings two surfaces together. So we call bile salts and soap as a surfactant.