Characterization of Casein Synthesized by Protonation with organic and inorganic acids

Casein is the dominant protein in cow’s milk .The pH value of milk is 6.6 where casein has a negative charge to prevent its coagulation.By gaining protons, casein reaches to its isoelectric point (pH 4.6) where it coagulates to produce a solid precipitate.The casein was prepared by reducing the pH introducing organic and inorganic acids to heated skim milk. As organic acids, acetic, lactic, formic and ascorbic were used and H₃PO₄, H₂SO₄ and HNO₃ were used as the inorganic acids. The casein obtained with different acids was washed and dried. A paste was made by ball milling aforementioned casein with distilled water. This paste was used to cast thin films on conducting glass by doctor blade method.The films were characterized with the Mott-Schottky measurements(MS) and UV-Visible spectroscopy. Significance difference could not be seen with the above measurements depending on the acid used to prepare casein. The MS analysis revealed that casein has n-type conductivity where its conduction band lies at - 0.61V with respect to the Ag/AgCl electrode. Band gap of casein found to be 3.9 eV that calculated from tauc plot .The results indicated that casein is a good insulating material, but further studies are ongoing to tune its conductivity for applications in optoelectronic devices.