Question

Which of the following is NOT a source for indigenous enzymes in milk?

• A. Blood plasma
• B. Milk fat globule membrane
• C. Somatic cells
• D. Casein micelle

Hint:

Indigenous enzymes are biological catalysts that must originate from cellular or tissue sources (such as blood plasma, cellular membranes (MFGM), or leukocytes).
Structural protein aggregates like casein micelles are not sources of these enzymes.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Indigenous enzymes in milk are those naturally synthesized by the animal and secreted into the milk.
These enzymes can originate from various physiological sources within the mammary gland or from systemic circulation.

Step 2: Detailed Explanation:
Let us evaluate the physiological origins of milk enzymes:
- (A) Blood plasma: Several enzymes (such as plasmin, the major protease) enter milk directly from the blood plasma via paracellular pathways.
- (B) Milk fat globule membrane (MFGM): During secretion, fat globules are enveloped by the apical membrane of the mammary secretory cell.
This membrane (MFGM) is highly rich in membrane-bound enzymes, such as alkaline phosphatase and xanthine oxidase.
- (C) Somatic cells: White blood cells (leukocytes) and epithelial cells shed into the milk contain lysosomes rich in enzymes like catalase and lysozyme.
- (D) Casein micelle: The casein micelle is a structural, colloidal aggregate of milk proteins (caseins, calcium, and phosphate) designed to transport amino acids and minerals.
It is a product of protein synthesis and is not a biological or cellular source of enzymes (although some enzymes, like plasmin, may adsorb onto it, the micelle itself is not the source).
Therefore, the casein micelle is not a source of indigenous enzymes in milk.

Step 3: Final Answer:
The casein micelle is not a source for indigenous enzymes in milk.