Q. Evaluate precentage Proteins in Milk ?
Milk comprises of casein, lactoalbumins and lactoglobulins. About 82 per cent of the protein in milk is casein and the remaining proteins are whey proteins, which are lactoalbumin and lactoglobulin. Casein binds with calcium in milk and forms the calcium-caseinate complex, which is present in the colloidal form. Acid, rennet, alcohol and heat can precipitate this complex.
The proteins in milk are determined by the Kjeldahl procedure, which is defined as the amount of nitrogen experimentally found and multiplied by an approximate conversion factor. In this procedure, as you may have already studied about in the Nutritional Biochemistry practical, the sample of milk is oxidized in the presence of sulphuric acid and nitrogenous compounds are converted into ammonium sulphate. Ammonia is liberated by adding an excess of alkali and is quantitatively distilled into a measured volume of standard hydrochloric acid or sulphuric acid. The acid not neutralized by ammonia is back-titrated with standard alkali.