Question

Which of the following acts as a precusor for the production of acetaldehyde in yoghurt?

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

Hint:

Acetaldehyde, the characteristic flavor compound in yoghurt, is produced primarily from threonine via the action of the starter culture enzyme threonine aldolase.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Acetaldehyde is the primary volatile compound responsible for the characteristic green, pungent, and typical flavor of yoghurt.
It is produced during milk fermentation by symbiotic yoghurt starter cultures, specifically Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus.

Step 2: Detailed Explanation:
Although yoghurt bacteria can synthesize acetaldehyde via multiple metabolic pathways (such as from glucose or pyruvate), the primary pathway involves the cleavage of amino acids:
The amino acid threonine serves as the direct precursor for acetaldehyde production.
Yoghurt starter cultures express the enzyme threonine aldolase.
This enzyme catalyzes the cleavage of L-threonine into glycine and acetaldehyde:
\[ \text{L-Threonine} \xrightarrow{\text{Threonine aldolase}} \text{Glycine} + \text{Acetaldehyde} \] Other amino acids like serine, lysine, and methionine are metabolized through different pathways and do not serve as direct precursors for acetaldehyde synthesis in these starter cultures.

Step 3: Final Answer:
Consequently, threonine is the precursor for acetaldehyde production in yoghurt.