Recovery of Immunoglobulins from Bovine Serum Using Crossflow Ultrafiltration
The recovery of valuable proteins from complex feed streams is a difficult problem in the biotechnology industry. Immunoglobulins (Igs, mainly IgG) are one set of proteins that are useful for animal feedstock as nutritional additives. Bovine serum represents a potential source for Igs, however, they have to be recovered from a complex mixture of other proteins (serum albumin (BSA), α-globulins, and β-globulins) before they can be utilized as a supplement. We have been able to develop a set of physiochemical and hydrodynamic conditions for crossflow ultrafiltration to achieve a high purity (>50%) stream of IgG from bovine serum with minimal loss of yield (>70% yield). Experiments were performed on different membrane pore sizes (300 kDa and 100 kDa) while operating at different pH values near the pI of either BSA or IgG. We determined that the optimal selectivity for the non-IgG proteins (mainly BSA) occurred at a pH of 4.2 and a low ionic strength. Operating at a pH of 7.2 near the pI of IgG caused it to preferentially sieve through the membrane while the negatively charged BSA (pI ~4.8) was retained even though the molecular weights would suggest the opposite selectivity (IgG ~155 kDa vs. BSA ~66 kDa). We determined that there was no separation when the filtration was performed at an intermediate pH of 5.2. These conditions were used to develop a diafiltration procedure to recover IgG at the specified purity and yield.