Strain-complementary LAB co-fermentation valorises defatted wheat germ slurry into an antioxidant functional ingredient: Untargeted metabolomics and C. elegans evidence

Wheat germ is a nutrient-rich fraction of the wheat kernel that contains diverse bioactive constituents, and its defatted wheat germ slurry (DWGS) offers an attractive substrate for upcycling into functional ingredients. Following strain screening, we selected two DWGS-adapted lactic acid bacteria strains, Lactiplantibacillus plantarum ZJ14 (ZF) and Leuconostoc mesenteroides LH22 (LF), established both their mono-fermentation and co-fermentation systems (HF) for DWGS, and systematically compared the biotransformation effects and antioxidant activities via untargeted metabolomics and the Caenorhabditis elegans model. Compared with unfermented DWGS (WF), HF increased peptide content and degree of hydrolysis (DH) by 34.92% and 44.03%, respectively, and significantly enhanced in vitro antioxidant capacity, with DPPH scavenging activity and FRAP increasing by 40.80% and 49.82%, respectively; overall, HF outperformed the monoculture fermentations. Untargeted LC–MS/MS metabolomics further indicated that aromatic amino acid metabolism, sulfur-containing amino acid metabolism, and polyamine-related metabolic modules (including Aromatic amino acid metabolism, Phenylalanine metabolism, and Cysteine and methionine metabolism) were key pathways associated with the enhanced antioxidant phenotype of HF. In C. elegans , HF extended mean lifespan by 40.18% relative to KB and improved stress resistance, increasing mean survival time by 54.60% under heat stress (37 °C) and by 96.90% under acute oxidative stress induced by 1% H 2 O 2 (both vs KB). Consistently, HF reduced malondialdehyde (MDA) levels by 18.56% and increased the activities of antioxidant enzymes SOD, GSH, and CAT by 2.84-, 2.15-, and 1.78-fold, respectively. Transcriptional analysis suggested an insulin/IGF-1 signalling (IIS)–linked stress-response pattern, showing downregulation of upstream components ( daf-2 , age-1 , and rsks-1 ) and upregulation of core regulators ( daf-16 and skn-1 ), together with representative defence genes ( gst-4 and hsp-16.2 ). Overall, strain-complementary LAB co-fermentation provides a feasible strategy to efficiently convert DWGS into an antioxidant-oriented functional ingredient and enable high-value upcycling. • Established a strain-complementary LAB co-culture for DWGS biotransformation. • Co-fermentation (36 h) outperformed monocultures in antioxidant-oriented outputs. • Untargeted metabolomics revealed extensive remodelling of amino-acid/redox networks. • Aromatic/polyphenol-related candidates increased, aligning with stronger scavenging. • Co-fermented DWGS improved C. elegans lifespan/stress tolerance; defence genes upregulated.