## 4 Discussion  
Aroma is a pivotal factor in tea evaluation, directly influencing tea pricing and consumer preference. Enhancing aroma quality through innovative processing techniques is one of the most effective strategies in tea production. Withering, the first and indispensable step in black tea processing, plays a crucial role in flavor formation, as volatile components are significantly generated during this stage [11, 20]. During withering, photosynthesis, respiration, and most metabolic activities in tea leaves continue [9, 17], and these processes  
Figure 5: The relative contents of key aroma components in withered leaves and black teas: (**A**) linalool, (**B**) \(\alpha\)-cedrene, (**C**) nonanal, (**D**) trans-\(\beta\)-ionone, (**E**) benzeneacetaldehyde, (**F**) 3-methyl-butanal, (**G**) dimethyl sulfide, and (**H**) cedrol. The relative contents were presented as mean \(\pm\) SD (n = 3). Different lowercase letters above the bars in the same volatile category indicate significant differences at \(p<0.05\). N.d denotes that the component was not detected in the sample. Treatments: CK represents indoor natural withering, S represents shaking, YLS represents yellow light plus shaking, HTS represents high temperature plus shaking, and HYS represents high temperature with yellow light plus shaking. can be modulated by postharvest treatments such as shaking and light irradiation. Previous research has demonstrated that introducing shaking procedures can significantly improve black tea quality, particularly its aroma [14; 15; 25]. Consistent with these findings, this study revealed that shaking and its combinations increased the content of alcohols, aldehydes, olefins, esters, and other compounds in black tea, promoting the enrichment of floral aroma volatiles and enhancing overall aroma quality. However, the effects varied across different shaking combinations. Among the treatments, yellow-light withering combined with shaking (YLS) exhibited the most significant improvement in volatile compound formation, with the highest content of floral aroma substances in both witnessed leaves and dry black teas. This finding underscores the critical role of light quality in enhancing tea aroma and volatile metabolites [18; 26; 27; 28]. It also suggests that yellow-light withering can further amplify the floral aroma quality of shaken black tea, aligning with previous studies that supplementary LED light during the standing stage of shaking promotes volatile formation in olong tea [29]. A synergistic effect between yellow-light withering and shaking is hypothesized. During the yellow-light withering of the YLS treatment, yellow light may upregulate genes associated with volatile synthesis, such as linalool synthase genes (CsLIS2, CsLIS3, and CsLIS4) and farnesene synthase genes (CsFS5 and CsFS10), which have been reported to significantly increase under yellow light [30] and, thus, promote an increase in the content of related volatiles. As a cold light source, yellow light minimally affects leaf temperature, allowing tea leaves to remain fresh and responsive to external stresses like dehydration and mechanical damage during subsequent shaking. The dehydration and mechanical stress from shaking activate genes in volatile-related metabolic pathways [31], alters protein expression, and enhances enzyme activities that modulate volatile formation [32; 33], thereby enriching the aroma components of black tea. Thus, yellow light may play a role in the early withering stage, while shaking contributes to the later stage, collectively promoting the accumulation of aroma substances to a greater extent. In contrast, high-temperature withering combined with shaking (HTS) seemed to show an antagonistic effect. Although the aroma scores and total aroma content of HTS were higher than those of the control (CK), the content of many volatile constituents, including key aroma components such as linalool and \(\alpha\)-cedrene, decreased after withering.