Prospecting fungal ligninases using corncob lignocellulosic fractions

Microorganisms play an important role in the bioconversion of organic residues and have therefore become promising for obtaining value-added enzymes. In an attempt to take advantage of the by-products and residues of bioconversion, this work sought to use lignocellulosic fractions extracted from corncob as fermentation substrate for ligninase induction by Pleurotus sajor-caju. To obtain the corncob lignocellulosic fractions, biomass was submitted to treatment by alkaline extraction (NaOH 0.75 mol L⁻¹, 55 °C for 2 h) and organosolv (40% ethanol/water, 185 °C for 20 min). The in natura biomass and lignocellulosic fractions were used as substrates in the subsequent fermentation processes: 2% in natura corncob; 2% cellulose–lignin complex fraction; 2% lignin-enriched fraction; 1% lignin-enriched fraction; and synthetic medium fungal (SMF) as standard. Chemical and physical–chemical analyses indicated the effectiveness of the lignocellulosic extraction process. According to the results, the developed system promoted the induction of ligninases by P. sajor-caju. The enzymatic analysis showed laccase production (768 U L⁻¹) using the 1% lignin-enriched fraction as substrate. Manganese peroxidase production was 1050 U L⁻¹ with the use of the 2% lignin-enriched fraction. The presence of lignocellulosic fractions extracted from corncob’s lignin-enriched fraction in the culture medium favored the induction of ligninases in comparison to the use of residue alone.