## 3 Results and Discussion
Different letters indicates statistically significant (\(p<0.05\)). (pyranoid), 1-dodecanol, and _trans_-\(\beta\)-ionone could be the potential contributors to the aroma quality of _Tieguanyin_ black tea. Interestingly, among these potential aroma contributors, linalool, (_E_)-geraniol, and indole are EVs. Although their contents in the made teas were significantly lower than that of fresh tea leaves, they still retained a sufficient amount contributing to the aroma characteristics in the made tea. On the other hand, _trans_-\(\beta\)-ionone, \(\alpha\)-farnesene, _trans_-linalool oxide (pyranoid), and 1-dodecanol, which were NEVs produced in sufficient amount during tea processing, become aroma contributors. Although a 100% volatile recovery from dry tea to tea infusion is not plausible, considering that most of these OAVs were larger than two, thus, even with a 50% recovery rate, the OAVwould still be larger than one, and contributed to the characteristic aroma of tea infusion. Although linalool, (_E_)-geraniol, and indole were present in fresh leaves at much higher contents compared to made teas (Table 1), the fresh tea leaves did not show the pleasant aroma as the made tea did. One possibility could be that fresh tea leaves also contained other unpleasant volatiles which created masking effects. Removing or reducing these endogenous unpleasant volatiles could be an important aspect for tea processing; another possibility could be that some volatiles showed totally different characteristics in a concentration-dependent manner. One well-characterized example was indole; at very low concentrations indole had a flowery smell [39], however, in high concentrations it smelled animal-like [40]. Under our experimental conditions, only about 14% of the indole from fresh tea leaves was retained in green tea or oolong tea (Table 1). However, their OAV values in green tea and oolong still were in the ranges of 14.7-35.2 (Table 2), thus, it could confer a flowery smell to green tea or oolong tea. Four contributing volatiles, including _trans_-pyranoid linalool oxide, 1-dodecanol, _trans_-\(\beta\)-ionone, and \(\alpha\)-farnesene were only detected from certain types of made tea and with large difference in odor-activity value, suggesting that tea processing technologies determined specific NEVs formation and retention, and thus shaped the characteristic aroma for each tea type. Previously [PERSON] et al. (2013) applied simultaneous distillation extraction method and isolated volatiles from green teas, oolong teas, and black teas with various origins, then semi-quantified by two-dimensional GC-TOFMS, through multivariate data analysis the compounds with a significant difference were defined [41]. Several volatiles were commonly detected from these two studies; they can be divided into two groups. The first group showed similar changing trends among green tea, oolong tea and black tea between these two studies, including cis-linalool oxide (furanoid), trans-linalool oxide (furanoid), benzyl nitrile, methyl salicate, 2,6-dimethyl-3,7-octadien-2,6-diol, indole, cis-jasmone, \(\alpha\)-farnesene, and nerolidol; in contrast, the second group showed different changing trends among green tea, oolong tea, and black tea between these two studies, including (E)-Hotrienol, (E)-4,8-dimethyl-nona-1,3,7-triene, phenylethyl alcohol, cis-3-hexenyl hexanoate, jasmin lactone, and methyl jasmonate. Since in the previous study green tea, oolong tea and black tea came from different sources, and different cultivars may be used to produce them, this could account for the difference between these two studies. To support this notion, even within same tea type large variations have been reported in previous study [41].