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.