Question

Non acid coagulation defect in Evaporated milk is caused by

• A. Bacillus cereus
• B. Bacillus coagulans
• C. Geo-bacillus stearothermophilus
• D. Bacillus subtilis

Hint:

Remember: Coagulation without souring (acid) is caused by proteolytic enzymes. Bacillus subtilis is highly proteolytic and causes non-acid coagulation, whereas Bacillus coagulans causes acid coagulation (flat sour).

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
"Non-acid coagulation" (also termed sweet curdling) refers to the coagulation of milk proteins at a near-neutral pH without significant lactic acid production.
This defect is caused by extracellular, rennet-like proteolytic enzymes secreted by surviving bacterial spores.

Step 2: Detailed Explanation:
Evaporated milk undergoes retort sterilization, which destroys vegetative cells but may allow extremely heat-resistant bacterial endospores to survive.
- Bacillus coagulans is a thermo-acidurics spore-former that ferments sugar to produce lactic acid, causing "flat sour" spoilage (acid coagulation).
- Geobacillus stearothermophilus is a thermophile that causes flat sour spoilage at high storage temperatures without gas.
- {Bacillus subtilis is a mesophilic spore-former capable of surviving moderate retort processes.
During storage, B. subtilis spores germinate and produce large amounts of extracellular proteases (specifically metalloproteases).
These proteases mimic the action of chymosin (rennet) by selectively cleaving the Phe\(_{105}\)-Met\(_{106}\) peptide bond of \(\kappa\)-casein.
This destabilizes the casein micelle system, causing them to aggregate and form a firm, gelled coagulum.
Because this enzymatic cleavage occurs without carbohydrate fermentation, the pH of the milk remains relatively unchanged, resulting in a non-acid coagulation defect.

Step 3: Final Answer:
The non-acid coagulation defect in evaporated milk is primarily caused by Bacillus subtilis.