Multi-strain solid-state fermentation combined with enzymatic hydrolysis modulates the nutritional value, flavor profile, and antioxidant capacity of walnut meal.

BACKGROUND: Walnut meal, a major by-product of oil extraction, is rich in protein and bioactive compounds but suffers from poor palatability and low digestibility due to anti-nutritional factors (ANFs) such as phytic acid, tannins, and trypsin inhibitors. Conventional processing methods fail to address these limitations fully. This study developed a sequential process combining multi-strain solid-state fermentation (using Aspergillus niger, Saccharomyces cerevisiae, and Bacillus subtilis) followed by enzymatic hydrolysis (MSSF-EH) to improve walnut meal into a flavorful, nutritious, and functional ingredient. RESULTS: Multi-omics and sensory analyses revealed that multi-strain solid-state fermentation (MSSF) reduced bitterness and astringency significantly, while increasing sourness and enriching the overall aromatic profile with roasted, nutty, sweet, and vanilla notes. Physicochemical profiling demonstrated the synergistic degradation of phytic acid, tannins, and trypsin inhibitors, alongside a 4.3-fold enrichment of lysine. Multi-strain solid-state fermentation followed by enzymatic hydrolysis triggered an increase in antioxidant capacity, driven by the liberation of phenolic monomers and short-chain oligopeptides (4-10 residues). In silico screening of the peptidome identified 14 non-toxic antimicrobial peptides such as DFAGW, WLVEDF, and FLADSFNLD. CONCLUSION: Multi-strain solid-state fermentation followed by enzymatic hydrolysis effectively transformed walnut meal into a palatable, nutrient-rich, and antioxidant-active ingredient while generating potential antimicrobial peptides. This integrated bioprocessing strategy offers a sustainable approach for improving agro-industrial by-products into high-value functional ingredients for food and feed applications. © 2026 Society of Chemical Industry.