Which of the following are non - reducing sugars ?

Options

A. Sucrose
B. Stachyose
C. Lactose
D. (1) & (2)

Answer

To determine which of the following are non-reducing sugars, we need to analyze the options provided: sucrose, stachyose, lactose, and the combination of sucrose and stachyose.

### Step-by-Step Solution:

1. **Understand Non-Reducing Sugars**:
Non-reducing sugars do not have a free aldehyde or ketone group that can be oxidized. This is typically due to the presence of glycosidic bonds that involve the anomeric carbon of the sugar, preventing it from participating in redox reactions.

2. **Identify the Options**:
The options given are:
- Option 1: Sucrose
- Option 2: Stachyose
- Option 3: Lactose
- Option 4: First and second (sucrose and stachyose)

3. **Analyze Sucrose**:
- Sucrose is a disaccharide composed of glucose and fructose.
- In sucrose, both anomeric carbons are involved in the glycosidic bond, meaning there are no free hydroxyl (OH) groups available for oxidation.
- Therefore, sucrose is a non-reducing sugar.

4. **Analyze Stachyose**:
- Stachyose is an oligosaccharide made up of two galactose units, one glucose unit, and one fructose unit.
- Similar to sucrose, stachyose has multiple anomeric carbons involved in glycosidic bonds, which means it also lacks free OH groups.
- Hence, stachyose is also a non-reducing sugar.

5. **Analyze Lactose**:
- Lactose is a disaccharide composed of glucose and galactose.
- In lactose, there is a free anomeric carbon that has a hydroxyl group, allowing it to participate in redox reactions.
- Thus, lactose is a reducing sugar.

6. **Conclusion**:
- Based on the analysis, the non-reducing sugars among the options are sucrose and stachyose.
- Therefore, the correct answer is option 4: first and second (sucrose and stachyose).

### Final Answer:
The non-reducing sugars are **option 4: first and second (sucrose and stachyose)**.