Co-fermentation of yeast CECA and PL09 improves the flavor and functional characteristics of highland barley bran

Highland barley bran (HBB) is a nutrient-rich by-product with potential as a powdered ingredient for nutritional enhancement in liangpi, dough, and other cereal foods, but its utilization is hindered by poor flavor and palatability. HBB underwent fermentation with CECA or PL09 alone or with both yeasts (CP), enabling direct comparisons among treatments. Compared with the single-strain treatments, CP exhibited higher total phenolic and flavonoid contents, stronger DPPH and ABTS radical-scavenging activities, and greater enrichment of esters, ketones, alcohols, and aldehydes. CP24 notably accumulated several key aroma-active compounds (OAV ≥ 1), including isoamyl acetate, ethyl decanoate, ethyl hexanoate, pentanal, 2-hexenal, 2-nonenal, and 4-heptanone, imparting fruity, sweet, green, and caramel notes. Untargeted metabolomics identified 134 and 389 differential metabolites relative to CECA- and PL09-fermented HBB, respectively. Amino acid-, phenolic acid-, lipid-, and alcohol-related metabolites were closely associated with volatile formation. These improvements support HBB as a nutrient-enhancing powdered ingredient for cereal foods.