Question

Musty potato aroma in milk is the result of the production of..................caused by the contamination of milk with Gram negative bacteria.

• A. 2-methoxy-3-isopropylpyrazine
• B. Dimethyl sulphide
• C. Diethyl sulphide
• D. 3-methylbutanol

Hint:

Associate alkylpyrazines, specifically 2-methoxy-3-isopropylpyrazine, with Pseudomonas taetrolens contamination and the characteristic "musty potato" or "earthy" spoilage defect.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Gram-negative psychrotrophic bacteria are significant spoilage organisms in the dairy industry because they can grow at refrigeration temperatures.
These bacteria produce various volatile organic compounds as secondary metabolites during their growth in raw or pasteurized milk.
These compounds often impart distinct off-flavors and off-odors, which degrade the organoleptic quality of the milk.

Step 2: Detailed Explanation:
The musty potato off-flavor in milk and dairy products is a well-documented spoilage defect.
This specific defect is primarily associated with the growth of Gram-negative, psychrotrophic, aerobic rods belonging to the genus Pseudomonas.
The species Pseudomonas taetrolens (formerly Pseudomonas graveolens) is particularly known for producing this defect.
During its metabolic activity in milk, this bacterium synthesizes alkylated pyrazine derivatives.
The principal compound responsible for this specific musty, earthy, potato-like aroma is 2-methoxy-3-isopropylpyrazine.
This compound has an exceptionally low odor threshold, meaning it can be detected by human senses even at extremely low concentrations in the parts-per-trillion range.
Let us review the other options:
- Dimethyl sulphide is associated with light-induced or cooked off-flavors in milk.
- Diethyl sulphide is a volatile sulfur compound that contributes to putrid or cabbage-like odors.
- 3-methylbutanol is an alcohol that contributes to a malty off-flavor, typically produced by Lactococcus lactis subsp. lactis biovar. maltigenes.

Step 3: Final Answer:
The volatile compound responsible for the musty potato aroma in contaminated milk is 2-methoxy-3-isopropylpyrazine.