Question:
Which of the following bacterial metabolites are responsible for "fruity" off-flavor in raw milk?
Which of the following bacterial metabolites are responsible for "fruity" off-flavor in raw milk?
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In dairy chemistry, "fruity" off-flavors are always caused by volatile esters (like ethyl butyrate) produced through the activity of psychrotrophic bacteria.
Updated On: Jul 8, 2026
- Acetic acid
- Diacetyl
- Ethanol
- Ethyl butyrate
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The Correct Option is D
Solution and Explanation
Step 1: Understanding the Concept:
The growth of psychrotrophic bacteria in cold-stored raw milk can lead to the production of volatile organic compounds that cause distinct flavor defects.
Step 2: Detailed Explanation:
- Psychrotrophic bacteria, particularly Pseudomonas fragi, produce esterase enzymes that catalyze the esterification of milk fatty acids with ethanol.
- This reaction produces volatile esters, such as ethyl butyrate and ethyl hexanoate.
- These esters are highly aromatic and responsible for the distinct, sweet, "fruity" off-flavor (resembling apples or strawberries) in spoiled raw milk.
- Acetic acid causes a sour/vinegary flavor, diacetyl provides a buttery aroma, and ethanol produces an alcoholic flavor.
Step 3: Final Answer
The metabolite responsible for the fruity off-flavor in raw milk is ethyl butyrate.
The growth of psychrotrophic bacteria in cold-stored raw milk can lead to the production of volatile organic compounds that cause distinct flavor defects.
Step 2: Detailed Explanation:
- Psychrotrophic bacteria, particularly Pseudomonas fragi, produce esterase enzymes that catalyze the esterification of milk fatty acids with ethanol.
- This reaction produces volatile esters, such as ethyl butyrate and ethyl hexanoate.
- These esters are highly aromatic and responsible for the distinct, sweet, "fruity" off-flavor (resembling apples or strawberries) in spoiled raw milk.
- Acetic acid causes a sour/vinegary flavor, diacetyl provides a buttery aroma, and ethanol produces an alcoholic flavor.
Step 3: Final Answer
The metabolite responsible for the fruity off-flavor in raw milk is ethyl butyrate.
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