Xylanase and β-glucosidase production by Aspergillus fumigatus using commercial and lignocellulosic substrates submitted to chemical pre-treatments

The composition of lignocellulosic materials used as enzyme inducers have different effects on enzyme production by fungal cultures. This work reports a comparative study of different cultivation systems for the production of xylanase and β-glucosidase by the fungus Aspergillus fumigatus SCB4 during solid-state fermentation (SSF), using sugarcane bagasse (SCB) or commercial substrates (Kraft pulp and Avicel). SCB was submitted to chemical pretreatments with H2O2, NaOH and ethanol (organosolv) and pretreated SCB samples were subsequently employed for the synthesis of enzymes. Pretreatments were efficient in the lignin reduction. Among them, the alkaline pretreatment was the most efficient with a reduction of 81.9% of lignin content in NaOH pretreated SCB in comparison to untreated SCB. In NaOH alkali-pretreated SCB, the fibers structure were also more efficiently altered with disrupted arranges and increased porosity. Despite the structural advantages obtained after pretreatments, the enzymatic biosynthesis was favored in cultivations using untreated SCB and commercial substrates as carbon sources. For β-glucosidase, it was noted a peak of production of 30.52 U/g after 96 h of SSF using untreated SCB as substrate. For xylanase, the maximum activity was detected using Kraft pulp (1878.76 U/g of substrate) after 120 h of SSF, probably due to the high concentration of hemicelluloses (19.52%) and low quantity of lignin (1.3%) in this material. Fermentations with untreated SCB also showed high xylanase activities (1647.20 U/g after the same period of incubation). This minor enzymatic biosynthesis after SSF using pretreated SCB might be due to the presence of some inhibitors produced after pretreatments which could be restricting fungal growth and consequently, the production of enzymes.