Milk protein is used commercially in

Options

A. Sizing for coating paper
B. Glues
C. Cosmetics
D. All the above

Answer

### Step-by-Step Solution:

1. **Identify the Milk Protein**: The primary protein found in milk is known as casein. It is a significant source of nutrition and plays a vital role in various metabolic processes in the human body.

2. **Understand the Properties of Casein**: Casein is classified as a natural polymer. Natural polymers are large molecules made up of repeating structural units, and casein can be modified through various methods.

3. **Explore Commercial Uses**: Casein can be modified chemically, enzymatically, or through physical means (like heat). This versatility allows it to be used in various commercial applications.

4. **List the Applications**: The commercial uses of casein include:
- **Sizing for Coating Paper**: Casein is used to improve the quality and durability of paper.
- **Glues**: Due to its adhesive properties, casein is utilized in the production of various types of glues.
- **Cosmetics**: It is also found in some cosmetic products due to its beneficial properties for skin.

5. **Conclude with the Correct Answer**: Since casein is used in all the mentioned applications (sizing for coating paper, glues, and cosmetics), the correct answer to the question is "all of the above."

### Final Answer:
Milk protein (casein) is used commercially in sizing for coating paper, glues, cosmetics, and all of the above.

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