Milk Constituents Responsible for Depressing Freezing Point

Which constituents are primarily responsible for depressing the freezing point of milk?

Correct Answer: Lactose and Chloride

Lactose and Chloride are primarily responsible for depressing the freezing point of milk below 0°C.

Why Freezing Point of Milk is Below 0°C

• Pure water freezes at 0°C.
• Milk has dissolved solutes (mainly lactose and chloride salts) which lower the freezing point through the colligative property of freezing point depression.
• Freezing point of milk: −0.535°C to −0.550°C

Practical Application

• Addition of 1% water raises the freezing point by 0.006°C.
• Therefore, freezing point measurement is the best method to detect water adulteration.
• Mastitis milk shows normal freezing point (unlike specific gravity which changes).