## 4 Discussion  
### Dynamic Changes in VBs/VPs in Oolong Tea Products  
VBs/VPs play an important role in the formation of oolong tea's natural floral and fruity aroma [12]. Benzaldehyde, a key intermediate of VBs, gradually decreased in content during the solar-withering stage, but after the turnover treatment, its content significantly increased (\(p<0.01\)), indicating that the accumulation of benzaldehyde had no significant effect under light or heat stress during the solar-withering process but significantly responded to mechanical stress during turnover. However, the dynamic change in the benzyl alcohol content during the solar-withering stage was exactly the opposite of that in the benzaldehyde content, which conformed to the transformation rule of trans-cinnamic acid (PAL branch) and indirectly indicated that the solar-withering and turnover treatments were effective measures for gradually promoting the formation of VBs in oolong tea. However, [PERSON] et al. (2020) and [PERSON] et al. (2018) pointed out that the content of benzaldehyde and benzyl alcohol did not significantly change during the manufacturing process of Tieguanyin oolong tea [24,38]. This result was different from our results, which might be due to the differences in tea varieties and the intensity of the turnover treatment. Oolong tea made from the 'Huangdan' variety is famous for its strong aroma, while the 'Tieguanyin' variety has a more peaceful aroma. [PERSON] et al. (2015) found that the content of benzyl alcohol, phenylethanol, and phenylacetaldehyde in Huangdan black tea was higher than that in Tieguanyin black tea [39]. These studies suggest that the quality characteristics of the strong aroma of Huangdan oolong tea are related to the accumulation of VBs/VPs during manufacturing. More importantly, the content of benzyl alcohol in T3 was higher than that in CK3, indicating that the spreading treatment was an effective way to facilitate the accumulation of benzyl alcohol. On the contrary, in terms of VBs, there was generally a significant increase in T3, and a significant difference compared to CK3. [PERSON] et al. (2007) found that the content of benzaldehyde in tea leaves treated with turnover treatments with 5 repetitions increased by 236 times, and the content of benzyl alcohol and phenethyl alcohol also increased by 38 times and 41 times, respectively [40], in line with our results. Therefore, it is speculated that further aggravation of the mechanical stress of turnover is an effective measure for promoting the generation and accumulation of VBs/VPs. Expression Analysis and Regulation of Key CsAAAT Genes during the Post-Harvest Process of Oolong Tea  
Upregulation of key structural genes in metabolic pathways is a prerequisite for the formation and accumulation of VBs/VPs [41]. We found that both the _CsAAAT1_ and _CsAAAT2_ genes had a significantly upregulated expression during the post-harvest process of oolong tea, and there was an obvious stress response to the exogenous abiotic stress of the mechanical force of turnover. Combined with the phylogenetic tree of the _CsAAAT_ genes, the result showed that there is a highly conservative type in the sequence of the aromatic amino acid aminotransferase gene family in tea plants [42], along with a convergence effect on the expression patterns. It is important to highlight that methyl phenylacetate was