Tea flavor is a comprehensive representation of its aroma and other characteristics. The formation of volatile odor compounds during tea processing depends on a variety of enzymatic and non-enzymatic activities. (Z)-3-hexenol is considered the primary source of the green odor and is also the most important component in tea aroma, significantly affecting the overall aroma. However, the biosynthesis and accumulation of (Z)-3-hexenol during tea processing have not been fully analyzed. In this study, we found that withering treatment at different times and withering plus shaking treatment at different degrees promoted the accumulation of important volatile components of green tea odor, especially (Z)-3-hexenol by GC–MS. The RNA-seq and qRT-PCR results showed that withering and withering plus shaking treatments enhanced the expression of (Z)-3-hexenol-related genes in tea leaves, including synthetic pathway 1 genes (CsLOX3, CsHPL1, CsADH4, and CsAHD1), synthetic pathway 2 genes (CsGLU), and synthetic pathway 3 genes (CsCXEs). Correlation analysis of the key odorants and important genes in the three synthetic pathways revealed that some CsCXEs were positively correlated with green odor compounds. The in vitro enzyme activity results showed that rCsCXE3 (GWHTASIV011658), and rCsCXE6 (GWHTASIV031480) exhibited hydrolytic activity against three tea acetate compounds [hexyl acetate, (E)-2-hexyl acetate, and (Z)-3-hexyl acetate], resulting in the production of corresponding alcohol compounds. In summary, withering and shaking treatment during tea processing promoted the expression of CsCXE3 and CsCXE6, thereby enhancing the production of hexenol compounds. These compounds play a crucial role in increasing the green odor of tea.

中文翻译：

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CsCXEs 的生化表征：羧酸酯酶增强茶叶加工过程中绿色气味挥发物的生物合成


茶香是其香气和其他特性的综合表示。茶叶加工过程中挥发性气味化合物的形成取决于各种酶和非酶活性。（Z）-3-己烯醇被认为是绿色气味的主要来源，也是茶香气中最重要的成分，显着影响整体香气。然而，茶叶加工过程中 （Z）-3-hexenol 的生物合成和积累尚未得到充分分析。本研究发现，不同时间的萎凋处理和不同程度的萎凋加摇动处理促进了绿茶气味中重要挥发性成分的积累，尤其是 GC-MS 的 （Z）-3-己烯醇。RNA-seq 和 qRT-PCR 结果显示，凋谢和凋谢加振荡处理增强了茶叶中 （Z）-3-己烯醇相关基因的表达，包括合成途径 1 基因 （CsLOX3、CsHPL1、CsADH4 和 CsAHD1）、合成途径 2 基因 （CsGLU） 和合成途径 3 基因 （CsCXEs）。对 3 种合成途径中关键气味物质和重要基因的相关性分析表明，一些 CsCXEs 与绿色气味化合物呈正相关。 体外酶活性结果显示，rCsCXE3 （GWHTASIV011658） 和 rCsCXE6 （GWHTASIV031480） 对三种茶乙酸盐化合物 [乙酸己酯、（E）-2-乙酸己酯和 （Z）-3-乙酸己酯] 表现出水解活性，从而产生相应的醇类化合物。综上所述，茶叶加工过程中的萎凋和摇晃处理促进了 CsCXE3 和 CsCXE6 的表达，从而促进了己烯醇化合物的产生。这些化合物在增加茶的绿色气味方面起着至关重要的作用。