Targeting fermentation via quality indicators mapping during the overall processing of Xanthoceras sorbifolium Bunge black tea: Investigation of stable metabolic pathways and key substances

This study demonstrates flavor compound variation and the stable pattern of Xanthoceras sorbifolium Bunge Black Tea (XSBT) at different processes through multi-omics techniques. The dominant aroma compounds were identified as alcohols, aldehydes, esters, and ketones during processing and correlation analysis preliminarily shows that fermentation is the decisive stage for quality formation, as evidenced by the contents of tea polyphenols (84.98 ± 0.39 mg/g), total flavonoids (7.30 ± 0.06%) and water extracts (32.57 ± 0.45%). The flavor evolution of XSBT was mainly formed through lipid oxidation and the Maillard reaction during fermentation stage by the content alternations of aldehydes and ketones. Metabolomic interrogation of the fermentation stage further disclosed that α-linolenic acid metabolism constitutes the pivotal pathway, yielding 1-penten-3-ol and 1-penten-3-one (ROAV = 57.11) as key volatile metabolites, which reveals a stable and active lipid metabolism during fermentation. These findings could provide material, pathway and key component support for improving XSBT fermentation quality.