Immobilization of laccase onto chitosan beads to enhance its capability to degrade synthetic dyes

Loss in activity and denaturation remain key challenges to the potential use of laccase in industrial applications. One of the most important aims of enzyme technology is to enhance the stability and reusability of enzymes through immobilization processes. Here, a purified laccase (Tplac) from the white rot fungus Trametes pubescens was entrapped onto chitosan beads with the crosslinker glutaraldehyde, in order to improve the stability and recovery rate of Tplac, and was applied in decolorization of various synthetic dyes. The optimal conditions for Tplac immobilized onto chitosan beads were 0.8% (v/v) glutaraldehyde concentration, 3 h crosslinking time, 2 mL enzyme solution (approximately 43.672 U/mL), and 4 h immobilization time. The pH adaptability and resistance to thermal denaturation of immobilized Tplac were considerably enhanced compared with free Tplac, and both the operational stability and durability during multiple reuses were superior to those of free Tplac; after six cycles of continuous use, the activity of immobilized enzyme remained above 60%. Also, immobilized Tplac was able to degrade various synthetic dyes, especially metal-complex dye Acid Black 172. Results of this study demonstrated that, alongside the better stability and reusability of immobilized Tplac, the immobilized enzyme could be used in many applications.