Green aqueous biphasic systems containing deep eutectic solvents and sodium salts for the extraction of protein

Deep eutectic solvents (DESs), a new type of green solvents, were applied for the extraction of proteins with aqueous biphasic systems (ABSs) in this study. The structures of the prepared DES were confirmed by FT-IR and H-1 NMR. The DES-salt(NaH2PO4/Na2CO3/Na3C6H5O7)-based ABSs were established and applied to extract the bovine serum albumin and papain. DES-Na2CO3 ABS was selected as the suitable extraction system. Single-factor experiments were investigated to achieve complete extraction by properly tailoring the concentration of different compositions (e.g. proteins, Na2CO3, DES), the temperature and pH values. The experimental results indicated that the extraction efficiency could reach up to 95.16% for bovine serum albumin and 90.95% for papain under the optimum conditions. UV-vis spectra, fluorescence spectra and CD spectra were investigated to confirm that the conformation of bovine serum albumin did not change after extraction. The transmission electron microscopy (TEM) was used to explore the mechanism of the extraction. All of these results indicated that DES-based ABSs may provide a new possibility for the separation of proteins.