Harnessing Filamentous Fungi for Enzyme Cocktail Production Through Rice Bran Bioprocessing

Valorization of agri-food residues has garnered significant interest for obtaining value-added compounds such as enzymes or bioactive molecules. Rice milling by-products, such as rice bran, have limited commercial value and may pose environmental challenges. Filamentous fungi are recognized for their ability to grow on residues and for their capacity to produce large amounts of metabolites and enzymes of industrial interest. Here, we used filamentous fungi to produce enzyme cocktails from rice bran, which, due to its polysaccharide composition, serves as an ideal substrate for the growth of fungi producing cellulases and xylanases. To this end, sixteen fungal strains were isolated from rice bran and identified at the species level. The species belonged to the genera <i>Aspergillus</i>, <i>Penicillium</i>, and <i>Mucor</i>. The <i>Aspergillus</i> species displayed the highest efficiency in cellulase and xylanase activities, especially <i>A. niger</i> var. <i>phoenicis</i> and <i>A. amstelodami</i>. <i>A. terreus</i>, <i>A. tritici</i>, and <i>A. montevidensis</i> stood out as xylanolytic isolates, while <i>P. parvofructum</i> exhibited good cellulase activity. <i>A. niger</i> var. <i>phoenicis</i> followed by <i>A. terreus</i> showed the highest specific enzymatic activities of α- and β-D-galactosidase, α-L-arabinofuranosidase, α- and β-D-glucosidase, and β-D-xylosidase. Additionally, proteomic analysis of <i>A. terreus</i>, <i>A. niger</i> var. <i>phoenicis</i>, and <i>P. parvofructum</i> exoproteomes revealed differences in enzyme production for rice bran degradation. <i>A. niger</i> var. <i>phoenicis</i> had the highest levels of xylanases and cellulases, while <i>P. parvofructum</i> excelled in proteases, starch-degrading enzymes, and antifungal proteins. Finally, two <i>Penicillium</i> isolates were notable as producers of up to three different antifungal proteins. Our results demonstrate that filamentous fungi can effectively valorize rice bran by producing enzyme cocktails of industrial interest, along with bioactive peptides, in a cost-efficient manner, aligning with the circular bio-economy framework.