Which microorganism improves the nutritional quality of curd by increasing vitamin `B_(12)` ?

Answer

**Step-by-Step Solution:**

1. **Understanding the Composition of Milk**: Milk contains lactose, which is a sugar that serves as a substrate for fermentation.

2. **Role of Lactic Acid Bacteria**: When milk is fermented, lactic acid bacteria (LAB) act on lactose. These bacteria are responsible for the fermentation process that leads to the formation of curd.

3. **Fermentation Process**: During fermentation, lactic acid is produced, which lowers the pH of the milk. This decrease in pH causes the protein casein in milk to coagulate.

4. **Formation of Curd**: The coagulation of casein results in the formation of curd. This process is known as lactic acid fermentation.

5. **Nutritional Enhancement**: Lactic acid bacteria not only help in curd formation but also enhance the nutritional quality of the curd by increasing the levels of vitamin B12.

6. **Conclusion**: The microorganism that improves the nutritional quality of curd by increasing vitamin B12 is lactic acid bacteria.

**Final Answer**: Lactic acid bacteria.

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