Starter-Culture-Dependent Effects of Lactiplantibacillus plantarum and Lactobacillus delbrueckii subsp. bulgaricus Fermentation on Nutritional Quality, Flavor Characteristics and Metabolite Profiles of Flammulina velutipes Roots

Flammulina velutipes roots, abundant edible mushroom by-products, have potential for value-added utilization. This study evaluated the effects of Lactiplantibacillus plantarum (Lpb. plantarum) and Lactobacillus delbrueckii subsp. bulgaricus (Lab. bulgaricus) fermentation on the physicochemical properties, antioxidant activity, flavor characteristics, sensory characteristics, and metabolite profiles of F. velutipes roots. Fermentation significantly increased soluble dietary fiber (SDF) from 1.537 to 1.722 g/100 g and DPPH radical scavenging activity from 27.88% to 59.92% in Lpb. plantarum-treated samples. GC-IMS analysis showed that fermentation increased several flavor-active aldehydes, esters, alcohols, organic acids, and ketones, thereby improving aroma complexity. LC-MS-based untargeted metabolomics revealed that amino acid metabolism, fatty acid metabolism, organic acid metabolism, and phenylpropanoid-related pathways were closely associated with flavor formation and antioxidant enhancement. Both Lpb. Plantarum and Lab. bulgaricus fermentation enhanced the accumulation of organic acids, sugar alcohols, and aromatic precursors, supporting improved antioxidant activity. Notably, Lpb. plantarum elicited broader metabolic shifts involving hydroxy fatty acids, esters, while Lab. bulgaricus more strongly promoted organic acid and aromatic metabolite accumulation, contributing to a more acidic and malty flavor profile. Sensory evaluation and electronic tongue analysis further confirmed that fermentation enhanced aroma and palatability, while increasing sourness and reducing bitterness and astringency. These results suggest that starter-culture-dependent lactic acid bacteria fermentation is an effective strategy for improving the functional and sensory characteristics of F. velutipes root by-products.