With reference to the digestion of food in human beings, consider the following statements: I. Digestion of the milk protein, casein is initiated in the duodenum with its coagulation. II. Trypsin hydrolyses casein into paracasein and whey proteins Which of these statements is/are correct?

Digestion of the milk protein casein is initiated in the stomach, not the duodenum. In the stomach, gastric glands secrete hydrochloric acid and enzymes like pepsin and rennin (chymosin) [c1, t2]. Rennin, primarily active in infants, initiates the coagulation or curdling of milk by converting soluble casein into paracasein in the presence of calcium [t2, t3, t10]. This process prevents milk from flowing too rapidly through the stomach, ensuring efficient protein digestion [t7]. Statement II is incorrect because trypsin is a pancreatic enzyme that acts in the small intestine to hydrolyze proteins into proteoses, peptones, and peptides [c2, t2]. It is rennin (or pepsin in adults) that is responsible for the initial conversion of casein to paracasein in the gastric phase [t2, t3]. Therefore, both statements are scientifically inaccurate regarding the site of initiation and the specific enzyme responsible for paracasein formation.

Sources

1. [1] Science , class X (NCERT 2025 ed.) > Chapter 5: Life Processes > Activity 5.3 > p. 85
2. [2] Science , class X (NCERT 2025 ed.) > Chapter 5: Life Processes > Activity 5.3 > p. 86