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 and chemistries while operating at different pH values near the pI of either BSA or IgG. We developed a two step diafiltration process where the IgG and BSA were transmitted through a 300 kDa membrane while the larger α-globulins and β-globulins were retained by operating near the pI of IgG which allowed the net-neutral IgG (~155 kDa) and much smaller BSA (~66 kDa) to permeate through the membrane. We observed selectivity for the larger IgG when operating at this pH. This permeate stream served as feed for a second diafiltration process with a 100 kDa membrane operated at a pH near the pI of BSA (pI ~4.8) which made it electrostatically and sterically more favorable for the BSA to permeate through the membrane, retaining most of the IgG and therefore purifying it.