Milk discoloration — pigment defect produced by Pseudomonas syncyanea What characteristic color change does Pseudomonas syncyanea produce in milk when grown in pure culture under chill conditions?

Introduction / Context:
Pseudomonads are common psychrotrophic spoilers in raw and pasteurized milk held at refrigeration temperatures. Many produce pigments or enzymes (proteases, lipases) that cause visible and sensory defects, helping quality teams pinpoint the contamination source.

Given Data / Assumptions:

• Organism: Pseudomonas syncyanea, a pigment-forming psychrotroph.
• Matrix: milk under chill storage.
• Outcome: characteristic discoloration pattern.

Concept / Approach:
As its epithet suggests, P. syncyanea is associated with bluish/cyan pigmentation. In pure culture, it leads to a bluish gray hue that may progress toward brownish tones as the product oxidizes or as mixed flora develop. Recognizing this signature helps separate Pseudomonas-driven issues from coliform or lactic spoilage.

Step-by-Step Solution:
Link the species name (“syncyanea”) with cyan/blue pigmentation.Identify the typical progression in milk: bluish gray shifting toward brownish under certain conditions.Select the option that captures this range most accurately.

Verification / Alternative check:
Cold storage microbiology references list blue/blue-gray defects in milk due to certain Pseudomonas spp., including P. syncyanea.

Why Other Options Are Wrong:
Reversing the description (brownish to bluish) misrepresents the classical observation; “gray to brown” and “yellow” better fit other spoilage organisms; pink rings suggest Serratia or other red-pigmented bacteria, not P. syncyanea.

Common Pitfalls:
Misattributing lipolysis-induced rancidity (flavor) to pigment issues; assuming all psychrotrophs yield the same visual cues.

Final Answer:
Bluish gray to brownish color in milk in its pure form.