Enzymatic oxidative transformation of phenols by Trametes trogii laccases

Abstract

The removal of toxic phenolic compounds from industrial wastewater is an important issue to be addressed. Their presence in water and soil has become a great environmental concern, and effective methods for their removal need to be addressed. The feasibility of applying laccases for the degradation of phenolic compounds has received increasing attention. In the present work, the transformation of five phenolic compounds (catechol, hydroxytyrosol, tyrosol, guaiacol and p-coumaric acid), the main constituents of a typical wastewater derived from an olive oil factory, by Trametes trogii laccases was studied at concentrations ranging between 0.2 and 1.6 mM. High-performance liquid chromatography analysis showed high degradation rates of phenolic compounds by T. trogii laccases. Independently of the used concentration, a complete transformation of guaiacol, p−coumaric acid, hydroxytyrosol and tyrosol occurred after 1 h of incubation. The transformation of catechol depends on its initial concentration. The liquid chromatography-mass spectrometry analysis showed that laccases catalysed transformation of p-coumaric acid and tyrosol, resulting in the formation of phenolic dimers. No reduction of enzyme activity has been observed during the oxidation of all phenolic compounds. These results suggest that the studied laccases were capable of efficiently removing phenolic compounds, as well as catalysing the production of novel phenolic dimers.

Keywords:

• laccase
• phenols
• oxidative transformation
• removal
• polymerization

Acknowledgements

The present research study was supported by the Ministry of Higher Education and Scientific Research (MHESR) of Tunisia under the Contract Program of the Environmental Bioprocesses Laboratory, Centre of Biotechnology Sfax. We thank Mr Adel Gargoubi for technical assistance with the HPLC analysis. We also thank Mr Hedi Issawi for the mass spectrometry facilities.