Abstract
The aim of this study was to investigate the effect of the composition of formulations on the properties of freeze-dried protein-excipient mixtures. Lysozyme, hyaluronidase, chymotrypsinogen A, and thermolysin were chosen as model proteins. Various excipients, including saccharides and polymers, were used to protect proteins during freeze-drying and subsequent storage. The morphology and surface of freeze-dried mixtures observed by scanning electron microscopy (SEM) displayed quite different morphologies, primarily depending on the excipient and protein used. The effects of excipients on the secondary structure of lyophilized protein were investigated with second-derivative Fourier transform infrared (FTIR) spectroscopic analysis. The glass transition temperature (Tg), denature temperature (Td) and residual moisture content were determined by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The preservation of the secondary structure of protein, Tg and Td were found to be dependent upon the type and amount of excipient included in the formulation.
