Integrated metabolomics and molecular docking reveal fermentation-dependent flavonoid transformation and bitterness attenuation in Eucommia ulmoides dark tea

This study was conducted to elucidate the fermentation-dependent remodeling of sensory attributes, non-volatile metabolites, flavonoid profiles, and bitterness-related mechanisms in Eucommia ulmoides dark tea processed at different fermentation degrees, including non-fermented tea (NFT), slightly fermented tea (SFT), fungal flowered tea (FFT), and prolonged fermentation tea (PFT). Fermentation was found to markedly reshape the taste profile of Eucommia ulmoides dark tea, with bitterness, sweetness, saltiness, and complexity being progressively reduced, whereas sourness and umami were enhanced, particularly in PFT. A total of 1799 non-volatile metabolites and 102 flavonoid metabolites were identified. Slightly fermented stage favored the accumulation of flavonoids, with the total flavonoid content reaching the highest level in SFT (4703.77 ± 15.75 mg/kg), representing increases of 188.26%, 52.13%, and 137.58% compared with NFT, FFT, and PFT. Molecular docking analysis indicated that catechin, (−)-epicatechin, isoorientin, and hesperidin may interact with the T2R14 receptor with relatively strong predicted binding affinities.