Metabolomic analysis of quality improvement through refiring in Fenghuang Dancong tea

Processing techniques determine the quality of tea. This study elucidates the impact of refiring process on Fenghuang Dancong Tea (FDT) under controlled experimental conditions by integrating sensory evaluation, non-targeted metabolomics (UPLC-MS/MS), and flavoromics (HS-SPME-GC × GC-TOF-MS). The results indicate that the decrease in polyphenols of the FDT mainly resulted from their transformation through the phenylpropanoid biosynthesis pathway during refiring, thereby reducing the bitterness and astringency of the tea while enhancing its sweetness. Although volatile diversity decreased with higher temperatures, the content of key aroma-contributing hydrocarbons and ketones peaked at 90 °C. Relative odor activity value (ROAV) analysis identified 9 key aroma compounds (ROAV ≥1), with 2-methyl-butanal, (E)-2-nonenal, 2-pentyl-furan, and 2,3-butanedione being the most impactful. This study provided a comprehensive investigation into metabolite changes during the refiring process of FDT, contributing valuable insights for precisely utilizing the refiring technique to improve the quality of tea. • Refiring significantly reduces bitterness and astringency of Fenghuang Dancong Tea (FDT), enhancing sweetness. • Non-targeted metabolomics and flavoromics reveal over 234 non-volatile and 663 volatile metabolites with significant changes. • Key metabolic pathways identified: phenolic oxidation, Maillard reaction, and changes in volatile compound profiles, shaping tea quality. • Short-term refiring at 90 °C optimizes aroma and taste while maintaining bioactive compounds, improving shelf life. • This study provides a theoretical basis for refining refiring techniques to improve the quality and shelf life of oolong tea.