Question

Choose the microorganisms that are involved in yoghurt production:
(i) Streptococcus thermophilus
(ii) Lactobacillus bulgaricus
(iii) E.coli
(iv) Vibrio

Answer 1

Hint: Yogurt is a dairy product made from the fermentation of milk by bacteria. Yogurt cultures are the bacteria that are used to manufacture yoghurt. These bacteria make lactic acid by fermenting carbohydrates in milk, which reacts with milk protein to give yoghurt its texture and acidic flavour. The most frequent milk used to produce yoghurt is cow's milk. Yogurt is also made from the milk of water buffalo, goats, ewes, mares, camels, yaks, and plant milks.

Complete answer:
(i) Streptococcus thermophilus and (ii) Lactobacillus bulgaricus are the correct choices.
These are the microorganisms that are used to make yoghurt. These are the bacteria responsible for converting lactose sugar in milk to lactic acid. Lactic acid is what turns milk into yoghurt.
Lactic acid is created as a byproduct of bacterial fermentation of milk, which produces yoghurt. Lactobacillus bulgaricus and Streptococcus thermophilus coagulate the milk protein and convert the lactose in the milk to lactic acid. Acetaldehyde is responsible for the flavour of yoghurt.

Streptococcus thermophilus is a Gram-positive, nonmotile, spherical to ovoid coccus with a diameter of 0.7–0.9 m that occurs in pairs and chains, some of which can be quite lengthy. The bacterium grows best between 40–45 °C, with a minimum of 20–25 °C and a high of near 47–50 °C.

Lactobacillus bulgaricus and Streptococcus thermophilus are the main (starter) microorganisms in yoghurt. The starter cultures are responsible for fermenting lactose (milk sugar) into lactic acid. Lactic acid increases the pH of the milk, causing it to coagulate or form the soft gel that is characteristic of yoghurt.

Note:
Curd, also known as dahi, is a dairy product made by curdling milk with an acidic material such as lemon juice, vinegar, or even curd itself. Yogurt, on the other hand, is made from milk that has been fermented by microorganisms. Yogurt is made with a yoghurt culture that includes Lactobacillus bulgaricus and Streptococcus thermophilus.