The lactic acid bacteria Streptococcus thermophilus and Lactobacillus bulgaricus converts

Options

A. Lactose in lactic acid
B. Lactic acid into lactose sugar
C. Casein into lactic acid
D. None of these

Answer

**Step-by-Step Solution:**

1. **Identify the Bacteria**: The question mentions two specific lactic acid bacteria: *Streptococcus thermophilus* and *Lactobacillus bulgaricus*.

2. **Understand the Role of These Bacteria**: These bacteria are primarily known for their role in the fermentation process, particularly in yogurt production.

3. **Recognize the Substrate**: The primary substrate that these bacteria act upon is lactose, which is the sugar found in milk.

4. **Describe the Conversion Process**: The bacteria convert lactose into lactic acid through fermentation. This process is crucial for the thickening of milk into yogurt.

5. **Explain the Resulting Product**: As lactic acid is produced, it lowers the pH of the milk, causing it to coagulate and form a soft gel, which is the texture of yogurt.

6. **Conclude the Answer**: Therefore, the correct conversion that occurs is from lactose to lactic acid.

**Final Answer**: The lactic acid bacteria *Streptococcus thermophilus* and *Lactobacillus bulgaricus* convert lactose to lactic acid.

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