# Effects of Monochromatic and Composite Light Withering on Black Tea Aroma
## 3 Results
### Effects of Different Monochromatic Light Withering Conditions on the Aroma of Black Tea  
To investigate the effect of different monochromatic light withering conditions on the aroma of black tea, OPLS-DA analysis was conducted on different monochromatic light treatment groups (RL, BL, and YL) and the natural light treatment group (CK), respectively. The results showed that the RL, BL and YL groups did not intersect with the CK group, proving that the OPLS-DA model could correctly distinguish the black tea withered with different monochromatic lights (Figure 3A-C). Cross-validation revealed that these three present models were not overfitted (Figure S1A-C). A total of 33 differential volatiles, mainly aldehydes and terpenoids, were found in the RL vs. CK group (Table S2, Figure 3D). Except for oct-1-en-3-ol and naphthalene, other compounds were decreased in the RL group (Figure 3E). Further analysis revealed that 11 of these substances possessed rOAVs greater than 1. Of these, eight had definite odors exhibiting fruits, almond, and grassy fragrances (Table 2). Only 15 differential volatiles were screened in the BL_vs_CK group, predominantly esters, terpenoids, and heterocyclic compounds (Table S2, Figure 3D). Interestingly, all these 15 components showed a decreasing trend in the BL group (Figure 3D,F), of which only 3 substances had an rOAV > 1, namely methylsulfanylmethane, (2E)-3,7-dimethylocta-2,6-dienal, and 2-pentylfuran. These volatiles presented cabbage, sweet, wet earth and lemon odors, separately (Table 3) [31]. In the YL_vs_CK group, 19 differential volatile compounds were screened, which were dominated by aldehydes and hydrocarbons (Table S2, Figure 3D). Among these, only naphthalene was elevated in the YL group (Figure 3G). In addition, only five substances with an rOAV > 1 presented almond, bitter, green, and fruits odors (Table 4). However, a slight difference was observed in the volatile components of different monochromatic light withering groups (Figure 3H). Figure 2: Volatile components in black tea with different lights. (**A**) Types of volatile substances in black tea withered with different lights. (**B**) PCA scores of volatile components in black tea withered with different lights. (**C**) Number of different types of volatile compounds detected in different groups. (**D**) Heatmap of differential volatiles in all groups. (**E**) Relative content of different types of volatiles (greater than 0.01 \(\upmu\)g.kg\({}^{-1}\)) in different groups. Data are means \(\pm\) SD. Bars with different letters indicate significant difference (\(p<0.05\)). \begin{table} \begin{tabular}{c c c c} \hline \hline
**Volatile Components** &
\begin{tabular}{c} **Threshold** \\ **(ug/kg)** \\ \end{tabular} & \multicolumn{2}{c}{**rOAV**} & \multicolumn{1}{c}{**Odor**} \\ \cline{2-3}
2-phenylacetaldehyde & 4 & 330.90 & 742.48 & berry, geranium, honey, nut, pungent \\
3-7-dimethyljecta-1,6-dien-3-olol & 1.5 & 377.81 & 1027.85 & amised, floral, fragrant citrus \\ (E)-hex-2-renal & 0.25 & 1208.21 & 2456.60 & almond, bitter, green, heavy, green \\
2-methylbutanol & 8.8 & 10.28 & 43.84 & almond, burrt, choking, cocoa, estery \\
3-methylbutanal & 0.25 & 227.13 & 1089.19 & apple, fermented, fruity, green grass \\
2-methylpropanal & 0.7 & 40.74 & 132.43 & burnt, caramel, cocoa, malt, \\
2-perylliumfuran & 4.8 & 3.48 & 23.21 & butter, floral, fruit, green bean \\ ocel-1-en-3-ol & 2 & 3.32 & / & / \\ (ZE)-3,7-dimethylocta-2,6-dienenanal & 5 & 2.58 & 10.74 & / \\ nonanal & 3.5 & 11.09 & 32.66 & / \\ Herptanal & 3.5 & 0.58 & 1.60 & citrus, fat, green, nut \\ \hline \hline \end{tabular}  Note: The threshold of volatile compounds in the water was reported by [PERSON] [30], the same as in Tables 3–6. Figure 3: Effects of different monochromatic light withering conditions on the aroma of black tea. The OPLS-DA score plot of the RL_vs_CK (**A**), BL_vs_CK (**B**), and YL_vs_CK (**C**) groups. (**D**) Types of differential volatile components screened from the RL_vs_CK, BL_vs_CK, and YL_vs_CK groups.