Biovalorization of brewer's spent grain as single-cell protein through coupling organosolv pretreatment and fungal cultivation

Abstract

Brewer's spent grain (BSG) is a clean byproduct from the food sector, comprising 85% of the brewing process solid byproducts. BSG is mainly used as low-quality animal feed and often ends up in landfills due to its short shelf life. However, considering its abundant availability and high nutritional content, BSG holds the potential for biorefineries to produce valuable products. The recalcitrant nature of BSG poses a challenge, requiring pretreatment steps. Therefore, this study focused on valorizing BSG obtained from organosolv pretreatment by producing food- and feed-grade single-cell protein (SCP). The BSG was subject to organosolv pretreatment at 180C for 2 h with 50% v/v ethanol as solvent. Filamentous fungi N. intermedia and A. oryzae were cultivated on as-received and different fractions of organosolv-treated BSG to evaluate the effect of factors such as pretreatment, fungal strain, pretreated fraction content, and substrate loading on fungal biomass yield, biomass composition (protein content), and metabolite production. A. oryzae cultivation on all tested substrates yielded 7%-40% more biomass than N. intermedia. Cultivating A. oryzae on organosolv liquor resulted in the highest biomass protein content (44.8% ± 0.7%) with a fungal biomass concentration of 5.1 g/L. A three-fold increase in the substrate loading increased the ethanol-to-substrate yield by 50%, while protein content was decreased by 23%. Finally, a biorefinery concept was proposed to integrate the organosolv pretreatment of BSG with fungal cultivation for maximum yield of SCP while obtaining other products such as lignin and ethanol, providing a sustainable rout for managing BSG.