Fungal biorefinery for simultaneous production of enzymes and bioconversion of agro-industrial residues into renewable sugars and phenolic compounds

Abstract

Agro-industrial residues have progressed from an environmental concern toward sustainable and cost-effective sources of biopolymers and value-added chemicals. However, pre-treatments are often required for efficient extraction of the desired products from these residues. Fungal biorefinery is an interesting approach for the bioconversion of various biomasses into multiple products in a single batch. This study focuses on the utilization of six agro-industrial residues (grape pomace, sugarcane bagasse, rice husks, spent coffee grounds, residual diatomaceous earth, and wastepaper) in statistically designed combinations to evaluate the production of enzymes and the release of reducing sugars and phenolic compounds by the fungi Trametes villosa and Pycnoporus sanguineus, inoculated as mycelial pellets or mycelial discs. Both fungi demonstrated concurrent production of cellulases, pectinases, and laccases in semi-solid media, releasing sugars and phenolics from the substrates. However, each fungus exhibited distinct responses to different media compositions. P. sanguineus was the best cellulase producer, achieving a filter paper activity of 0.58 U mL−1 when inoculated as mycelial discs. T. villosa, on the other hand, excelled in producing pectinases (7.58 U mL−1 as mycelial discs) and laccases (1438 U L−1 as mycelial pellets). The highest concentrations of reducing sugars and phenolic compounds were found in extracts derived from P. sanguineus mycelial discs (37.12 mg mL−1) and T. villosa mycelial discs (0.261 mg GAE mL−1), respectively. Grape pomace and the addition of copper sulfate in the culture media consistently demonstrated their beneficial impact on the overall process.