Mechanistic insights into Grifola frondosa-driven fermentation of Rice-wheat bran: Metabolomic profiling, molecular dynamics, and enhanced antioxidant efficacy

Rice bran (RB) and wheat bran (WB) are rich in bioactives but poorly utilized due to limited bioaccessibility. Here, a fungal fermentation strategy was developed to valorize RB-WB blends. A novel fermented product (FRBWB) was obtained via Grifola frondosa (G. frondosa) fermentation, with conditions optimized for bioactive enrichment. After 13 days of fermentation, polysaccharide, polyphenol, and soluble protein contents increased from 86.56 to 126.93 mg/g, 1.38 to 1.67 mg/g, and 53.69 to 93.06 mg/g, respectively (P < 0.05), accompanied by marked improvements in water-holding capacity and solubility. The process altered substrate's microstructure, resulting in a looser, more porous surface. Untargeted metabolomics identified 445 differentially expressed metabolites (DEMs) between FRBWB and the unfermented control (RBWB), among which ferulic acid methyl ester showed the highest upregulation. Molecular docking and molecular dynamics simulations suggested a stable interaction between ferulic acid methyl ester and lignin peroxidase, dominated by van der Waals forces, electrostatic interactions, and hydrogen bonding (ΔE_MMPBSA = -79.73 ± 1.47 kJ/mol), which may help rationalize the observed enhancement of phenolic release. Functionally, FRBWB exhibited significantly enhanced in vitro antioxidant activity and conferred superior protection against AAPH-induced oxidative stress in zebrafish embryos, improving survival (92% at 50 μg/mL), hatching rate (87.69%), and reducing reactive oxygen species (ROS), apoptosis, and lipid peroxidation (P < 0.05). Overall, this study suggests that G. frondosa fermentation represents a sustainable strategy for upgrading RB-WB by-products into functional food ingredients with potential antioxidant benefits.