Evaluation of poly(ethylene glycol)/hydroxypropyl starch aqueous two-phase system for immunoglobulin G extraction

• Aqueous two-phase system was used to separate IgG from albumin containing feedstock.
• Hydroxypropyl starch was used as the phase-forming polymer with relatively low cost.
• NaCl addition and pH were optimized as key factors to improve the extraction of IgG.
• High purification factor of IgG was obtained with two-step extraction process.

The aqueous two-phase system (ATPS) with polyethylene glycol (PEG) and hydroxypropyl starch (HPS) was evaluated for the extraction of human immunoglobulin G (IgG) from human serum albumin (HSA). The partitions of IgG in PEG/sulphate, PEG/phosphate, PEG/Dextran and PEG/HPS ATPSs were compared, and the results indicated that PEG/HPS system was most suitable for IgG extraction. The effects of the concentrations of PEG, HPS and NaCl addition and pH on the partition of IgG and HSA in PEG/HPS ATPS were investigated. It was found that with 15% NaCl addition at pH 8.0 IgG could be largely recovered in the top PEG-rich phase and most of HSA kept in the bottom phase. In addition, the response surface methodology (RSM) was used to optimize the extraction of IgG from the protein mixture of IgG and HSA. The optimal conditions were obtained as 12% (w/w) PEG 4000, 18% (w/w) HPS and 10% (w/w) NaCl at pH 8.0. The extraction yield of IgG in the top phase was 99.2% and the purification factor could reach 5.28. The back extractions of IgG into a phosphate-rich bottom phase were also studied. The total purification factor was 5.73 with the yield of 84.0%. The results indicated that PEG/HPS ATPS might be a promising alternative for the primary recovery of IgG from the complicated feedstock.