Question

Match List-I with List-II.
List-I (Discolouration/Off-flavour) & List-II (Causative Organism)
(A) Fruity flavour & (I) Pseudomonas syncyanea
(B) Blue colour & (II) Pseudomonas synxantha
(C) Yellow colour & (III) Pseudomonas fragi
(D) Greenish Colour & (IV) Pseudomonas fluorescens

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

Hint:

To remember this:
- fragi \(\rightarrow\) fragrant/fruity.
- syncyanea \(\rightarrow\) cyan (blue).
- synxantha \(\rightarrow\) xantho (yellow).
- fluorescens \(\rightarrow\) green fluorescence.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Psychrotrophic bacteria belonging to the genus Pseudomonas are the most common cause of post-pasteurization contamination and spoilage in cold-stored milk.
They synthesize volatile enzymes and lipid-soluble pigments that produce characteristic discolorations and off-flavors.

Step 2: Detailed Explanation:
Let us match each defect with its specific causative species:
1. Fruity flavour (A): Pseudomonas fragi (III) is highly active in cold-stored milk.
It synthesizes extracellular esterases that esterify free fatty acids with ethanol, producing volatile ethyl esters (such as ethyl butyrate and ethyl hexanoate), which impart a sweet, apple- or strawberry-like fruity aroma.
2. Blue colour (B): Pseudomonas syncyanea (I) produces a greyish-blue pigment called pyocyanin.
In raw milk, when this organism grows alongside acid-producing bacteria like Lactococcus lactis, the acid turns the greyish pigment into a distinct, bright blue discoloration.
3. Yellow colour (C): Pseudomonas synxantha (II) produces a water-soluble yellow pigment.
It hydrolyzes milk fat and proteins, particularly on the cream layer, leaving a bright yellow surface discoloration.
4. Greenish Colour (D): Pseudomonas fluorescens (IV) is notorious for producing a water-soluble, yellow-green fluorescent pigment called pyoverdine (or fluorescein) under iron-limiting conditions, giving milk a fluorescent greenish-yellow hue.

Step 3: Final Answer:
Matching the pairs correctly yields: (A) - (III), (B) - (I), (C) - (II), (D) - (IV).