Protein putrefaction under anaerobic conditions: Anaerobic degradation of proteins by bacteria and fungi commonly produces which foul-smelling metabolites associated with food spoilage and tissue putrefaction?

Introduction / Context:
In food microbiology and clinical settings, the anaerobic breakdown of proteins and amino acids leads to distinctive odors and discoloration. Recognizing the typical metabolites helps in diagnosing spoilage, identifying causative organisms, and designing control strategies.

Given Data / Assumptions:

• Anaerobic conditions (limited oxygen), typical of deep tissues, sealed packages, or sediments.
• Proteinaceous substrates rich in sulfur- and tryptophan-containing amino acids.
• Bacterial and fungal consortia participate in putrefaction.

Concept / Approach:
Microbes deaminate and decarboxylate amino acids, reducing sulfur-containing residues to hydrogen sulfide (H2S) and forming volatile sulfur compounds such as mercaptans (thiols). Tryptophan metabolism yields indole and skatole. These compounds impart characteristic rotten, fecal, or cabbage-like odors, and H2S may blacken metals or react with iron to form dark precipitates.

Step-by-Step Solution:
Identify key amino acids: cysteine and methionine (sulfur), tryptophan (indole formation). Map pathways: reduction to H2S; enzymatic cleavage yielding mercaptans and indole. Relate to observed signs: blackening, sulfurous smell, fecal/musty odors. Select the inclusive option capturing both sulfur compounds and indole.

Verification / Alternative check:
Lead acetate strips detect H2S; Kovac’s reagent detects indole; gas chromatography can profile volatile sulfur compounds, confirming metabolic byproducts.

Why Other Options Are Wrong:

• Only mercaptans and indole: incomplete because H2S is also characteristic.
• Only H2S: misses other hallmark putrefactive volatiles.
• None: incorrect; these metabolites are classic markers.

Common Pitfalls:
Attributing all off-odors to a single metabolite; in reality, a bouquet of compounds arises from complex microbial ecosystems.

Final Answer:
both (a) and (b)