Immobilization of laccases onto cellulose nanocrystals derived from waste newspaper: relationship between immobilized laccase activity and dialdehyde content

Abstract

The purpose of this work is to evaluate the possibility of using cellulose nanocrystals (CNC) derived from waste newspaper as a carrier for immobilizing laccases. Firstly, the cellulose nanocrystals extracted from waste newspaper were oxidized with sodium periodate, and the hydroxyl groups on the second and third carbons (C2 and C3) of the CNC molecules were converted to dialdehyde groups. Then, the laccase was successfully immobilized on the dialdehyde-modified cellulose nanocrystals (DMC) through covalent bonding. The DMC was characterized using zeta potential, Fourier-transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy, and the relationship between the activity of the immobilized laccase and the dialdehyde group content of the DMC was thoroughly investigated. It was found that the yield of the laccase immobilization is 64.94%, and the highest activity of the immobilized laccase (1.108 U/mg) is obtained at an aldehyde content of the DMC equal to 50.64%, a mass ratio of the carrier to the laccase equal to 45:3, a pH of 4.5, and a reaction time of 2 h. Compared to the free laccase, the immobilized laccase exhibits excellent stability in a wider range of pH values and temperatures. Furthermore, the immobilized laccase showed excellent reusability as evidenced by its retained relative activity of 67% after 6 cycles.