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 Mn2= 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. •Submerged fermentation of olive mill by-products was performed.•Selected white-rot fungi successfully produced laccase and manganese peroxidase.•Cerrena unicolor is the outstanding producer of laccase (78.5 U mL−1) and MnP (2.76 U mL−1).•Total phenolics reduction of 62.4–83.5% in olive pomace and wastewater was achieved.•The laccase role in the total phenolics reduction was proved.