Question

Curdling of milk takes place by
A. Streptococcus locus
B. Streptococcus thermophilus
C. Lactobacillus or Lactococcus lactis
D. All of the above

Answer 1

Hint: Curdling is the break down of an emulsion or colloid into large parts of various components through the physico-chemical methods of flocculation, creaming, and coalescence. Curdling is the process that is used in making cheese and tofu, sauce, and custard.

Complete answer:
Curdled milk is formed when a small lump is formed in the milk. The pH is of milk slightly acidic. When the pH is reduced even more by the addition of another acidic component, the protein molecules cease to repel each other. This repulsion allows the proteins to stick together or coagulate into the clumps known as curds. Curd has the Lactobacillus bacteria in it. Lactobacillus bacteria then convert the sugar (lactose) into an acid (lactic acid) by the process of fermentation. When milk is heated to a high temperature and a small amount of old curd is added to it, the Lactobacillus in that curd starts to multiply. This bacteria converts the lactose into lactic acid, which gives the sour taste to curd as the optimum temperature is obtained, at this temperature the bacteria grow luxuriously and changes the pH of the milk.
Hence, the correct answer is option C.
Additional Information:-
Lactobacillus are homofermentative i.e. the hexoses are metabolized by glycolysis to lactate as the major end product. Lactobacillus are good for gut health. They produce lactic acid, which prevents harmful bacteria from growing in the intestine. It also reduces high cholesterol levels which increases the risk for heart disease. It also prevents and reduces diarrhoea, it also improves bowel movements. It also reduces and prevents vaginal infection in females.

Note: Curdling of milk also occurs when the milk is too old. This type of old milk should not be consumed and should be thrown out. It can cause severe health issues. Curdling also requires a high temperature, it doesn't show Curdling when it is kept at a low temperature in the refrigerators.