## 3 Results and Discussion
### Aroma Volatiles in FKBT and 1Y-KBT  
According to our previous experiments, KBT has a complex volatile profile, with a high concentration of acidic volatiles. To avoid the coalition of volatiles, the acidic and neutral-basic tea volatiles were separated. First, GC-O-MS/AEDA was conducted on samples extracted through SE-SPE; all odor-active compounds with an FD value \(\geq\)16 are shown in Table 2A. For compounds that remained coeluted, reference chemicals and aroma descriptions were used to assist with identification, for example, in the confirmation of methional and elimination of dihydroactinidiolide. Despite differences in FD, all of the investigated odor-active compounds were present in both samples. Compatible with our understanding of the Keemun aroma and with the DSA results, the most frequent aroma descriptor obtained from GC-O was'sweet'. The various sweet aroma components included sulfur compounds, lactones, aldehydes, and ketones. Among them, lactones were the most abundant. In studies on odor-active compounds in black tea [(8; 9; 10; 11; 12; 13; 14; 15)], raspberry ketone and hemiarin have been reported as the primary sweet compounds; \(\beta\)-damascenone and vanillin, also common sweet compounds in black tea, were detected in this experiment. However, furanone, another common sweet component, was not detected in the current GC-O-MS experiments or in our previous study of KBT. Compounds with a floral aroma were the second most abundant, including alcohols, aldehydes, acids, and esters. The third-most common compounds were all aldehydes with  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & & & & & & \\ \hline \hline \multicolumn{1}{c}{**Name 1**} & \multicolumn{1}{c}{**CAS**} & \multicolumn{1}{c}{**RI (DB-5)**} & \multicolumn{1}{c}{**Description**} & \multicolumn{1}{c}{**FKBT (b)**} & \multicolumn{1}{c}{**FKD (c)**} \\ \hline Hexanal & 66-25-1 & 800 & 1076 & Green & NBF, AF & 16 & 8 \\ Methional & 3268-49-3 & 902 & 1459 & Sweet & NBF & 16 & 2 \\ Benzenecaetaldehyde & 122-78-1 & 1042 & 1649 & Floral  
a cucumber-like aroma; among them, (E,Z)-2,6-nonnadien has frequently been described as smelling cucumber-like in GC-O studies. Unexpectedly, another component with a cucumber-like aroma, neral, was discovered but it has not been reported. The other compounds were described as green, leather, herbal, or orange-peel-like; except for benzoic acid, all such others have been reported as odor-active compounds in black tea as cited above. Although a woody aroma was characteristic of KBT after storage, no odor-active compounds were described as woody. We previously analyzed aroma volatiles in KBT stored for 3 and 15 years through GC-O-MS and similarly discovered no woody aroma volatiles (data not shown). After 1Y-KBT concentrate was dripped onto a smelling strip, a woody aroma was smelled; therefore, the extraction method and solvent used may be appropriate. In our previous study of the key volatiles related to the storage of KBT, we observed that the concentrations of some volatiles formed through the degradation of lipids and carotenoids increased during storage. We therefore inferred woody aroma volatiles to be among them; however, in GC-O-MS, most of these volatiles did not contribute to the KBT aroma. Highly volatile compounds cannot be analyzed through methods based on solvent extraction because of the loss during the concentration and cover by the solvent peak. Therefore, a static headspace technique or SPME is generally used to trap the highly volatile compounds and supply GC-O data. In the present study, SPME was employed. Due to the matrix differences between the samples and differences among the volatiles in their degree of absorption, AEDA was not applied in the SPME-GC-O-MS and we recorded only whether aroma volatiles were perceived. Differences in the highly volatile compounds between the two samples were quantitated. As Table 2B indicates, four highly volatile compounds existed in both the FKBT and 1Y-KBT: 2-methylpropanal, 3-methylbutanal, 2-methylbutanal, and dimethyl trisulfide.