During the production of curd, a small amount of curd is added as a starter to the fresh milk at a suitable temperature.Explain the changes the milk undergoes when it sets into curd

(i) When a small amount of curd is added as a starter to the fresher milk at a suitable temperature, a micro-organism Lactobacillus and lactic acid bacteria grows in milk in millions and convert milk into curd.
(ii)Micro-organism increases its nutritional quality increasing vitamin ${{B}_{12}}$