迫 Experimental principle 1. Casein is a kind of complex phosphoprotein, and due to its nature of being amphoteric compound, the acid-base property of the solution will obviously affect the charge on protein. When the ph of milk adjusted close to the pl of casein (pl=4.8), the protein becomes neutral. Since its lowest solubility, sediment will form, which could be separated through centrifugation NH NH2 H salt high solubility low solubility salt( high solubility)●1.Casein is a kind of complex phosphoprotein, and due to its nature of being amphoteric compound, the acid-base property of the solution will obviously affect the charge on protein. When the pH of milk adjusted close to the pI of casein (pI=4.8), the protein becomes neutral. Since its lowest solubility, sediment will form, which could be separated through centrifugation. salt （ high solubility ） low solubility salt （ high solubility ） Experimental principle