High-value utilization of brewers' spent grain in extruded corn-based foods: physicochemical, functional, and metabolomic insights

The high-value utilization of brewers' spent grain (BSG), a protein- and polyphenol-rich by-product of the brewing industry, holds great promise for developing functional foods. In this study, BSG was incorporated into extruded corn-based products at varying levels (0-35 wt%), and its effects on physicochemical properties, antioxidant capacity, α-amylase inhibition, and metabolic profile were systematically investigated. The inclusion of BSG significantly improved water- and oil-holding capacities, total dietary fiber, and total phenolic content (TPC), with 30 wt% identified as an optimal formulation balancing functionality and sensory acceptability. Following in vitro digestion, the BSG-enriched extrudates exhibited significantly enhanced antioxidant activity (FRAP and DPPH assays) and α-amylase inhibitory potential, supporting their hypoglycemic potential. UHPLC-MS-based untargeted metabolomics further revealed key bioactive compounds, including 9-cis-retinoic acid and tryptophylproline, contributing to the enrichment of immune- and glucose-regulating pathways (e.g., intestinal IgA, PI3K-Akt, FoxO signaling). These results highlight the potential of BSG-fortified extrudates as value-added, fiber-enriched functional foods and provide mechanistic insights for their future nutritional development and clinical evaluation.