Statistically assisted optimisation for the simultaneous production of Trichoderma harzianum and Aspergillus fumigatus cellulolytic enzymes

This study aimed to identify the ideal conditions for producing extracellular enzymes of Trichoderma harzianum and Aspergillus fumigatus by solid-state fermentation using untreated oil palm leaves as the substrate. The solid-state fermentation (SSF) process, which produces high yields of the fungal enzymes, was optimised for parameters, such as initial medium pH, initial moisture content, and inoculum size, via a three-level-three-factor Box-Behnken design (BBD). Results revealed that the fermentation medium’s initial moisture content significantly impacted the fungal enzymes’ activities, followed by the inoculum size and initial basal pH. The T. harzianum produced cellulases at optimal SSF conditions of pH 6, an inoculum size of 5 × 10 7 spore/g substrate, and 60% moisture content, yielding 347.15 ± 15.94 U/g EGase, 20.80 ± 1.55 U/g BGase, and 221.55 ± 10.41 U/g FPase. Conversely, the A. fumigatus required a different optimised condition, viz. 1.25 × 10 8 spore/g substrate and a 60% initial moisture content at pH 3 for the highest xylanase and β-glucosidase yield at 388.88 ± 19.01 U/g and 18.74 ± 1.84 U/g, respectively. Additionally, the study discovered that the freeze-drying method enables long-term enzyme storage possible, preserving the enzymatic activities up to 93.27%. The study findings conveyed that the T. harzianum and A. fumigatus are prolific endoglucanase and xylanase producers, with possible use for agro-biomass saccharification to produce biofuel. Graphical Abstract