Question

Given below are two statements:
Statement (I): Heat stability of whole milk is reduced by homogenization.
Statement (II): Heat stability of milk is considerably improved with the presence of citrates, phosphates and urea.
In light of the above statements, choose the most appropriate answer from the options given below.

• A. Both Statement (I) and Statement (II) are true
• B. Both Statement (I) and Statement (II) are false
• C. Statement (I) is true but Statement (II) is false
• D. Statement (I) is false but Statement (II) is true

Hint:

To prevent coagulation during sterilization of concentrated milk, dairy processors add disodium phosphate or trisodium citrate as stabilizers. These salts bind excess calcium ions, restoring the mineral balance and protecting casein from heat gelation.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Heat stability refers to the capacity of milk to withstand high-temperature sterilization treatments without undergoing visible protein coagulation, gelation, or destabilization.
This stability is governed by the salt balance, mineral equilibrium, protein structure, and physical state of the fat globules in milk.

Step 2: Detailed Explanation:
Let us evaluate the physical and chemical factors affecting milk stability:
- Statement (I): Homogenization physically reduces the average diameter of fat globules, increasing their total surface area by several-fold.
- Because the original fat globule membrane material is insufficient to cover this newly formed surface, skim milk proteins (principally casein micelles) are adsorbed onto the new fat-water interface.
- These fat-bound casein complexes are more susceptible to thermal denaturation and aggregation, which reduces the overall heat stability of homogenized whole milk compared to unhomogenized milk. Thus, Statement (I) is true.
- Statement (II): The heat stability of casein micelles is highly sensitive to the concentration of free calcium ions (\(\text{Ca}^{2+}\)) in the serum phase.
- Citrates and phosphates act as natural mineral chelators that sequester free calcium ions, preventing them from forming salt bridges that destabilize proteins.
- Additionally, urea acts as a natural buffer and protein stabilizer in milk, preventing heat-induced cross-linking of proteins.
- Consequently, the presence of these substances considerably improves the heat stability of milk. Thus, Statement (II) is true.
Since both statements are true, the correct option is (A).

Step 3: Final Answer:
Both Statement (I) and Statement (II) are true.