Shengyu Zhang, Hong Lei, Xingmin Gao, Xingxing Xiong, Winston Duo Wu, Zhangxiong Wu, Xiao Dong Chen
Enzyme-immobilized particles with high enzymatic activities are fundamentally and practically important for many areas, such as pharmaceuticals, medicine, and biocatalysis. In this study, by selecting trypsin and trehalose as the representative enzyme and excipient, two techniques, spray drying (SD) and spray freeze drying (SFD), have been utilized to generate enzyme-immobilized particles and comparatively studied. In both methods, uniform enzyme-immobilized microparticles are successfully obtained by using a micro-fluidic aerosol nozzle (MFAN) as the monodisperse droplet generator. The particle morphology, size and inner structure are distinctly different between the SD- and SFD-derived trypsin/trehalose composite microparticles. The former shows crumpled morphology, smaller sizes and dense inner structure while the latter shows spherical and open porous morphology with larger particle sizes. The particle formation processes in both methods are discussed. The more surface-active and large-sized trypsin molecules tend to be accumulated at the air-liquid interface of drying droplets, leading to particle buckling in SD and the formation of thin surface trypsin-enriched layer in SFD. The trypsin enzymatic activity is highly related to the presence of trehalose and the processing method. For the pure trypsin microparticles, SFD leads to a better activity preservation than SD does due to the much higher temperature adopted in SD. The presence of trehalose can significantly protect the enzymatic activity of trypsin, reaching 97.7 ± 2.6% and 97.3 ± 1.6% activity preservation with the optimal trypsin/trehalose mass ratio of 1:1 for both the SD- and SFD-derived microparticles, respectively. The protection of the enzymatic activity originates from the hydrogen bonding formation between trypsin and trehalose and the formation of highly amorphous glass matrices, which decrease enzyme unfolding and aggregation. In terms of process operability, SD offers a rather simple and economic means to produce enzymatic microparticles of high activity with the appropriate dosage of trehalose.
Particle processing, Drying technology, Uniform microparticles, Enzyme immobilization, Activity preservation