Terahertz-time domain spectroscopy of hydrated casein and washed casein
Dynamics of hydrated casein was studied at different temperature using terahertz-time domain spectroscopy (TDS). Specifically, the effect of hydration state on unwashed and washed casein was investigated. XRF data showed that washing removed calcium atom from the casein powder. For hydrated samples, the absorbance at 1 THz of the washed casein is lower than the unwashed casein, probably due to the strengthening of the negatively charged κ-casein, which is responsible for the disruption of hydrogen bond network. No significant change was observed in dehydrated samples for both the washed and unwashed casein. Both temperature dependence of the absorbance and the spectral intensity of the imaginary part of the complex permittivity for hydrated samples show protein "dynamical transition" like behavior.