Upcycling Oat Hulls via Solid-State Fermentation Using Edible Filamentous Fungi: A Co-Culture Approach with Neurospora intermedia and Rhizopus oryzae

The global challenge of food insecurity requires innovative approaches for sustainable food production and waste valorization. This study investigates the valorization of oat hulls, an abundant lignocellulosic by-product from oat manufacturing, by solid-state fermentation using edible filamentous fungi. Oat hulls sourced from oatmeal industrial side-streams were used as the sole substrate in co-cultures of <i>Neurospora intermedia</i> and <i>Rhizopus oryzae</i>. The fermentation process was optimized and upscaled, with fungal growth monitored via CO₂ efflux and modeled to assess substrate utilization. Comprehensive analyses revealed a significant increase in protein concentration (<i>p</i> < 0.05) in the fermented oat hulls compared to the non-fermented controls. The resulting product was successfully incorporated into granola bars, which underwent sensory evaluation and received positive feedback, demonstrating its potential as a value-added food ingredient. These findings highlight the feasibility of using edible fungi to upcycle cereal processing by-products into nutritionally enhanced alternative protein sources, supporting both food system sustainability and circular bioeconomy objectives.