This thesis deals with the preparation microparticles by spray-freeze-drying (SFD). As the process consists of various unit operations, the stability of labile APIs, such as proteins, can be serverly impaired. The secondary structure of a protein is known to be directly linked to its overall stability. However, quantification of protein secondary structure by FTIR spectroscopy can show poor reproducibility. Therefore, the first part of this thesis covers the development of a new FTIR method for objective and fast determination of protein secondary structure. The second part investigates the...