Question

Which one is not used in the production of Yoghurt?
A. Streptococcus lactis
B. Streptococcus thermophilus
C. Lactobacillus bulgaricus
D. Acetobacter aceti

Answer 1

Hint: The bacterial fermentation of milk results in the production of Yoghurt. The cow’s milk is most commonly used to make Yoghurt. The yoghurt is produced by using bacteria.

Complete Answer:
- The bacteria used to make yoghurt are called yoghurt cultures.
- The fermentation of lactose is done by these bacteria.
- The fermentation results in production of lactic acid, which acts on milk protein to give yoghurt.
- It is produced by using a culture of bacteria. The lactobacillus and streptococcus species are used.
- The lactose is the sugar present in milk and it is fermented to lactic acid.
- The acid helps in restricting the growth of food poisoning bacteria.
- The yoghurt is produced by denaturing the proteins of milk and then cooling it to temperature so that the live microorganisms would not be killed because they turn milk into yoghurt.

The yoghurt is made by:
- Collect milk
- Pasteurise the milk at $80^\circ$C - $85^\circ$C for 15-20 minutes.
- Cool the milk at $40^\circ$C - $45^\circ$C.
- Add culture to the bacteria.
- Now keep the milk for 3-4 hours. The fermentation is taking place. The long fermentation time produces more acidic yoghurt.
- Cool the yoghurt in the refrigerator.
- So the yoghurt is produced from the streptococcus lactis, streptococcus thermophilus and lactobacillus bulgaricus.

So the correct answer is Acetobacter aceti.

Note: Yoghurt is good for bones. It controls blood pressure. Yoghurt improves immunity. The main problems in yoghurt making –spoil by bacteria, maintenance of correct incubation and correct balance of lactobacillus bacteria is important for good yoghurt. The Acetobacter aceti is used in the production of vinegar.