Question:
Presence of which of the following bacteria in sterilized evaporated milk causes, a non-acid curd that develops into a brownish liquid with a bitter taste.
Presence of which of the following bacteria in sterilized evaporated milk causes, a non-acid curd that develops into a brownish liquid with a bitter taste.
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"Sweet curdling followed by liquefaction and bitterness" is a classic sign of proteolysis caused by spore-forming *Bacillus* species, particularly *Bacillus subtilis* or *Bacillus cereus*.
Updated On: Jul 21, 2026
- B. megaterium
- Geobacillus stearothermophilus
- Candida spp.
- B. subtilis
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Verified By Collegedunia
The Correct Option is D
Solution and Explanation
Step 1: Understanding the Concept:
Sterilized evaporated milk can undergo bacterial spoilage if spore-forming bacteria survive the heat sterilization process or enter through container leaks.
Detailed Explanation:
Some species of the genus Bacillus produce highly heat-resistant endospores that can survive commercial sterilization.
Let us analyze how these different species affect evaporated milk:
- Bacillus subtilis: This bacterium produces active extracellular proteolytic enzymes (proteases).
These enzymes cause "sweet curdling" (clotting of milk without acid production) by acting similarly to rennet.
Over time, these proteases break down the milk proteins into peptides and amino acids, liquefying the curd into a brownish liquid and producing a bitter taste due to the accumulation of hydrophobic peptides.
This matches the description given in the question.
- Bacillus megaterium: Can cause coagulation, but typically produces different physical defects, often accompanied by gas.
- Geobacillus stearothermophilus: This thermophilic spore-former causes "flat sour" spoilage, characterized by acid production without gas, but does not produce the characteristic liquefied bitter brown defect.
- Candida species: Non-spore-forming yeasts that are easily destroyed by pasteurization and cannot survive sterilization.
Step 2: Final Answer:
The bacterium responsible for this defect is Bacillus subtilis.
Sterilized evaporated milk can undergo bacterial spoilage if spore-forming bacteria survive the heat sterilization process or enter through container leaks.
Detailed Explanation:
Some species of the genus Bacillus produce highly heat-resistant endospores that can survive commercial sterilization.
Let us analyze how these different species affect evaporated milk:
- Bacillus subtilis: This bacterium produces active extracellular proteolytic enzymes (proteases).
These enzymes cause "sweet curdling" (clotting of milk without acid production) by acting similarly to rennet.
Over time, these proteases break down the milk proteins into peptides and amino acids, liquefying the curd into a brownish liquid and producing a bitter taste due to the accumulation of hydrophobic peptides.
This matches the description given in the question.
- Bacillus megaterium: Can cause coagulation, but typically produces different physical defects, often accompanied by gas.
- Geobacillus stearothermophilus: This thermophilic spore-former causes "flat sour" spoilage, characterized by acid production without gas, but does not produce the characteristic liquefied bitter brown defect.
- Candida species: Non-spore-forming yeasts that are easily destroyed by pasteurization and cannot survive sterilization.
Step 2: Final Answer:
The bacterium responsible for this defect is Bacillus subtilis.
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