Abstract
Brewer’s spent grain (BSG), the primary byproduct of beer brewing, is typically underutilized despite its rich nutrient content. This study presents a dual valorization strategy using the edible fungus Pleurotus ostreatus through solid-state fermentation (SSF) and submerged fermentation (SMF). In SSF, supplementing BSG with wheat bran yielded mushroom fruiting bodies with up to 46% biological efficiency, containing 22–26% protein, 25–29% β-glucans, and enhanced umami and antioxidant properties. In SMF, BSG-derived liquid media supported the production of up to 129 g/L wet mycelial biomass in 10 days, with the dried biomass comprising 33–38% protein, 11–15% β-glucans, and moderate antioxidant and flavor potential. Both products exhibited favorable mineral compositions and high-value bioactive compounds. In comparison, the fruiting bodies contained higher levels of free amino acids and 5′-nucleotides than the mycelium, resulting in significantly greater equivalent umami concentration. Overall, both SSF and SMF proved to be effective and complementary strategies for converting BSG into nutritious, flavor-enhancing fungal products, offering a sustainable, food-grade solution for brewery waste valorization.