In the case of milk quality, what is the purpose pasteurization? And how could check that milk will be adequate pasteurization?

Pasteurisation is an essential process in the production of milk which is safe and free from pathogens. Alkaline Phosphatase is an enzyme which is naturally present in milk, but is destroyed at a temperature just near to the pasteurization temperature. Alkaline Phosphatase test is used to indicate whether milk has been adequately pasteurised or whether it has been contaminated with raw milk after pasteurisation. This test is based on the principle that the alkaline phosphatase enzyme in raw milk liberates phenol from a disodium para-nitro phenyl phosphate and forms a yellow coloured complex at alkaline pH (Scharer, 1943). The intensity of yellow colour produced is proportional to the activity of the enzyme. The colour intensity is measured by direct comparison with standard colour discs in a Lovibond comparator. The test is not applicable to sour milk and milk preserved with chemical preservatives.