Question

Unclean flavor production in milk arises from
A. Dimethyl sulfide
B. Gram -ve psychrotrophic rods
C. Hydrogen Sulphide
D. Gram +ve cocci
Choose the correct answer from the options given below:

• A. A and B only
• B. B and C only
• C. C and D only
• D. A and D only

Hint:

Gram-negative psychrotrophic rods (e.g., Pseudomonas) are the most common cause of lipolytic and proteolytic off-flavors in refrigerated milk.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Unclean flavor is a sensory defect in milk characterized by a stale, unpleasant, or sewer-like odor and taste.
It is primarily caused by biochemical activities of bacterial contaminants during cold storage, which release volatile compounds.

Step 2: Detailed Explanation:
Let us analyze the contributors to unclean flavors:
- A. Dimethyl sulfide (DMS): At very low levels, DMS can contribute to a normal cowy or feed-like flavor.
However, elevated concentrations produced by bacterial fermentation result in an objectionable, unclean, or malty off-flavor. (True)
- B. Gram -ve psychrotrophic rods: Members of this group, such as Pseudomonas, Coliforms, and Achromobacter, grow at refrigeration temperatures.
They produce active lipolytic and proteolytic enzymes that break down milk proteins and lipids, releasing foul-smelling compounds that cause a distinct unclean flavor. (True)
- C. Hydrogen Sulphide: While this gas imparts a rotten-egg odor, it is associated with extreme spoilage or chemical degradation, rather than the specific common "unclean" sensory classification. (False)
- D. Gram +ve cocci: These organisms (like micrococci or streptococci) are less active at cold temperatures and generally produce clean acid flavors rather than psychrotrophic unclean defects. (False)
Thus, the primary causes of unclean flavor are dimethyl sulfide and Gram-negative psychrotrophic rods.

Step 3: Final Answer
The correct option is (A).