Question

Which one of the following enzymes carries out the initial step in the digestion of milk in humans?
A. Pepsin
B. Rennin
C. Lipase
D. A and B

Answer 1

Hint: Human consume milk as a part of their diet. They drink the milk obtained from different animals. Milk contains various nutrients and compounds. Milk contains a sugar called lactose which is digested by specific digestive enzymes.

Complete answer:
The gastrointestinal tract, after ingestion of milk, works to digest and absorb the different nutrients present in the milk. The process of digestion of milk starts in the mouth. In the mouth, the saliva is slightly acidic in nature and combines with milk. When saliva combines with milk, it causes milk to break down. When milk is swallowed, it moves down the oesophagus and reaches the intestine.

The stomach contains several enzymes which are known as the gastric juices. The gastric juices in the stomach breaks down the milk. The enzyme pepsin acts on the components of milk by breaking down the protein molecules into smaller fragments. These fragments are then moved to the next part of the digestion that is carried out in the small intestines. Pepsin enzyme acts on the milk protein part which is the water soluble caseinogen. Caseinogen is converted into soluble casein. Casein then combines with the calcium salts to get converted into insoluble calcium paracaseinate. It then is readily digested through enzymatic reactions.

Renin is a protein digesting enzyme which acts on milk and causes curdling of milk. The process of curdling milk occurs by transforming caseinogen into insoluble casein. It is not found in adult humans but is found in infants. In infants and small children, the renin causes coagulation of milk and assists in digestion of milk. It is found in curd-chewing animals. It is also known as chymosin.

Lipase enzyme acts on the hydrolysis of fats. It performs an important function of digestion of lipids and fatty acid in living organisms. It is found in the pancreas, mouth and stomach. This enzyme is present in the pancreatic secretions which are responsible for fat digestion.

Hence, the correct answer is option (D).

Note: The digestion of milk in humans takes place in the stomach and small intestines. In the stomach, the protein constituent of milk is acted upon by the enzyme pepsin. The enzyme pepsin acts on the protein and breaks it down into smaller components and are readily absorbed by the cells. The process of breaking down of proteins produces casein which again gets converted into compounds that are enzymatically digested. However, in infants and small children, renin causes coagulation of milk.