in which u03b2 casein is largely soluble whereas at least some contaminants remain insoluble in accordance with the present invention it has been found that a large variety of standard buffer systems may be employed in which the ph is maintained between about 7 5 and 9 8 preferably between 8 2 and 9 0 most preferably about 8 5 with the initial ph adjusted as needed by the addition of acid e g hcl or base e g naoh in addition it has been found that the inclusion of a protein solubilizing agent such as urea or guanidine hcl significantly enhances the solubility of u03b2 casein in buffers at higher ph and therefore such an agent is included in the second solutions of the invention thus for example the buffer system may comprise tris in an aqueous solution at a concentration of between about 20 mm and 60 mm preferably about 50 mm and urea at a concentration of between about 2 5 m and 8 0 m preferably between 3 0 m and 7 0 m most preferably about 6 m with the initial ph adjusted as needed by the addition of acid e g hcl or base e g naoh alternative buffer system include guanidine buffers e g 4 6 m and ethanolamine buffers e g 30 60 mm all of which are well known in the art the ethanolamine buffer system would require the use of a protein solubilizing agent preferably urea in addition the second solution.