Potential Degradation and Kinetics of Melanoidin by Using Laccase from White Rot Fungus

Abstract

This study was attempted to use laccase extracted from white rot fungus to remove melanoidin in the ethanol production wastewater. The isolated fungus producing the highest laccase was identified as Megaspororia sp. The highest degradation efficiencies of the purified and crude laccases were 48.00% and 44.60%, respectively. Both degradation kinetics well fit Michaelis-Menten model. The Michaelis constant (K_m) and maximum rate of reaction (V_max) were 0.82% melanoidin and 0.0045% melanoidin h^-1 for the degradation by the purified laccase and 0.71% melanoidin and 0.0037% melanoidin h^-1 for the degradation by the crude laccase. Turnover number (K_cat) of purified and crude laccases were 0.00023 and 0.00019% melanoidin U^-1 h^-1, respectively. Catalytic efficiency (K_cat/K_m) of purified and crude laccases were 0.00028 and 0.00027 U^-1 h^-1, respectively. The affinity of the crude laccase was slightly higher because of its non-specificity. K_cat and K_cat/K_m of the purified laccase were higher than the crude laccase. Proposed potential degradation result showed that laccase could oxidize CH₃, carbonyl groups, haloalkanes (C–H), C–O and C–N bondings which probably caused decolorization of melanoidin in wastewater. Thus, the purified and crude laccases can be used to decolorize melanoidin-containing wastewater from ethanol industries. As the attempt to use purified laccase consumed times and costs especially in purification steps, the crude laccase can be used to degrade color of melanoidin in wastewater with only 3.4% lower than the purified laccase.