Question

3-methylbutanal responsible for malty flavour, is derived from

• A. Leucine
• B. Lysine
• C. Methionine
• D. Threonine

Hint:

Amino Acid Flavor Precursors:
LEUCINE $\rightarrow$ 3-Methylbutanal (Malty flavor).
ISOLEUCINE $\rightarrow$ 2-Methylbutanal.
VALINE $\rightarrow$ 2-Methylpropanal.
METHIONINE $\rightarrow$ Methional (Sunlight flavor).

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Biochemical Strecker degradation pathway: L-leucine is transaminated to $lpha$-ketoisocaproic acid and subsequently decarboxylated by thiamine pyrophosphate-dependent decarboxylase to 3-methylbutanal.
Key Formula or Approach:
\[ \text{L-Leucine } \left(\text{(CH}_3)_2\text{CH-CH}_2\text{-CH(NH}_2\text{)COOH}\right) \xrightarrow{\text{Transamination}} \alpha\text{-Ketoisocaproate} \xrightarrow{-\text{CO}_2} \mathbf{3\text{-Methylbutanal}} \]

Step 2: Detailed Explanation:
Biochemical origin of malty aroma in dairy products:
- The compound 3-Methylbutanal (Isovaleraldehyde) is synthesized by Lactococcus lactis subsp. lactis biovar maltigenes from the essential branched-chain amino acid L-Leucine (A):
1. Step 1 (Transamination): Branched-chain aminotransferase converts L-leucine into $\alpha$-ketoisocaproic acid.
2. Step 2 (Decarboxylation): $\alpha$-Keto acid decarboxylase cleaves $\text{CO}_2$, yielding 3-Methylbutanal.
3. (Compare: Isoleucine yields 2-methylbutanal; Valine yields 2-methylpropanal/isobutyraldehyde; Methionine yields methional).

Step 3: Final Answer:
Therefore, 3-methylbutanal is derived from Leucine, matching option (A).