Question

Compound responsible for fruity flavor

• A. 3-methylbutanol
• B. 2-methoxy formazine
• C. Ethylbutanoate
• D. Trimethylamine

Hint:

To identify specific off-flavors and their chemical causes:
- Fruity flavor \(\rightarrow\) Volatile esters, primarily Ethylbutanoate (produced by Pseudomonas fragi).
- Malty flavor \(\rightarrow\) 3-methylbutanol.
- Fishy flavor \(\rightarrow\) Trimethylamine.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Contamination of raw or processed milk with psychrotrophic bacteria can lead to various enzymatic defects during cold storage.
These bacteria produce extracellular lipases and esterases that hydrolyze milk lipids and catalyze the synthesis of volatile organic compounds, resulting in distinct off-flavors.

Step 2: Detailed Explanation:
A fruity off-flavor in milk (often described as resembling apples, pineapples, or strawberries) is caused by the synthesis of volatile esters.
Gram-negative psychrotrophic bacteria, such as Pseudomonas fragi, produce active esterases during growth in milk at refrigeration temperatures.
These esterases catalyze the esterification of short-chain fatty acids (derived from milk fat lipolysis) with ethanol (derived from bacterial carbohydrate fermentation).
-Causative Compound:
The ester primarily responsible for this fruity, sweet, pineapple-like off-flavor is ethyl butanoate (also known as ethyl butyrate).
Because this ester has an extremely low sensory threshold, even trace amounts produce a distinct fruity aroma.
Let us review the other options to understand their sensory roles:
- 3-methylbutanol: An alcohol produced by Lactococcus lactis subsp. lactis biovar. maltigenes that causes a malty off-flavor.
- Trimethylamine: A volatile amine associated with stale, fishy off-flavors in milk and milk powder.
- 2-methoxy formazine: A compound not associated with natural or bacterial off-flavors in milk.

Step 3: Final Answer:
The compound responsible for the fruity off-flavor in milk is ethylbutanoate, which corresponds to Option (C).