Effect of the initial concentration on the equilibrium liquid phase concentration at salting out of proteins.

BACKGROUND: Protein precipitation is a unit operation commonly employed in bioprocesses. The most important thermodynamic property for designing an industrial precipitation operation is the solubility. The solubility is defined as the protein concentration in a certain liquid phase in equilibrium with its solid precipitate. In some cases, the protein concentration in the liquid phase at equilibrium depends on the initial concentration of the protein, therefore being an apparent solubility. Here an assessment of the effect of the molecular mass of proteins on the dependence of the apparent solubility on the initial protein concentration is reported. RESULTS: Proteins with different molecular masses (bovine insulin, 5.7 kDa; chicken egg white lysozyme, 14.7 kDa; porcine trypsin, 23.4 kDa; bovine serum albumin (BSA), 66.0 kDa) at different initial concentrations were precipitated with NaCl at constant pH and temperature. Lysozyme was the only protein that showed no change in its solubility as a function of the initial protein concentration at the studied conditions. For insulin, the effect of the initial concentration on the apparent solubility was verified only at low salt concentrations. The apparent solubility of proteins with higher molecular mass, i.e. trypsin and albumin, showed dependence on the initial protein concentration: the higher the initial protein concentration, the higher the apparent solubility. CONCLUSION: Based on the data of this work and the literature, the molecular mass appears to affect the dependence of the apparent solubility of proteins on their initial concentration in precipitation processes. © 2019 Society of Chemical Industry [ABSTRACT FROM AUTHOR]