Smart nanofiltration membrane for cutting oligomeric soybean peptides

Peptides are produced through protein hydrolysis and typically contain many products of different molecular weights. In order to obtain peptide products within a specific molecular weight range, different membranes are generally used in the purification process. Here, a smart nanofiltration (NF) membrane with specific pore size under different pH conditions was proposed to separate soybean peptides. Carboxymethyl chitosan (CMCS) was introduced into the interfacial polymerization of polyamide membrane. The abundant amine groups on CMCS enabled pH-dependent conformational changes through protonation/deprotonation, thus tuning membrane surface charge and effective pore size by modulating pH of feed solution. The developed NF membrane showed that the rejection of thymopentin (679 Da) was 98.54% at pH 12 but only 40.84% at pH 3. When sequential filtrating the enzymatic hydrolysis solution at pH 12 and 3, the mass ratio of permeate soybean peptides in 189–1450 Da arrived at from 52.93% to 89.35%. The developed smart membrane simultaneously removed both large molecules and small amino acids to extract the objective peptides. A groundbreaking approach to purify biomolecules with one membrane was proposed, which would be prospective for shortening refinement processes.