Question

Which of the following organisms is most likely to cause lipolysis in milk?

• A. Staphylococcus aureus
• B. Bacillus cereus
• C. Pseudomonas
• D. Clostridium

Hint:

Psychrotrophic Pseudomonas species are the primary source of heat-stable lipases and proteases, making them the leading cause of rancidity (lipolysis) and bitterness (proteolysis) in stored dairy products.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Lipolysis in milk is the enzymatic hydrolysis of milk fat (triglycerides) into free fatty acids and glycerol, which can cause rancid off-flavors.

Step 2: Detailed Explanation:
- Psychrotrophic bacteria, particularly species of the genus Pseudomonas (such as Pseudomonas fluorescens), produce highly active, heat-stable extracellular lipases during cold storage.
- While the pasteurization process easily kills the vegetative cells of Pseudomonas, their extracellular lipolytic enzymes survive pasteurization and continue to break down milk fats during subsequent storage.
- This enzymatic activity leads to the accumulation of short-chain free fatty acids, imparting a rancid, soapy, or bitter flavor to the milk.
- Other options like S. aureus, B. cereus, and Clostridium are less associated with psychrotrophic lipolytic spoilage in fluid milk.

Step 3: Final Answer
The organism most commonly associated with causing lipolysis in refrigerated milk is Pseudomonas.