Question

Which of the following is NOT responsible for cooked flavour in case of heated milk?

• A. Butyric acid
• B. Sulphur compounds
• C. Lactones
• D. Methyl ketones

Hint:

The "cooked flavor" of pasteurized or UHT milk is primarily driven by volatile sulfur compounds (from denatured whey proteins), methyl ketones, and lactones (from milk fat).
Butyric acid causes offensive, rancid defects.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Subjecting milk to high-temperature thermal treatments (such as pasteurization, sterilization, or ultra-pasteurization) induces chemical changes that generate volatile flavor compounds.
These compounds collectively contribute to the characteristic "cooked," "heated," or "rich" caramelized flavor profile of processed milk.

Step 2: Detailed Explanation:
Let us evaluate the contributions of the listed compounds to the flavor profile of heated milk:
1. Sulphur compounds (B): These are the primary compounds responsible for the distinct "cooked" or "cabbagy" notes in freshly heated milk.
Heating denatures whey proteins, specifically \(\beta\)-lactoglobulin and proteins of the fat globule membrane, exposing and thermally decomposing their sulfhydryl (-SH) groups to release volatile sulfur compounds like hydrogen sulfide (\(\text{H}_2\text{S}\)) and dimethyl sulfide.
2. Methyl ketones (D): These volatile compounds are formed during heating via the non-oxidative decarboxylation of free saturated fatty acids or the thermal breakdown of glycerides.
They contribute a pleasant, rich, and slightly heated flavor note to sterilized milk.
3. Lactones (C): Volatile \(\delta\)- and \(\gamma\)-lactones are cyclic esters formed by the monohydrolytic cyclization of hydroxy fatty acids during heating.
They impart a sweet, peach-like, or buttery flavor, contributing to the typical heated milk aroma.
4. Butyric acid (A): This short-chain fatty acid is released via the enzymatic or chemical hydrolysis of milk fat (hydrolytic rancidity).
It produces a pungent, sweaty, rancid, and offensive odor, which is a recognized quality defect and does not contribute to the desirable cooked flavor profile.

Step 3: Final Answer:
Butyric acid is associated with hydrolytic rancidity and is not responsible for the cooked flavor of heated milk.