Physical characterizations of casein by using electrochemical and spectroscopic techniques

Casein is the major protein present in cow’s milk. Lowering the pH of cow’s milk by addition of acids, natural casein can be precipitated, which can be utilized in fabricating thin film of polymer matrix for electrodes of optoelectronic devices. In the current study, casein was isolated by using several organic and inorganic acids. As organic acids, acetic, lactic, formic and ascorbic acids were used and H3PO4, H2SO4 and HNO3 were used as the inorganic acids. Thin films of casein were deposited on conducting tin oxide glass plates by using the casein precipitated with each acid and electrochemically characterized. But any significant difference could not be seen in the above measurements, where the same yield and results were obtained with all acids. Therefore, in further studies, casein isolated from acetic acid was used because of the safeness in using diluted acetic acid solution. These casein films were physically characterized by using impedance and optical spectroscopic techniques. Mott-Schottky analysis has shown that casein is having an n-type conductivity with flat band potential at - 0.61V. The impedance spectroscopic analysis was used to calculate the electrical conductivity and dielectric constant of casein which were found to be 1.13×10-2 mS/m and 6.6 respectively. The band gap of synthesized casein was determined by drawing tauc plot using the UV visible spectroscopic data which was found to be 3.9 eV. Fourier transform infrared spectra of casein sample were recoded to confirm the presence of functional groups in the synthesized compound. With this characterization, it was evident that casein is a prospective material to fabricate novel optoelectronic devices.