Question

Match List-I with List-II.
List-I (Defect) & List-II (Causative metabolite)
(A) Putrid odour in butter & (I) acid and gas
(B) Frothiness in sour cream & (II) isovaleric acid
(C) Phenolic flavour in sterilized milk & (III) 3-methyl butanol
(D) Malty flavour & (IV) cresols

• (A) - (I), (B) - (II), (C) - (III), (D) - (IV)
• (A) - (II), (B) - (I), (C) - (IV), (D) - (III)
• (A) - (III), (B) - (II), (C) - (I), (D) - (IV)
• (A) - (IV), (B) - (III), (C) - (I), (D) - (II)

Hint:

To quickly solve matching questions, pair the most distinct terms first: "Malty flavour" always pairs with "3-methyl butanol", and "Putrid butter" always pairs with "isovaleric acid".

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Microbial degradation of constituents in milk and milk products generates specific volatile compounds.
Identifying these unique chemical metabolites helps diagnose the specific microbial contaminant responsible for quality defects.

Step 2: Detailed Explanation:
Let us analyze each pair systematically:
1. Putrid odour in butter (A): This defect is caused by the growth of psychrotrophic, lipolytic bacteria such as Pseudomonas putrefaciens on butter surfaces.
These bacteria hydrolyze lipids and proteins, producing volatile short-chain fatty acids, primarily isovaleric acid (II), which produces a sweaty, putrid, and cheese-like off-odor.
2. Frothiness in sour cream (B): Contamination of sour cream with gas-producing yeasts (such as Torulopsis or Saccharomyces) or coliform bacteria leads to active carbohydrate fermentation.
This metabolic pathway generates substantial amounts of organic acid and gas (\(\text{CO}_2\)) (I), resulting in a frothy, bubbling texture.
3. Phenolic flavour in sterilized milk (C): Spore-forming bacilli, particularly Bacillus circulans, can survive the sterilization process.
These bacteria decompose amino acids to produce volatile phenolic compounds, such as cresols (IV), which impart an unpleasant, medicinal, disinfectant-like flavor.
4. Malty flavour (D): This off-flavor is caused by Lactococcus lactis subsp. lactis biovar. maltigenes.
This organism deaminates the amino acid leucine to produce intermediate aldehydes and alcohols, specifically 3-methyl butanol (III), which yields a distinct malty or burnt-toast aroma.

Step 3: Final Answer:
Matching the defects with their causative metabolites results in the sequence: (A) - (II), (B) - (I), (C) - (IV), (D) - (III).