Chitosan crosslinked with genipin as supporting matrix for biodegradation of synthetic dyes: Laccase immobilization and characterization

Being energy-saving and environmentally friendly, laccases could be introduced as green catalysts for industrial applications. A highly stable and efficient biocatalyst for degrading synthetic dyes was designed by entrapping a purified laccase from the white rot fungus Trametes pubescens within chitosan beads grafted by the cross-linker genipin. Maximum immobilization was obtained with 0.10% (v/v) genipin and 4.0 U mL−1 of enzyme solution after activation and contact for 14 h and 6 h, respectively. Improved pH, thermal, and storage stabilities of the immobilized laccase were obtained when compared with the free counterpart. The chitosan laccase system exhibited a residual activity of >55% after 11 cycles, demonstrating better durability than the free laccase, which reflected the suitability of genipin as a cross-linker for laccase immobilization. The activity loss of free laccase after 30 days of storage at 4 °C was 84.43%, whereas the chitosan laccase system had a loss of 42.86% during the same period. The immobilized laccase alone more efficiently decolorized structurally different synthetic dyes without requiring oxidizing mediators to function in its biodegradation capability. These findings are indicative that the stability and biodegradation capability of fungal laccase can be enhanced by entrapping the enzyme within genipin-activated chitosan beads.