## 3 Results
### Aroma-Active Compounds (AAC) in Peach-like Black Tea Samples Identified by GC-O  
GC-O (Gas Chromatography-Olfactometry) is a valuable technique for detecting and defining the flavor of the samples; it combines the separation of volatile compounds using gas chromatography with a sniffer's olfactometry sense. Therefore, we applied this technique to characterize the aroma and intensity of four kinds of JBT samples (JBT 2, JBT 3, JBT 6, and JBT 8), which all had a significant peach-like aroma in the sensory evaluation. Figure 5 shows the olfactometry results as an aroma wheel. A total of 26 kinds of aroma compounds with floral and fruity fragrances were selected as potential arom-active compounds in JBT. Interestingly, in addition to \(\delta\)-decalactone, other kinds of lactone, including \(\gamma\)-caprolactone, \(\delta\)-octalactone, and \(\gamma\)-decalactone, were identified in particular samples and were related to the peach aroma [31]. However, they were not found in GC-MS. This may have been due to the fact that these four kinds of lactones were found simultaneously only in the sample of JBT 8. This result supports the previous sensory evaluation, showing that this sample had a high and significant peach-like aroma. Apart from these, jasminlactone also showed a close peach-like aroma, and it was also detected by olfactometry in all samples. Indole and coumarin shared the same retention time in olfactometry detection, and probably due to the sensory interaction between aroma compounds, these two compounds mixed and showed a strong fragrance of peach essence rather than a real peach fruit-like aroma. \begin{table}
\begin{tabular}{c c c c} \hline
**Compounds** & **CAS** & **Class** & **VIP** & **Aroma Type** \\ \hline Methyl salicate & 119-36-8 & Ester & 6.83 & Green, holly oil-like \\
1-(2-pyridinyl)-Ethanone & 1122-62-9 & Heterocyclic compound & 4.31 & Nutty, popcorn-like \\
2H-Pyran-2-one, tetrahydro-6-methyl- & 823-22-3 & Heterocyclic compound & 4.05 & Fruity, burn-like \\
1-ethyl-3-methyl-Benzene & 620-14-4 & Aromatics & 3.71 & NF \\
2H-Pyran-3-ol, 6-ethenyltetrahydro-2,2,6-trimethyl & 14049-11-7 & Heterocyclic compound & 3.61 & NF \\ trans-Linalool oxide (furanoid) & 34995-77-2 & Heterocyclic compound & 3.60 & Floral \\ \hline \end{tabular}
\end{table} 
Table 4: VIP higher than (besides equal to) 3 compounds in FBT. \begin{table}
\begin{tabular}{c c c c c} \hline
**Compounds** & **CAS** & **Class** & **VIP** & **Aroma Type** \\ \hline Indole & 120-72-9 & Heterocyclic Compound & 7.21 & Floral \\ Methyl salicate & 119-36-8 & Ester & 6.45 & Green, holly oil-like \\ \(\delta\)-Decalactone & 705-86-2 & Ester & 4.30 & Peach-like, creamy \\ trans-beta-Octimee & 3779-61-1 & Terpenoids & 3.58 & Floral, green \\ (E)-4,8-Dimethylnona-1,3,7-triene & 19945-61-0 & Terpenoids & 3.46 & Floral \\ cis-alpha-Bisabolene & 29837-07-8 & Terpenoids & 3.17 & Green \\ Hexanoic acid, hexyl ester & 6378-65-0 & Ester & 3.00 & Fruity \\ \hline \end{tabular}
\end{table} 
Table 3: VIP higher than (besides equal to) 3 compounds in JBT. In the case of FBT, the FBT 1 sample was selected for analysis due to its significant caramel-like aroma. Only 13 kinds of known aroma compounds, which contribute to the floral and fruity aromas, were distinguished. This amount was less than that in JBT; moreover, most of them were also found in JBT. As for the potential characteristic aromatic compounds of FBT, jasminlactone (creamy, fruity) and furufural (nutty) may contribute to the caramel-like aroma to some extent. The OAVs of the potential aroma-active compounds (AAC) of the JBT were calculated by means of their Odor Thresholds (OTs). Their corresponding aroma characteristics are also described in detail in Table 5. To compare the OAV results, the mean OAVs were used. Furthermore, to compare the contribution degree of relative compounds, their ACIs were also used. Figure 5: The aroma wheel of compounds in JBT and FBT. The fruit legends represent various fruity aroma characteristics of the compounds in olfactory detection, and so as the flower legends.