Answer 1

Lactobacillus and other Lactic Acid Bacteria (LAB) are responsible for the curdling of milk. These bacteria utilize and act upon the milk sugar lactose leading to its oxidation to lactic acid. This lactic acid produced in turn leads to partial digestion and coagulation of milk proteins to form the curd. Action by LAB also leads to an increase in vitamin B₁₂ content of the curd.

On consumption of curd, these bacteria add to the healthy and beneficial gut flora outcompeting the growth of harmful gut flora.