Question

Malty defect in butter is due to the formation of

• A. 2- dimethylbutanal
• B. 3- methylbutanal
• C. Diacetyl
• D. Acetoin

Hint:

Dairy Flavor Chemistry:
MALTY Flavor = 3-METHYLBUTANAL (Derived from Leucine by L. lactis biovar maltigenes).
BUTTER Flavor = DIACETYL (2,3-butanedione from citrate).

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Aroma chemistry and Strecker amino acid degradation: Lactococcus lactis ssp. lactis biovar maltigenes transaminates and decarboxylates dietary L-leucine into 3-methylbutanal (isovaleraldehyde), producing an intense malty off-flavor.
Key Formula or Approach:
\[ \text{L-Leucine} \xrightarrow{\text{Aminotransferase}} \alpha\text{-Ketoisocaproic Acid} \xrightarrow{\text{Decarboxylase}} \mathbf{3\text{-Methylbutanal (Malty Aroma)}} \]

Step 2: Detailed Explanation:
In dairy flavor chemistry and microbial off-flavors:
- Malty Flavour Defect in milk, cream, and butter (imparting an unpalatable, pungent toasted-malt cooked-grain flavor):
- Caused by contamination with Lactococcus lactis ssp. lactis biovar maltigenes (formerly Streptococcus lactis var. maltigenes).
- The organism enzymatically converts the branched-chain amino acid L-Leucine via transamination to $\alpha$-ketoisocaproate, followed by thiamine-dependent decarboxylation to generate 3-Methylbutanal (Isovaleraldehyde) (B) and its alcohol 3-methylbutanol, which possess an extremely low sensory threshold causing the pathognomonic malty defect.

Step 3: Final Answer:
Therefore, malty defect is due to the formation of 3- methylbutanal, matching option (B).