Question

Coagulation of evaporated milk accompanied by gas and cheesy odour is carried by

• A. Bacillus cereus
• B. Bacillus subtilis
• C. Bacillus panis
• D. Bacillus megaterium

Hint:

Remember the classic signatures of spore spoilage in canned milk:
- B. coagulans = Acid curdling (Flat sour, no gas).
- B. subtilis = Proteolytic curdling + Gas + Cheesy odour.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Evaporated milk is a sterilized, concentrated dairy product.
Spoilage is typically caused by highly heat-resistant bacterial endospores that survive the retort sterilization process or enter via post-processing can-seaming leaks.

Step 2: Detailed Explanation:
Various spore-forming Bacillus species are responsible for distinct spoilage syndromes in canned evaporated milk:
- Bacillus coagulans (formerly sometimes linked to Bacillus panis) is the classic cause of "flat sour" spoilage, where it produces acid and coagulates milk without producing gas.
- Bacillus cereus is typically associated with "sweet curdling" (coagulation with minimal acid production) in pasteurized milk but is less common in severe retort-sterilized products.
- {Bacillus subtilis is unique in its ability to produce highly active extracellular proteases along with amylolytic activity that can yield gaseous byproducts under specific conditions inside canned milk.
When B. subtilis spoils evaporated milk, it aggressively degrades caseins into bitter peptides and volatile compounds, giving rise to a distinct, pungent cheesy odour.
This proteolysis is accompanied by gas generation (often from the breakdown of nitrogenous compounds or trace fermentation), causing bloating of the can and complete coagulation of the milk.

Step 3: Final Answer:
The coagulation of evaporated milk characterized by gas accumulation and a cheesy odor is caused by Bacillus subtilis.