Efficient production of lignin-modifying enzymes and phenolics removal in submerged fermentation of olive mill by-products by white-rot basidiomycetes

The ability of seven distinct species of white-rot basidiomycetes (WRB) to produce lignin-modifying enzymes (LME) and reduce high phenolic content was assessed during submerged fermentation of oil mill by-products. Cerrena unicolor strains appeared to be the outstanding producers of laccase (56.3-78.5 U mL(-1)) and MnP (1.03-2.76 U mL(-1)) in the fermentation of olive pomace (OP), and laccase (26.9-93.8 U mL) in the fermentation of olive tree sawdust. Diluted 50% olive mill wastewater (OMW) can be used as a nutrient medium for laccase and MnP production but its supplementation with additional carbon and nitrogen sources and Cu2+ and Mn-2= promoted the 3-, 28- and 18-fold increase of C. unicolor biomass and volumetric laccase and MnP activities, respectively, as well as 3- and 17-fold increase of Pleurotus ostreatus biomass and laccase activity, respectively. The tested fungi successfully reduced the phenolics content in the submerged fermentation of OP (72.0-81.3%) and OMW (62.4-83.5%). The laccase role in the OP phenolics reduction was proved through the treatment of 10% (wet weight) OP with commercial and lab-generated laccases preparations and reduction of total phenols by 66-70% during 24 h incubation. This work indicated that the olive mill by-products fermentation by individual substrate-specific WRB is an economically feasible and promising alternative for the simultaneous production of LME, cellulase, xylanase and detoxified materials suitable for further exploitation in biotechnological and agronomic applications.