Pasteurised milk is most commonly tested by

Phosphatase test:This is a check on whether milk has been pasteurized. The enzyme phosphatase, which is normally present in milk, is inactivated if pasteurization has been performed properly. Residual phosphatase activity indicates that pasteurization has been adequate. This test, if positive after proper pasteurization of milk shows contamination after pasteurization. (Ref: Ananthanarayan 9th edition, p631-632)