Comparative multi-omics analysis of microbial succession, metabolite profiles, and antioxidant properties in fermented black and yellow highland barley.

Colored highland barley is rich in bioactive compounds, but fermentation-associated links among microbes, metabolites, and antioxidant properties remain unclear. Black (BHB) and yellow highland barley (YHB) were comparatively fermented using microbial profiling, non-volatile metabolomics, and antioxidant assays. Both cultivars showed reduced microbial diversity, lactic acid bacterial enrichment, fungal dominance by Saccharomycopsis, increased phenolics and anthocyanins, and decreased flavonoids. BHB retained higher flavonoid and anthocyanin contents and stronger radical-scavenging activities, whereas YHB showed greater increases in total phenolics and antioxidant capacity. Both were dominated by late-stage Pediococcus, but YHB had a denser positive bacterial network, whereas BHB showed greater modularity and enrichment of flavonoid- and phenolic acid-related metabolites. YHB was relatively associated with amino acid- and peptide-related metabolites. Lactiplantibacillus and Levilactobacillus were positively associated with selected phenolic metabolites. These findings identify common and cultivar-specific associations among microbial succession, metabolite variation, and antioxidant characteristics during colored highland barley fermentation.