Question

Which one of the following can act as a source of cooked flavour in case of boiled milk?

• A. Butyric acid
• B. Methionine
• C. Lactose
• D. N-Acetyl neuraminic acid

Hint:

Heated Milk Flavor Chemistry: COOKED FLAVOUR is generated by sulfur volatiles ($\text{H}_2\text{S}$, methanethiol) released from METHIONINE and Cysteine upon $\beta$-lactoglobulin denaturation ($> 75^\circ\text{C}$).

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Thermally induced cooked flavor in heated milk: thermal unfolding of whey proteins ($eta$-lactoglobulin) exposes free sulfhydryl (-SH) groups and thermal degradation of sulfur amino acids (methionine, cysteine) generates volatile hydrogen sulfide ($ ext{H}_2 ext{S}$) and methanethiol.
Key Formula or Approach:
\[ \text{Heated Milk (} T > 75^\circ\text{C)}: \beta\text{-Lg Denaturation} + \text{Methionine Degradation} \longrightarrow \mathbf{\text{H}_2\text{S} + \text{Methanethiol}} \implies \mathbf{Cooked \text{ } Flavour} \]

Step 2: Detailed Explanation:
In milk chemistry and the thermal processing of fluid milk:
- When milk is heated above $75^\circ - 80^\circ ext{C}$ (boiled milk, pasteurized HTST/UHT milk), it develops a characteristic Cooked Flavour Cooked Aroma:
1. Heat denatures $\beta$-Lactoglobulin, exposing reactive free sulfhydryl groups (-SH) that were previously buried in the hydrophobic core of the native protein.
2. Thermal Strecker degradation and cleavage of sulfur-containing amino acids—principally Methionine (B) and Cysteine—liberates volatile sulfur aroma compounds, including Hydrogen Sulfide ($\text{H}_2\text{S}$), Methanethiol, and Dimethyl Sulfide.
- These volatile sulfur compounds possess intense aroma potency, providing the primary chemical origin of the cooked flavor in boiled milk.

Step 3: Final Answer:
Therefore, Methionine acts as a source of cooked flavour, matching option (B).