Question

The most stable component in milk in terms of its quantity is

• A. Fat
• B. Protein
• C. Lactose
• D. Solid-not-fat

Hint:

Lactose is the primary osmotic regulator of milk, maintaining osmotic pressure equal to that of blood plasma.
This physiological constraint prevents lactose concentration from fluctuating, making it the most stable component of milk.
In contrast, fat is the most variable component.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Milk is a complex biological fluid composed of water, fat, proteins (caseins and whey proteins), lactose (milk sugar), and minerals (ash).
The concentration of these constituents varies significantly based on breed, species, stage of lactation, health status, and nutrition of the animal.
The physiological regulation of milk synthesis ensures that certain components remain highly constant to maintain osmotic equilibrium with blood.

Step 2: Detailed Explanation:
Let us analyze the stability of different milk components:
- Lactose (milk sugar) is a disaccharide synthesized in the mammary gland by the enzyme lactose synthase.
Lactose acts as the primary osmotic regulator of milk.
Since the mammary gland membrane is permeable to water, water is drawn into the alveolar lumen to maintain the osmotic pressure of milk equal to that of blood plasma.
Any decrease in lactose synthesis results in a corresponding decrease in water secretion (total milk volume), keeping the concentration of lactose extremely stable (typically around 4.6% to 4.9% in bovine milk).
This make lactose the most stable and least variable component of milk under normal physiological conditions.
- Milk fat is the most variable component, fluctuating widely with the animal's diet, fiber intake, stage of lactation, and milking interval.
- Proteins and solid-not-fat (SNF) also exhibit moderate variations compared to the highly regulated lactose concentration.

Step 3: Final Answer:
The most stable component in milk in terms of its quantity is lactose.