Protein crystallization has drawn great attention to
replacing
the traditional downstream processing for protein-based pharmaceuticals
due to its advantages in stability, storage, and delivery. Limited
understanding of the protein crystallization processes requires essential
information based on real-time tracking during the crystallization
process. A batch crystallizer of 100 mL fitted with a focused beam
reflectance measurement (FBRM) probe and a thermocouple was designed
for in situ monitoring of the protein crystallization process, with
simutaneously record of off-line concentrations and crystal images.
Three stages in the protein batch crystallization process were identified:
long-period slow nucleation, rapid crystallization, and slow growth
and breakage. The induction time was estimated by FBRM, i.e., increasing
numbers of particles in the solution, which could be half of the time
required for detecting the decrease of the concentration, by offline
measurement. The induction time decreased with an increase in supersaturation
within the same salt concentration. The interfacial energy for nucleation
was analyzed based on each experimental group with equal salt concentration
and different concentrations of lysozyme. The interfacial energy reduced
with an increase in salt concentration in the solution. The yield
of the experiments was significantly affected by the protein and salt
concentrations and could achieve up to 99% yield with a 26.5 μm
median crystal size upon stabilized concentration readings.