Food microbiology — bakery spoilage: In commercial bread, the defect called “ropiness” (sticky, stringy crumb with fruity odour) is typically caused by which microorganism?

Introduction / Context:
Ropiness in bread is a classic spoilage problem in baking and food microbiology. It presents as a sticky, stringy crumb and an unpleasant sweet or fruity odour, often noticed after slicing. Identifying the responsible organisms helps bakers select appropriate control steps such as sanitation, cooling practices, and the use of preservatives.

Given Data / Assumptions:

• The question asks for the primary causative agent of rope spoilage in bread.
• Candidate organisms include bacteria and molds commonly encountered in bakery environments.
• Assume standard bread made from wheat flour, baked and then cooled/stored at ambient conditions.

Concept / Approach:
Rope spoilage is chiefly bacterial, not fungal. The main agents are Bacillus species (historically Bacillus subtilis and Bacillus licheniformis). Their spores survive baking and can germinate in warm, moist bread during slow cooling or improper storage. They produce extracellular enzymes that degrade starches and proteins, causing the characteristic sticky strands and off-odours.

Step-by-Step Solution:
Link the named defect “ropiness” specifically with Bacillus spp. (rope-forming bacteria). Recall that Bacillus spores can withstand baking and later germinate in the loaf. Recognize that common bakery molds (Aspergillus, Rhizopus, Penicillium) cause visible mold growth, not the rope phenotype. Select the organism classically associated with rope: Bacillus subtilis.

Verification / Alternative check:
Quality manuals note rope occurrence increases with warm weather, slow cooling, and high loaf moisture. Acidification (e.g., sourdough), use of approved preservatives (such as propionates), rapid cooling, and strict sanitation reduce the risk.

Why Other Options Are Wrong:

• Aspergillus niger / Rhizopus nigricans / Penicillium expansum: These molds typically cause surface mold growth and visible colonies rather than rope; they are not the hallmark rope agents.
• Candida albicans: A yeast associated with clinical settings; not the classic bread rope organism.

Common Pitfalls:
Confusing any post-bake spoilage with mold growth; rope is a bacterial spoilage with a distinctive stringy crumb and fruity odour, not fuzzy mold.

Final Answer:
Bacillus subtilis is the typical cause of ropiness in bread.