Laccase immobilized on chitosan-polyacrylic acid microspheres as highly efficient biocatalyst for naphthol green B and indigo carmine degradation

Abstract

Low cost and non-toxic microspheres constituted by different ratios of chitosan (Cs) and polyacrylic acid (PAA) were manufactured as carriers for laccase (Lc). The CsPAA microspheres characterization proved that the PAA content played an important role on the size, surface morphology and rheological properties, and modulated the enzyme immobilization. The immobilization of Lc involved a multi-step procedure in which the 1-ethyl-3-(3-dimethylaminopropyl carbodiimide hydrochloride (EDC) was used as “zero length” crosslinker. The product with the largest active enzyme amount (44.38 mg Lc/g dry support), and the best operational stability profile was 10CsPAALc3. Also, this product contained the lowest PAA concentration and had excellent rheological properties. Moreover, two current hazardous chemicals, indigo carmine (IC) and naphthol green B (NG), were used as model dyes in practical applications. The biocatalytic decomposition of NG and IC was 1.67 and 2.4 times faster for 10CsPAALc3 compared to the free enzyme. The kinetic profile revealed that the immobilized Lc was less prone to substrate, operational and thermal inactivation. For example, the thermal inactivation for 10CsPAALc3 decreased by approximately 25% when dyes were used as substrate and by 11.71% for ABTS, as compared with the free Lc. The recycling test showed that in 5 cycles the immobilized Lc preserves 81% with NG and respectively 72% for IC of initial activity. The results prove that the new immobilized product can be successfully used in indigoid and metal-complex dyes biodegradation.