# Effects of Three Different Withering Treatments on the Aroma of White Tea
## 3 Results and Discussion
### Comparison of the Differences in the Overall Volatile Compounds of White Teas  
The three white teas detected a total of 202 compounds (Table S2). Most of the compounds were alcohols or aldehydes, which is consistent with the known aroma composition of white tea; these compounds are likely produced by the hydrolysis of glycosides, oxidative degradation of fatty acids, or carotenoids, or Maillard reactions during white tea processing [9]. The 202 volatile compounds extracted from the three samples were analyzed using PCA, and fractograms were obtained. The PCA results indicated that the first two principal components explained 51.7% and 27%, respectively, of the total variance (Figure 3A). According to the results, IWT, SWT, and WWT samples were clustered into different quadrants and well-separated, indicating that these three samples differ. The HCA results revealed that the samples were divided into three clusters; SWT samples were further divided into separate clusters, indicating greater differences among SWT samples (Figure 3B). This result is consistent with the PCA results. The volatile compounds detected in the three white teas were analyzed, and Venn diagrams depicting commonalities between the teas were drawn (Figure 3C). The three white teas shared 145 volatile compounds. SWT shared five and nine volatile compounds with WWT and IWT, respectively. WWT and IWT shared ten volatile compounds. SWT, WWT, and IWT had 16, 11, and 10 unique volatile compounds, respectively. Thus, different withering treatments can indeed result in the production of different volatile compounds. This is consistent with the results of previous studies, which have reported that different tea leaf processing methods could result in different aromas [29]. GC-MS results cannot directly confirm the degree of contribution of compounds to the aroma of a sample because of the influence of certain component thresholds. Therefore, the OAVs and FD factors were used to determine the degree of contribution of each compound to the overall aroma [30]. Volatile compounds with FD factor \(\geq\) 4 or OAV \(\geq\) 1 were defined as odor-active compounds [18]. Most of the 16 volatile compounds present in the SWT only exhibited floral or fruity aromas; these compounds include geranyl formate (fresh rose), methyl benzoate (starfruit-like and sweet), octanoic acid, methyl ester (fruity), diisobutyl phthalate (mildly fragrant), 2-phenoxy-ethanol (mild rose aroma), and 6,10-dimethyl-5,9-undecadien-2-one (sweet and rose). These results are consistent with those of QDA, indicating that the high scores for floral characteristics in the SWT could  
Figure 2: Radar plot for quantitative descriptive analysis (SWT: sunlight withering-treated white tea; WWT: withering-tank withering-treated white tea; IWT: indoor withering-treated white tea). be attributed to these volatile compounds; however, the specific contributions of these odor-active compounds require further investigation. A study demonstrated that black tea treated with red light during withering has a significantly stronger floral aroma than that treated with white light because of the effect of light on glycosidase activity [6]. Therefore, light may promote the activity of certain enzymes, resulting in increased production of corresponding volatile compounds and increasing the strength of the floral aroma of SWT. 3-Methyl-4-heptanone (nutty) is a volatile compound identified only in WWT. Table 1 indicates that this compound is odor active. Ketones are produced through the oxidation of lipids, degradation of amino acids, and the Maillard reaction [31]. The withering process was accelerated by hot air in the WWT; ketones with a nutty aroma may have been produced during this process as a result of these reactions. However, the QDA results did not indicate a significant effect on the tea aroma; this may be attributed to the interactions between compounds. Figure 3: Overall differences in volatile compounds among white teas.