Thermal and FTIR investigation of freeze-dried protein-excipient mixtures

The effect of excipients on the secondary structure of lyophilized proteins was studied through second-derivative Fourier transform infrared (FTIR) spectroscopic analysis. The glass transition temperature (T-g), denaturation temperature (T-d) and moisture content were determined by differential scanning calorimetry (DSC) and thermogravimetry (TG). T-g, T-d and the preservation of protein secondary structure were found to be dependent upon the type and amount of the excipient included in the formulation. Meanwhile, the lyophilized proteins easily adsorbed amounts of moisture during storage to reduce their T(g)s and stability.