ABSTRACT
Precipitation serves to achieve separation by the conversion of solutes to solids, which subsequently can be removed by a solid/liquid separation step. This chapter focuses on precipitation of proteins. A typical globular protein presents to the solvent a surface consisting of regions of positive and negative charge, along with polar, but uncharged, hydrophilic regions and nonpolar, hydrophobic regions. The aggregation process has been most thoroughly studied for the isoelectric precipitation of soy proteins. Aggregate growth was modeled using a mechanistic expression based on collision frequency in turbulent flow. Choice of polyelectrolyte is aided by knowledge of the isoelectric point and range of pH stability of the target protein. Acceptability of the polyelectrolyte in the product is a factor since the precipitant is at least a minor part of the precipitate. Redissolution of the precipitate and addition of multivalent salt of the opposite charge can effectively remove the polymer by forming an insoluble salt.
