Study On The Laccase Production By Coriolus Versicolor And The Enzymatic Decolorization Of Dyes

Studiesjn this thesis were focused on the fermentation process of laccase by Coriolus versicolor, the enzymatic characteristic of laccase, and the application in dyes decolorization by laccase and laccase-mediator system. The major research achievements were as follows:(1) The optimal fermentation parameters of Coriolus versicolor in shaking flask were as follows: sucrose 1.1 g/L, glucose 1.1 g/L, bean cake powder 1.429 g/L, NaH2PO4 0.2 g/L, MgSO4.7H20 0.5 g/L and trace element 20 mL/L, initial pH 4.5; rotating speed 180 rpm, culture temperature 30℃. The activity of laccase reached 22.37 U/mL, and the production period of laccase was reduced from 14 days to 8 days.(2) The repeated batch process for laccase production was carried out in a fluidized-bed bioreactor using Coriolus versicolor pellets. The optimal conditions in the bioreactor were as follows: 30℃, pH 4.5, pellets packing ratio 1:7, aeration rate 1.0vvm. The pellets could be reused successfully at least 5 batch cycles with an average laccase yield of 5.9612 U.mL-1.d-1, which was 113.1% higher than the laccase yield obtained in shaking flask. The fluidized-bed bioreactor has advantages such as good ability of mass transport, lower energy requirement and easier purification of the product.(3) The solid-state fermentation process was studied for laccase production by Coriolus versicolor. The results showed: wheat straw was the best lignocellulosic substrate; wheat bran had an obvious stimulative effect on laccase production since it contained lots of trace elements and growth factors. The fermentation parameters were optimized as: the ratio between wheat straw and wheat bran, 50:43; water content, 70 %, fermentation temperature, 30℃. A high laccase activity (924.71 U/g) has been obtained under the optimal SSF conditions. In addition to laccase, another two kinds of enzyme (CMCase 90.85U/g and Xylanase 242.29U/g) were also detected.(4) For the oxidation-reduction reaction catalyzed by laccase, the suitable temperature was 50℃, considering the optimum temperature for laccase activity and thermal stability. The laccase-mediator system was used to decolorize two generalcommercial dyes: acrid orange and indigo. While adding 1% HBT solution (V:V) in the reactive system, 94% of acrid orange was removed in 15 minutes, which was over 48.2% higher than that without any redox mediator. Laccase couldn't decolor indigo singly, while 82.7% decolorization could be obtained with the cooperation of 2% HBT solution (V: V).Nowadays, more and more people were concerned about environmental problems, especially the wastewater containing dyestuffs. A practical way using laccase mediator system to decolorize dyestuffs was built successfully in this thesis. It had some obvious advantages such as higher efficiency and wider range of substrates. The experimental data and the technology provided in this thesis were meaningful to large-scale application of laccase in environmental protection.