Abstract
Enzyme-catalyzed processes are currently a powerful tool in the chemical industry due to the reduction of process time, specificity, eco-friendly characteristics, intake of low energy input, lower cost and nontoxic properties. Laccases are versatile enzymes, which catalyze oxidation reactions coupled to four-electron reduction of molecular oxygen to water. Laccases are used for decolorization and detoxification of industrial effluents and are widely used in wastewater treatment. For improving enzyme utilization in biotechnological processes, the process cost has to be reduced, the enzyme stability during industrial processes should be enhanced and the recycle and reuse step should be favorable. The immobilization of the enzyme is an important step for enhancing enzyme catalytic properties and operational stability. In our study, two different types of immobilization were used for laccase: cross-linked enzyme aggregates (CLEA) and magnetic cross-linked enzyme aggregates (mCLEA). The enzyme activity of synthesized CLEA was 0.237 U/mg laccase and mCLEA 0.637 U/mg laccase, respectively. In the next step, immobilized laccase in the form of CLEA and mCLEA was treated under supercritical conditions. Supercritical fluids (SCFs) comprise a unique class of nonaqueous media for biocatalysis and bioseparation. It is very difficult (almost impossible) to predict the stability and activity of an enzyme in any SCF at a certain pressure. Therefore, the stability of both laccase immobilized forms in supercritical carbon dioxide (SC CO2) at different pressures was studied. The highest residual activity for both laccase immobilized forms were obtained after exposure to SC CO2 at 20 MPa, 35 °C for 5 h. The obtained residual activities were 145 ± 3 % for mCLEA and 128 ± 3 % for CLEA. Improved stability of immobilized laccase in the form of CLEA and mCLEA after SC CO2 treatment indicates the possibility of using laccase in supercritical media. Further application of CLEA laccase and mCLEA laccase could be reflected in the field of hospital wastewater treatment for removal of drugs.
