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 Aspergillus, Penicillium, and Mucor. The Aspergillus species displayed the highest efficiency in cellulase and xylanase activities, especially A. niger var. phoenicis and A. amstelodami. A. terreus, A. tritici, and A. montevidensis stood out as xylanolytic isolates, while P. parvofructum exhibited good cellulase activity. A. niger var. phoenicis followed by A. terreus 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 A. terreus, A. niger var. phoenicis, and P. parvofructum exoproteomes revealed differences in enzyme production for rice bran degradation. A. niger var. phoenicis had the highest levels of xylanases and cellulases, while P. parvofructum excelled in proteases, starch-degrading enzymes, and antifungal proteins. Finally, two Penicillium 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.

This work was supported by the project AGROALNEXT/2022/035 by MICIN with funding from the European Union NextGenerationEU/PRTR-C17.I1 and by Generalitat Valenciana. SG holds a Juan de la Cierva Incorporación grant (IJC2020-042749-I) funded by MCIN/AEI/ 10.13039/501100011033, “ERDF: A way of making Europe”, and ‘NextGenerationEU/PRTR’. The authors also acknowledge the Severo Ochoa Excellence Program CEX 2021-001189-S funded by MCIN/AEI and by “ERDF: A way of making Europe”.

With funding from the Spanish goverment through the "Severo Ochoa Centre of Excellence" accreditation (CEX 2021-001189-S)

Peer reviewed