Fifteen mL of Low fat cow's milk sample was first defatted by centrifugation at 3000 rpm for 10 min at 4 °C. Then 1 mol L−1 HCl solution was added to the sample of the resulting defatted milk to adjust the pH to 4.6. After incubation for 30 min at room temperature, the sample was again centrifuged at 4000 rpm for 30 min at 4 °C. Then the clear solution from the top was separated and transferred into a volumetric flask.