Rennin acts on

Options

A. milk charging casein into calcium paracaseinate at 7.2 -8.2 pH
B. protein in stomach
C. fat in intestine
D. milk changing casein into calcium paracaseinate at 1-3 pH

Explanation

**Step-by-Step Solution:**

1. **Understanding Renin**: Renin is an enzyme that is involved in the digestion of milk. It is secreted in an inactive form known as prorenin.

2. **Source of Renin**: Prorenin is secreted by the zymogen cells of the stomach.

3. **Activation of Prorenin**: Once prorenin is secreted, it is activated to renin by hydrochloric acid (HCl) present in the stomach.

4. **Function of Renin**: The primary function of renin is to act on milk, specifically on the protein casein.

5. **Conversion Process**: Renin converts casein into calcium paracaseinate, which is a curd-like substance.

6. **pH Consideration**: The question provides two options regarding the pH at which renin acts on milk:
- Option A: at a pH of 7.2 to 8.2
- Option D: at a pH of 1 to 3

7. **Determining the Correct pH**: Since HCl is a strong acid and creates a highly acidic environment in the stomach, renin acts effectively at a pH of 1 to 3, which corresponds to Option D.

8. **Conclusion**: Therefore, the correct answer to the question "Rennin acts on" is Option D: milk changing casein into calcium paracaseinate at a pH of 1 to 3.

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