Question

Which chemical groups are responsible for cooked flavour of milk ?

• A. Amine groups
• B. Suplhydryl groups
• C. Hydroxygroups
• D. Reducing moieties

Hint:

The development of a cooked flavor in milk is directly linked to the denaturation of \(\beta\)-lactoglobulin, which begins at \(74\ ^\circ\text{C}\) and exposes active sulfhydryl (-SH) groups.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
When milk is heated to high temperatures (above \(74\ ^\circ\text{C}\)), it develops a characteristic "cooked" or "heated" flavor.
This flavor is caused by the release of volatile sulfur compounds from the denaturation of whey proteins.

Step 2: Detailed Explanation:
Whey proteins, particularly \(\beta\)-lactoglobulin and proteins of the fat globule membrane, are rich in sulfur-containing amino acids like cysteine.
Under normal conditions, these sulfur groups are folded inside the protein structure.
However, when milk is heated above \(74\ ^\circ\text{C}\), these proteins denature and unfold, exposing active sulfhydryl (thiol, -SH) groups to the surrounding milk.
These exposed sulfhydryl groups undergo chemical reactions that release volatile compounds, such as hydrogen sulfide (\(H_2S\)).
These volatile compounds are directly responsible for the characteristic cooked aroma and flavor of heated milk.
While sulfhydryl groups act as natural antioxidants that protect milk from oxidation, they also cause this cooked flavor.
Amine, hydroxy, and reducing groups do not contribute to this cooked flavor.

Step 3: Final Answer:
The chemical groups responsible for the cooked flavor of milk are Sulfhydryl (Suplhydryl) groups.