Nucleation and growth of microbial lipase crystals from clarified concentrated fermentation broths

Abstract

Bulk crystallization is emerging as a new industrial operation for protein recovery. Characterization of bulk protein crystallization is more complex than protein crystallization for structural study where single crystals are grown in flow cells. This is because both nucleation and crystal growth processes are taking place while the supersaturation falls. An algorithm is presented to characterize crystallization using the rates of the two kinetic processes, nucleation and growth. The values of these rates allow ready comparison of the crystallization process under different operating conditions. The crystallization, via adjustment to the isoelectric pH of a fungal lipase from clarified fermentation broth, is described for a batch stirred reactor. A maximum nucleation rate of five to six crystals formed per microliter of suspension per second and a high power dependency ( approximately 11) on the degree of supersaturation were found. The suspended protein crystals were found to grow at a rate of up to 15-20 nm/s and also to exhibit a high power dependency ( approximately 6) of growth rate on the degree of supersaturation.