Vegetable fermentations: Abnormal fermentation of cabbage can produce a cheese-like odour. Which compound is most associated with this defect?

Introduction / Context:
Sauerkraut and other cabbage fermentations rely on lactic acid bacteria to produce desirable acidity, flavour, and texture. Process deviations can allow undesirable anaerobes to grow, forming odorous short-chain fatty acids (SCFAs) and gas. Recognizing the main chemical culprits behind off-odours helps troubleshoot fermentations and improve quality control.

Given Data / Assumptions:

• “Cheese-like” off-odours are linked to SCFAs produced by contaminating anaerobes (e.g., clostridia).
• Candidate acids include propionic, butyric, caproic, and valeric acids.
• The task is to identify the compound most typically implicated.

Concept / Approach:
Butyric acid (C4) is classically associated with rancid, cheesy, or putrid notes in vegetable and dairy products when formed by unwanted anaerobic fermentation. Propionic acid contributes to Swiss cheese aroma under controlled conditions, and caproic/valeric acids can impart goaty or sweaty notes, but butyric predominates as the textbook offender in abnormal cabbage fermentations.

Step-by-Step Solution:
Link abnormal anaerobic growth (e.g., Clostridium) to SCFA production. Identify the SCFA most strongly associated with cheese-like rancid odour: butyric acid. Select “Butyric acid” as the specific answer.

Verification / Alternative check:
Quality manuals for sauerkraut note that butyric fermentation produces strong cheese-like odours and soft texture, often accompanying gas pockets and slippage defects.

Why Other Options Are Wrong:

• Propionic acid: More characteristic of propionibacteria in cheese ripening, not the main defect in cabbage.
• Caproic/valeric acids: Can contribute off-notes but are less commonly singled out than butyric acid.
• All of these / Lactic acid only: Overbroad or incorrect; lactic acid is desired in normal fermentations.

Common Pitfalls:
Assuming any SCFA implies the same aroma impact; butyric acid’s low threshold makes it the most recognizable culprit.

Final Answer:
Butyric acid is most associated with a cheese-like odour in abnormal cabbage fermentation.