Separation of silk proteins and silk oligopeptides by thin film composite ultrafiltration membrane

We report the synthesis of the ultrafiltration membranes prepared by an interfacial polymerization and the separation of silk proteins and silk oligopeptides by the membrane. Silk protein is produced in the degumming process from natural silk and it is discarded in silk processing wastewater even though it is a useful biopolymer. The silk proteins are degraded to a small molecular oligopeptide in an enzymatic hydrolysis reaction. Enzymes are immobilized on silica particles. And then, the enzyme-immobilized silica particles were embedded onto chitosan beads. The ultrafiltration membrane with a molecular weight cut-off in the range of 2000–3000 was synthesized by the interfacial polymerization on a porous polysulfone support. The ultrafiltration of the peptide solution allows separation of the small molecular silk oligopeptides from mixtures of high molecular weight silk proteins and low molecular weight oligopeptides. Molecular weight of the separated low molecular silk oligopeptides is lower than 3000 Da. It was observed that by in a membrane-coupled packed bed enzyme reactor, a valuable natural biopolymer could be recovered.