Enhancing protein self-association at the gas–liquid interface for foam fractionation of bovine serum albumin from its highly diluted solution

Abstract

Improving foam stability is an important issue in foam fractionation of proteins from their aqueous solutions with low foam properties. In this work, enhancing protein self-association at the gas–liquid interface by sodium citrate (Na-citrate), instead of adding surfactants, was used to improve the stability of protein foams. Using bovine serum albumin (BSA) as a model protein, the role of Na-citrate in enhancing self-association of BSA at the gas–liquid interface was studied at the molecular level. Then, the role of the enhanced protein self-association in intensifying foam fractionation of BSA was studied. The results show that by weakening electrostatic repulsion between the BSA molecules and unfolding their structures, Na-citrate induced the formation of 12 and 18 BSA aggregates at the gas–liquid interface. The enhanced protein self-association effectively increased the interfacial adsorption of BSA and improved the foam stability. At BSA concentration 50mg/L, the recovery percentage of BSA with 30mmol/L Na-citrate increased by 4 folds while its enrichment ratio just decreased by 11.5%, compared to those without Na-citrate. The results give a clear understanding of the role of protein self-association in foam fractionation of proteins.