## 3 Results and Discussion
### Odor-Active Compounds Determination Using GC-O  
In order to gain deep insights into the odor characteristics of the volatile compounds and further select the key odor-active compounds from the volatile compounds, GC-O analysis was performed. A total of 37 scents were perceived by GC-O in 11 SBT samples, and 35 compounds were identified using GC-MS based on their mass spectrum, _RIs_, odor characteristics, and authentic standards, and 2 compounds with moderate odor were not identified (Table 1). Among these detected compounds, \(\beta\)-ionone (AI: 9.91 \(\pm\) 0.29), (\(E\))-\(\beta\)-damascenone (AI: 9.64 \(\pm\) 0.48), linalool (AI: 8.64 \(\pm\) 0.98), linalool oxide II (AI: 8.45 \(\pm\) 0.78), epoxylinalol (AI: 7.91 \(\pm\) 0.79), linalool oxide I (AI: 7.82 \(\pm\) 0.57), dihydro-\(\beta\)-ionone (AI: 7.55 \(\pm\) 0.99), geraniol (AI: 7.36 \(\pm\) 1.55), methyl salicate (AI: 6.82 \(\pm\) 1.11), \(\alpha\)-ionone (AI: 6.36 \(\pm\) 0.98), phenylethyl alcohol (AI: 5.64 \(\pm\) 0.77), geranyl acetone (AI: 5.64 \(\pm\) 0.97), and (\(E\))-nerolidol (AI: 5.45 \(\pm\) 1.87) had higher aroma intensities, which indicated that these compounds played an important role in the formation of SBT aroma. \(\alpha\)-Ionone, \(\beta\)-ionone and dihydro-\(\beta\)-ionone, a group of carotenoid-derived aroma compounds, all presented \"woody\" and \"violet-like\" scents, which were detected in sun-dried Pu-erh tea of ancient tea plants from Bulang Mountain [25]. (\(E\))-\(\beta\)-Damascenone presented \"rose-like\" and \"sweet\" scents, with low human odor perception threshold, it was reported that (\(E\))-\(\beta\)-damascenone had a great contribution to the aroma profile of black teas [26]. Linalool presented pleasant \"floral\" and \"citrus-like\" scents, which were not only detected as key odor-active compounds in green tea, white tea, yellow tea, oolong tea, black tea, and dark tea samples [27] but also detected in flowers and spice plants [28; 29]. Linalool oxides (linalool oxide I, linalool oxide II and epoxylinalol) presented \"floral\" and \"woody\" scents, which were detected with a high concentration in semi-fermented and fermented teas [27]. Geraniol, phenylethyl alcohol, and (\(E\))-nerolidol all presented a \"rose-like\" scent, which was detected in many kinds of tea samples. Geraniol and (\(E\))-nerolidol were reported as the key odor-active compounds for the quality of black teas [30], and (\(E\))-nerolidol was also considered to be one of the key odor-active compounds for the high-quality of oolong tea [31]. Geranyl acetone presented \"rose-like\" and \"green\" scents, which were detected in black and ripened Pu-erh teas, and were considered to play an important role in the aroma profile of black and ripened Pu-erh teas [32; 33]. Methyl salicate presented \"mint\" and \"wintergreen-like\" scents, which were detected only in the teas that had a least a medium-degree fermentation but could not be detected in the green and lightly fermented teas, and it was reported that methyl salicate and (\(E\))-2-hexenal together could be used as an index to differentiate semi- and fully-fermented teas [34].  
Figure 1: The representative total ion chromatography of sun-dried black tea.