Question:
Information on heat classification of milk powder CANNOT be obtained using which of the following indices?
Information on heat classification of milk powder CANNOT be obtained using which of the following indices?
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WPNI, casein number, and cysteine reactions are all based on protein denaturation and structural changes, whereas urea is a heat-stable non-protein nitrogen molecule that is unaffected by thermal processing.
Updated On: Aug 7, 2026
- Whey protein nitrogen index
- Cysteine number
- Casein number
- Urea number
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Verified By Collegedunia
The Correct Option is D
Solution and Explanation
Step 1: Understanding the Concept:
Heat classification of skim milk powder is based on measuring the degree of thermal denaturation of milk proteins, particularly the heat-sensitive whey proteins.
Step 2: Detailed Explanation:
Let us evaluate the relevance of each index to thermal denaturation:
1. Whey protein nitrogen index (WPNI): This is the standard industrial index, which measures the concentration of undenatured whey protein nitrogen remaining in the powder.
2. Cysteine number: Whey proteins (primarily \(\beta\)-lactoglobulin and bovine serum albumin) contain cysteine residues with sulfhydryl groups and disulfide bonds.
Heating induces sulfhydryl-disulfide exchange and oxidation reactions.
Measuring changes in free cysteine or sulfhydryl group concentrations can serve as an indicator of thermal treatment.
3. Casein number: This measures the percentage of total nitrogen that is casein nitrogen.
Denatured whey proteins co-precipitate with casein during acid precipitation, which alters the measured casein number.
4. Urea number: Urea is a small, heat-stable, non-protein nitrogen (NPN) molecule present in milk.
Its concentration is influenced by maternal diet and metabolism rather than thermal processing, and it is not altered by standard milk powder heat treatments.
Therefore, the urea number cannot be used for heat classification.
Step 3: Final Answer:
Therefore, information on heat classification of milk powder cannot be obtained using the urea number.
Heat classification of skim milk powder is based on measuring the degree of thermal denaturation of milk proteins, particularly the heat-sensitive whey proteins.
Step 2: Detailed Explanation:
Let us evaluate the relevance of each index to thermal denaturation:
1. Whey protein nitrogen index (WPNI): This is the standard industrial index, which measures the concentration of undenatured whey protein nitrogen remaining in the powder.
2. Cysteine number: Whey proteins (primarily \(\beta\)-lactoglobulin and bovine serum albumin) contain cysteine residues with sulfhydryl groups and disulfide bonds.
Heating induces sulfhydryl-disulfide exchange and oxidation reactions.
Measuring changes in free cysteine or sulfhydryl group concentrations can serve as an indicator of thermal treatment.
3. Casein number: This measures the percentage of total nitrogen that is casein nitrogen.
Denatured whey proteins co-precipitate with casein during acid precipitation, which alters the measured casein number.
4. Urea number: Urea is a small, heat-stable, non-protein nitrogen (NPN) molecule present in milk.
Its concentration is influenced by maternal diet and metabolism rather than thermal processing, and it is not altered by standard milk powder heat treatments.
Therefore, the urea number cannot be used for heat classification.
Step 3: Final Answer:
Therefore, information on heat classification of milk powder cannot be obtained using the urea number.
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