Papain Immobilization on Chitosan-Coated Nylon Membrane: Preparation and Its Application in Cystatin Separation

Nylon membranes are first hydrolyed with dilute HCl and then treated with chitosan before being used as the affinity carrier. Papain as a ligand has been immobilized on the activated membranes with glutaraldehyde as a crosslinking agent. The factors involving with the activity of immobilized papain, such as concentration of glutaraldehyde, pH, temperature, reaction time, and the amount of added papain have been studied. The results show that the optimum conditions for the preparation of immobilized papain nylon affinity membranes are as follows: pH 9.0, 0.5% glutaraldehyde solution, the concentration of added papain is 10 mg/ml, the reaction time is 6 h at 45degC. The nylon membrane prepared is then used to purify cystatin from potato juice, and shows that they are high efficiency affinity membranes base for cystatin separation.