# Effects of Three Different Withering Treatments on the Aroma of White Tea
## 3 Results and Discussion
### Comparison of the Differences in Key Odor-Active Compounds of White Teas  
Table 1 indicates 20 identified odor-active compounds with OAV \(\geq\) 1. _Dimethyl sulfide_ (cabbage), _hexanal_ (green, grassy), _(Z)-4-heptenal_ (fatty, green odor), linalool (citrus-like, flowery), geraniol (rose-like, citrus-like), and trans-\(\beta\)-ionone (flowery, violet-like) have relatively high OAVs and low threshold values. Therefore, these compounds were considered to contribute more substantially to the overall odor profile [32]. Among these compounds, floral odor-active compounds such as linalool (citrus-like, flowery), (E,E)-2,4-heptdiagnenal (fatty, flowery), benzeneacetaldehyde (fatty, flowery), and Geraniol (rose-like, citrus-like) had higher OAVs in SWT than in the others. Odor-active compounds with green odor, namely _hexanal_ (green, grassy), (E)-2-nonenal (fatty, green), and cis-3-hexenyl hexanoate (fruity green odor), had higher OAVs in WWT than in the other teas. Twenty-four odor-active compounds with FD \(\geq\) 4 were detected. _(Z)-4-heptenal_ (fatty, green odor), linalool (citrus-like, flowery), geraniol (rose-like, citrus-like), vanillin (vanilla-like, sweet), and coumarin (woodruff-like, almond paste-like) had high FD factors (i.e., FD > 128). Odor-active compounds with a floral note, such as linalool and geraniol, had high FD factors of 16-512 and 16-218, respectively. These are two key compounds producing a floral aroma [33]. A comparison of FD factors revealed that linalool and geraniol had the highest values of 512 and 256, respectively, in SWT, further explaining why the SWT had a more pronounced floral aroma. Moreover, odor-active compounds with a green odor, such as _(E)-2-hexenal_ (green, apple-like), _hexanal_ (green, grassy), and _(Z)-4-heptenal_ (fatty, green odor), generally had higher OAVs and FD factors/odor intensity in WWT than in others, further explaining the more pronounced green characteristics of WWT aroma. Notably, some compounds with pleasant odors, such as neral (citrus, soapy), vanillin (vanilla, sweet), and coumarin (woodruff-like, almond paste-like), which were identified in WWT, SWT, and IWT by GC-O, had a lower FD factor in IWT than in the other teas. Thus, the content of these pleasant odor-active compounds that are beneficial for white tea aroma could be increased in the SWT or WWT processes. The volatile compounds in tea are produced through multiple pathways; for example, vanillin synthesis pathways include not only the shikimic acid pathway through de novo synthesis of glucose but also the oxidation of cresol, capsaicin, or vanillyl alcohol [34; 35]. WWT and SWT both had additional processing compared with IWT; thus, one or more volatile synthesis pathways may have been involved, resulting in an increase in FD factors. The exact effects require further investigation. To more visually analyze the effects of floral and green odor volatile compounds on the aroma of white tea, 12 odor-active compounds were selected for comparison of concentrations, as shown in Figure 4. The concentrations of linalool, geraniol, benzeneacetaldehyde, (E,E)-2,4-heptadienal, trans-\(\beta\)-Ionone, and \(\beta\)_-myrcene_ with floral odor are shown on the left side, and it can be found that they all have higher concentrations in SWT than the other samples. The concentrations of _hexanal_, _(E)-2-hexenal_, (E)-2-nonenal, _pentanal_, _(Z)-3-hexanol_, cis-3-hexenyl hexanoate with green odor are shown on the right side, and they all have higher concentrations in the WWT than the other samples. Therefore, it can be speculated that the reason for improving the floral aroma of SWT was the increase in the concentration of odor-active compounds with floral odor caused by the sunlight withering treatment. The more pronounced grassy aroma of WWT was the increase in the concentration of odor-active compounds with grassy odor caused by the withering-tank withering treatment.