Revalorization of untreated Brewer’s spent grain: novel and versatile feedstock to produce cellulases, lipases, and yeast biomass in a biorefinery approach

Brewer’s spent grain (BSG) is the main by-product of the beer production industry. BSG is rich in valuable compounds, so it can be used as feedstock for the production of high value-added products. BSG was revalorized as a cost-effective, versatile, and novel media to produce lipases, cellulases, and yeast biomass. The microorganisms used were the yeasts Yarrowia lipolytica , Saccharomyces cerevisiae , Rhodotorula mucilaginosa , Hanseniaspora uvarum , and two recently isolated fungi identified as Aspergillus fumigatus and Penicillium sp. The BSG-based media allowed the production of both enzymes and yeast biomass. Y. lipolytica strains displayed similar or better lipase activity with the BSG-based media, showing that BSG can be used as carbon and nitrogen source and lipid inducer in lipases production. The highest cellulase activity on submerged fermentation was 0.354 ± 0.046 and 0.232 ± 0.004 U/mL with BSGw medium for A. fumigatus and Penicillium sp . , respectively, after 72 h. On solid-state fermentation, the cellulase activity was 7.5 ± 0.039 (11 days) and 8.3 ± 0.278 (14 days) U/g BSGw for A. fumigatus and Penicillium sp . , respectively. In yeast biomass production, S. cerevisiae had a better response in the BSG syrup production medium than R. mucilaginosa and H. uvarum , since these two strains were highly dependent on nitrogen supplementation. These results demonstrate that BSG can be used without pretreatment, as substrate for the growth of various microorganisms and as potential raw material for biorefineries, allowing the production of enzymes and single-cell biomass.