Abstract

A novel melanoidin decolorizing enzyme (MDE) produced by Geotrichum sp. No. 56, which exhibits decolorization activity against synthetic melanoidin and molasses containing wastewater, was purified and characterized. The purification process was performed using ammonium sulfate fractionation, DEAE-Cellulose and Sephadex G-150 column chromatography. The melanoidin decolorization activity of the MDE was improved up to 7.3 U mg^-1, the equivalent to 8.3-fold increase from the initial protein preparation, with an overall yield of 9.1%. The results of gel filtration and SDS-PAGE revealed that the purified MDE was a dimmer with 127.5 kDa, and both subunits were alike with 63.5 kDa each. The optimum pH and temperature for the purified MDE were 6.5 and 45°C, respectively. The MDE activity was highly specific for β-D-glucose, but completely inhibited by cysteine, iodoacetic acid, 2-mercaptoethanol, gluconic acid, HgCl₂ or AgNO₃. The MDE also decolorized the spent broth of monosodium glutamate fermentation. TheGeotrichum sp. No. 56 producing MDE, which shares various characteristics with glucose oxidase (GOx), could be useful for decolorizing fermented wastewater.

Key words: Decolorization, Geotrichum sp., glucose oxidase, melanoidin, molasses wastewater.