Protease immobilization on activated chitosan/cellulose acetate electrospun nanofibrous polymers: Biochemical characterization and efficient protein waste digestion

Abstract In this paper, a Serratia marcescens fibrinolytic protease KD was covalently immobilized onto the electrospun prepared glutaraldehyde (GA)-functionalized chitosan/cellulose acetate membrane nanofibres. Enzyme immobilization has been optimized at some conditions such as different GA values, different crosslinking times, different enzyme and pH values, and different times of immobilization. Results exhibited that the optimized immobilization conditions were obtained in 5.0% GA, after 4 h of crosslinking time, after 8 h immobilization time, using 210 mg protein/g support at pH 9.0. Based on these optimal conditions, the best encapsulation yield (EY) and activity recovery (AR) were obtained about 85% and 121.3%, respectively. The immobilized protease showed a 52% enhancement in protease activity than the free protease in pH 10. Furthermore, results displayed that the V max values of free and immobilized enzymes towards casein were gained 0.491 and 0.79 µmol/min, respectively. Moreover, the activity of immobilized protease was retained about 75% after incubation at 60 °C for 180 min at pH 9.0, in which the free protease only preserved about 20% of its primary activity. Results exhibited that the protease-NFs kept nearly 73% of its initial activity after three weeks of storage, while the free protease retained about 20% of its initial activity at the same condition. Results showed that the free protease exhibited 31% clot lysis, whereas the immobilized enzyme exhibited 39% clot lysis. The highest hydrolysis value of both proteases was done 17 and 48% after 4 h at 40 °C, respectively. These results indicated that Chit/CA electrospun nanofibres are excellent membranes for protease immobilization with high application in the digestion of protein waste.