## 4 Discussion
Moreover, the total aroma content of HTS was lower than that of S (shaking alone), suggesting that high-temperature withering may counteract the positive effects of shaking. High-temperature withering accelerates water loss in tea leaves, potentially disrupting the activities of oxidase, hydrolase, and other enzymes involved in aroma anabolism [34]. For instance, higher air temperatures have been shown to decrease polyphenol oxidase activity while enhancing peroxidase activity in tea leaves [35]. Therefore, changes in enzyme activity may be the key to antagonism between shaking and high-temperature withering. Interestingly, the volatile content in HYS (high-temperature with yellow-light withering plus shaking) was similar to that of S, likely due to the counteracting effects of yellow light (which increases volatiles) and high temperature (which decreases volatiles). However, the precise mechanisms by which multiple treatments synergistically enhance black tea aroma quality require further investigation. The concentration of volatile compounds alone is not sufficient to determine their significant contribution to the overall aroma. However, our study did not conduct specialized olfactory measurements for individual compounds. In order to evaluate the contribution of specific volatiles to the overall aroma of black tea, relative odor activity values (rOAVs) were calculated based on the odor threshold and the descriptions of specific compound odor characteristics are based on references from previous literature [28]. In this study, eight volatiles were identified as the most important aroma components (rOAVs > 1). To better understand the mechanisms underlying volatile changes during different withering treatments, these eight key compounds were classified into four categories based on their sources: volatile terpenes (VTs) (e.g., linalool, cedrol, and \(\alpha\)-cedrene), amino acid-derived volatiles (AADVs) (e.g., benzeneacetaldehyde, 3-methyl-butanal, and dimethyl sulfide), carotenoid-derived volatiles (CDVs) (e.g., trans-\(\beta\)-ionone), and others (e.g., nonanal). Linalool can also be derived from the hydrolysis of glycosylated bound volatiles (GBVs) [36]. The YLS treatment showed the highest content of key VTs and AADVs, suggesting that YLS may enhance tea aroma by regulating terpenoid metabolism and amino acid degradation. VTs in tea leaves are synthesized via the methyl-erythtribosphate (MEP) and mexulonic acid (MVA) pathways. Previous research has shown that light quality (e.g., red and yellow), and shaking can significantly upregulate genes associated with VT formation [18; 26]. The higher content of VTs in YLS compared to S indicates that yellow light and shaking may synergistically regulate terpenoid metabolism, with yellow light promoting VT accumulation in the early withering stage and shaking enhancing it in the later stage. Similarly, amino acids undergo Strecker degradation under thermal conditions, producing key Strecker aldehydes such as 3-methyl-butanal, dimethyl sulfide, and benzeneacetaldehyde, with precursors that include leucine (Leu), methionine (Met), and phenylalanine (Phe), respectively [36]. Yellow-light withering [16; 27] and shaking [25] have been shown to increase the content of free amino acids, which will provide abundant precursors for AADV formation and ultimately leading to higher concentrations in black tea. The floral aroma is not only a hallmark of high-quality black tea but also a critical indicator of its excellence [37]. With the growing application of molecular sensory science in tea research, numerous studies have identified key aroma components responsible for the floral notes in black tea. For instance, indole and methyl jasmonate had been recognized as the most critical compounds determining the floral aroma intensity of Hunan black tea [15], while linalool, (E)-\(\beta\)-ionone, geraniol, \(\beta\)-myrcene, and (E)-2-hexenal, with high OAVs, have been identified as key floral volatiles in summer black tea [25].