Question

Choose the correct answer from the options given below with respect to the order of heat stability of the whey proteins as measured by loss of solubility, is

• A. \(\beta\)-lactoglobulin \(>\) \(\alpha\)-lactalbumin \(>\) bovine serum albumin \(>\) immunoglobulins
• B. Immunoglobulins \(>\) \(\beta\)-lactoglobulin \(>\) \(\alpha\)-lactalbumin \(>\) bovine serum albumin
• C. Immunoglobulins \(>\) bovine serum albumin \(>\) \(\beta\)-lactoglobulin \(>\) \(\alpha\)-lactalbumin
• D. \(\alpha\)-lactalbumin \(>\) \(\beta\)-lactoglobulin \(>\) bovine serum albumin \(>\) immunoglobulins

Hint:

Remember that \(\alpha\)-lactalbumin has the unique ability to thermally renature (refold) after cooling, making it the most heat-stable whey protein, while large, complex immunoglobulins are the most heat-sensitive.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Whey proteins are globular proteins that are highly sensitive to heat. When subjected to thermal treatments, they undergo unfolding (denaturation), exposing hydrophobic groups and sulfhydryl groups, which leads to aggregation and a subsequent loss of solubility.

Step 2: Detailed Explanation:
The heat stability of individual whey proteins (defined as their resistance to heat-induced denaturation and loss of solubility) varies significantly due to their molecular structures:

• \(\alpha\)-Lactalbumin: This is the most heat-stable major whey protein. Its denaturation is highly reversible because it contains four stabilizing disulfide bonds and binds calcium, which helps the protein refold into its native state upon cooling.

• \(\beta\)-Lactoglobulin: This is moderately heat-stable. It contains two disulfide bonds and one free sulfhydryl group (\(\text{--SH}\)) that becomes highly reactive above \(65^\circ\text{C}\), causing irreversible aggregation with other proteins.

• Bovine Serum Albumin (BSA): This is a large, complex protein that denatures and aggregates at relatively lower temperatures, making it quite heat-sensitive.

• Immunoglobulins (Igs): These are very large, complex multi-subunit glycoproteins with low thermal stability. They are the most heat-sensitive whey proteins and undergo rapid, irreversible denaturation and loss of solubility at the lowest temperature range (\(60\text{--}65^\circ\text{C}\)) among those listed.
Therefore, the decreasing order of heat stability (from most stable to least stable) is:
\[ \alpha\text{-lactalbumin} > \beta\text{-lactoglobulin} > \text{bovine serum albumin} > \text{immunoglobulins} \]

Step 3: Final Answer
The correct order of heat stability of the whey proteins is \(\alpha\)-lactalbumin \(>\) \(\beta\)-lactoglobulin \(>\) bovine serum albumin \(>\) immunoglobulins.