Valorization of Stale Bread and Sunflower Spent Oil via Solid State Fermentation Using Food-Grade Filamentous Fungi

Global food waste management necessitates circular bioeconomy solutions to transform organic residues into high-value nutrients to address nutritional demands. This study investigated the valorization of two abundant waste streams, stale bread and sunflower oil through solid state fermentation using food-grade filamentous fungi. Three strains, Neurospora intermedia, Aspergillus oryzae and Rhizopus oryzae were evaluated for the bioconversion of stale bread. Oil supplementation levels of 10, 20 and 30% (g/100 g dry matter) using both fresh and spent sunflower oil were tested to assess changes in proximate composition, characterizing fungal growth dynamics and mycelial development. Furthermore, modifications in fatty acid profiles and hydrolytic enzyme activities were analyzed to determine species responses to oil source and concentration. The results demonstrated that N. intermedia achieved peak protein levels of 36% (g/100 g) alongside efficient starch catabolism, while 10% fresh oil supplementation induced a significant protein increase (26%) in A. oryzae. Regarding lipid accumulation, 10% spent oil supported higher fat content in R. oryzae (19%) compared to fresh oil (17%). PUFA/SFA ratio reached its maximum in A. oryzae with the highest of 5.91 ± 0.56 under 10% fresh oil. Enzymatic analysis identified A. oryzae as the most efficient lipase producer, reaching a maximum activity of approximately 0.10 U/g at 10% spent oil supplementation. Conversely, R. oryzae lipase activity peaked at 20% supplementation (0.08 U/g), reflecting its high capacity for lipid accumulation. These findings establish a potent bioprocess for upcycling mixed food wastes into enhanced functional ingredients for sustainable food and feed systems.