The role of stem and leaves in shaping the integrated aroma of oolong tea.

To clarify the contributions of stems and leaves to the aroma of oolong tea, GC-MS and RNA-sequencing analyses were conducted on samples over Tieguanyin tea production. Totally, 1147 metabolites involving volatile terpenoids, fatty acids, phenylpropanoids/benzenoids, and carotenoid derivatives accounting for oolong tea aroma development, of which 21, 12 and 21 VOCs were selected as the biomarkers, and 14, 11 and 9 significant pathways enriched in the stem, 1st leaf and 2nd leaf samples respectively. Floral and fruity volatiles, including Damascone, β-Ionone, Geraniol, and Linalool, were significantly enriched in stems, while Nerolidol and α-Farnesene predominantly accumulated in leaves. Analysis of odor activity values revealed that floral-fruity volatiles were present in both stem and leaf parts, with green-leaf odors mainly preserved in the stems. However, the thermal effects in fixing and drying operations significantly reduced the abundance of green-leaf odor, while preserving most floral-fruity odor in both stem and leaf sections.