Canning microbiology — expected spoilage in medium-acid foods (pH 5.3 to 4.5) Medium-acid, canned foods with pH between 5.3 and 4.5 are most likely to undergo which specific type of spoilage if processing or storage conditions are inadequate?

Introduction / Context:
Canned-food stability is strongly governed by pH class. Medium-acid foods (pH 5.3–4.5) sit in a range where some sporeformers remain a risk, especially thermophilic aciduric organisms that do not produce gas, leading to subtle souring without can swelling.

Given Data / Assumptions:

• Product class: medium-acid (pH 5.3–4.5).
• Potential spoilage types: flat-sour, putrefaction, TA spoilage.
• We seek the most likely phenomenon for this pH band.

Concept / Approach:
Flat-sour spoilage is characterized by acid production without gas formation, often due to Bacillus coagulans or related thermophiles in acid and medium-acid foods. Putrefaction (protein breakdown with gas and foul odor) dominates low-acid, protein-rich matrices. TA spoilage classically refers to thermophilic anaerobes producing gas in low-acid canned foods.

Step-by-Step Solution:
Match pH band (5.3–4.5) to typical spoilers: thermophilic aciduric Bacillus are prime suspects.Identify the expected defect: non-gassy, sour spoilage (flat-sour).Eliminate gas-forming putrefaction and TA as less consistent with this pH category.

Verification / Alternative check:
Historical surveys of canned tomato products and similar matrices repeatedly document flat-sour as the predominant defect under marginal processes.

Why Other Options Are Wrong:
Putrefaction is more common in low-acid, proteinaceous canned foods; TA spoilage is a low-acid gas defect; “both” overgeneralizes.

Common Pitfalls:
Expecting can swelling with all spoilage; many flat-sour cans remain flat and are detected only by off-flavor and pH drop.

Final Answer:
Flat-sour spoilage.