Investigation of factors affecting the stability of lysozyme spray dried from ethanol-water solutions
Formulation composition and processing conditions can be adjusted to enhance the structural integrity as well as the bioactivity of proteins in the spray drying process. In this study, lysozyme was chosen as a model pharmaceutical protein to study these aspects when spray drying from water-ethanol mixtures. The effect of formulation additives (trehalose, Tween 20 and phosphate-buffered saline) and processing conditions (inlet temperature and storage time of lysozyme in the feed solution before the spray drying process) on the protein bioactivity was investigated. The results showed that the bioactivities of spray dried lysozyme with these additives were about 5–10% higher than that without additives. The bioactivity of the spray dried lysozyme was found to increase with a decrease in the inlet temperature from 130 °C to 80 °C, with similar findings when shortening the storage time of the feed solutions prior to spray drying. Fourier Transform Infrared (FTIR) and Circular Dichroism (CD) results showed that the native structures of lysozyme were largely restored upon reconstitution of the spray dried powder in water after the spray drying process. This suggests that the bioactivity of lysozyme could be preserved adequately by optimization of both the formulation composition and process conditions even when spray drying from a water-ethanol mixture.