Explanation:

Starch or amylum is a polymeric carbohydrate consisting of numerous glucose units joined by glycosidic bonds. This polysaccharide is produced by most green plants as energy storage. It is the most common carbohydrate in human diets and is contained in large amounts in staple foods like potatoes, wheat, maize (corn), rice, and cassava. Pure starch is a white, tasteless and odorless powder that is insoluble in cold water or alcohol.
Rennin play an important role in helping young mammals to digest milk. Rennin, protein-digesting enzyme that curdles milk by transforming caseinogen into insoluble casein; it is found only in the fourth stomach of cud-chewing animals, such as cows. Its action extends the period in which milk is retained in the stomach of the young animal.
Lactobacillus bacteria cause for milk spoil. Milk spoils when bacteria converts the lactose into glucose and galactose, producing lactic acid. Lactic acid creates casein and then forms a curd that can quickly curdle the milk within 24 hours.