Seafood microbiology — During chilled storage of shrimp (refrigerated, aerobic conditions), which microbial group is chiefly responsible for spoilage off-odors, slime, and surface discoloration?

Introduction / Context:
Spoilage of seafood at refrigeration temperatures is driven by psychrotrophic (cold-tolerant) microbes that grow on the surface and utilize readily available nitrogenous compounds. Understanding which organisms dominate under cold, aerobic storage helps in selecting the right control strategies (sanitation, glazing, modified-atmosphere packaging) to extend shelf life.

Given Data / Assumptions:

• Product: raw shrimp stored chilled (about 0–5°C) in air.
• Matrix is high in water activity and contains labile amino compounds and trimethylamine oxide.
• No specialized packaging (e.g., vacuum or high CO2) is assumed.

Concept / Approach:
At low temperatures and in the presence of oxygen, Gram-negative psychrotrophs, especially Pseudomonas spp., outcompete many other genera on seafood. They rapidly produce volatile sulfur compounds, amines, and slime-forming exopolymers, which translate to off-odors and textural degradation. Alternative groups listed either prefer different conditions (warmer temperatures, lower water activity) or are slower competitors on chilled seafood.

Step-by-Step Solution:

Verification / Alternative check:
Quality indices for seafood commonly track total viable counts and specific spoilage organisms like Pseudomonas and Shewanella; sensory spoilage correlates best with their population increases during chilled storage.

Why Other Options Are Wrong:

• Achromobacter: not the primary psychrotrophic spoiler of chilled shrimp.
• Micrococcus or Bacillus: grow slower at low temperature; Bacillus is spore-forming and more relevant after heat abuse.
• Molds/yeasts: require favorable surfaces; typically slower in cold, short-term storage compared with Pseudomonas.

Common Pitfalls:
Assuming the initial flora dictates spoilage regardless of temperature; at refrigeration, selection strongly favors psychrotrophs like Pseudomonas.

Final Answer:
Pseudomonas