Table_1_Unpruning improvement the quality of tea through increasing the levels of amino acids and reducing contents of flavonoids and caffeine.XLSX

Tea tree [Camellia sinensis var. sinensis or assamica (L.) O. Kuntze], an important crop worldwide, is usually pruned to heights of 70 to 80 cm, forming pruned tea tree (PTT) plantations. Currently, PTTs are transformed into unpruned tea tree (UPTT) plantations in Yunnan, China. This has improved the quality of tea products, but the underlying reasons have not been evaluated scientifically. Here, 12 samples of sun-dried green teas were manufactured using fresh leaves from an UPTT and the corresponding PTT. Using sensory evaluation, it was found that the change reduced the bitterness and astringency, while increasing sweetness and umami. Using high performance liquid chromatography detection showed that the contents of free amino acids (theanine, histidine, isoleucine and phenylalanine) and catechin gallate increased significantly (P < 0.05), whereas the content of alanine decreased significantly (P < 0.05). A liquid chromatography–mass spectrometry-based metabolomics analysis showed that the transformation to UPTT significantly decreased the relative levels of the majority of flavonols and tannins (P < 0.05), as well as γ-aminobutyric acid, caffeine and catechin (epigallocatechin, catechin, epigallocatechin gallate, gallocatechin gallate), while it significantly increased the relative contents of catechins (gallocatechin, epicatechin, epicatechin gallate and catechin gallate), phenolic acids and some amino acids (serine, oxidized glutathione, histidine, aspartic acid, glutamine, lysine, tryptophan, tyramine, pipecolic acid, and theanine) (P < 0.05). In summary, after transforming to UPTT, levels of amino acids, such as theanine increased significantly (P < 0.05), which enhanced the umami and sweetness of tea infusions, while the flavonoids (such as kaempferol, myricetin and glycosylated quercetin), and caffeine contents decreased significantly (P < 0.05), resulting in a reduction in the bitterness and astringency of tea infusions and an increase in tea quality.

茶树[Camellia sinensis var. sinensis或assamica (L.) O. Kuntze]作为全球重要经济作物，通常被修剪至70~80 cm高度，形成修剪型茶树（pruned tea tree, PTT）种植园。目前，中国云南地区正将部分PTT种植园改造为未修剪型茶树（unpruned tea tree, UPTT）种植园。此举可提升茶叶产品品质，但背后的科学机制尚未得到系统评估。本研究利用UPTT及其对应PTT的鲜叶制备得到12份日光干燥绿茶样品。经感官审评（sensory evaluation）发现，改造为UPTT后，茶叶苦涩感降低，而甜感与鲜爽度显著提升。高效液相色谱（high performance liquid chromatography, HPLC）检测结果显示，游离氨基酸（free amino acids）（茶氨酸（theanine）、组氨酸（histidine）、异亮氨酸（isoleucine）及苯丙氨酸（phenylalanine））与儿茶素没食子酸酯（catechin gallate）含量显著升高（P < 0.05），而丙氨酸（alanine）含量显著降低（P < 0.05）。基于液相色谱-质谱（liquid chromatography–mass spectrometry, LC-MS）的代谢组学（metabolomics）分析表明，改造为UPTT后，大部分黄酮醇（flavonols）与鞣质（tannins）的相对含量显著降低（P < 0.05），γ-氨基丁酸（γ-aminobutyric acid）、咖啡因（caffeine）及儿茶素类物质包括表没食子儿茶素（epigallocatechin）、儿茶素（catechin）、表没食子儿茶素没食子酸酯（epigallocatechin gallate）、没食子儿茶素没食子酸酯（gallocatechin gallate）的相对水平亦显著下降；与此同时，儿茶素类物质包括没食子儿茶素（gallocatechin）、表儿茶素（epicatechin）、表儿茶素没食子酸酯（epicatechin gallate）及儿茶素没食子酸酯（catechin gallate）、酚酸（phenolic acids）及部分氨基酸包括丝氨酸（serine）、氧化型谷胱甘肽（oxidized glutathione）、组氨酸（histidine）、天冬氨酸（aspartic acid）、谷氨酰胺（glutamine）、赖氨酸（lysine）、色氨酸（tryptophan）、酪胺（tyramine）、哌可酸（pipecolic acid）及茶氨酸（theanine）的相对含量显著升高（P < 0.05）。综上，改造为UPTT种植园后，茶氨酸（theanine）等氨基酸含量显著提升（P < 0.05），增强了茶汤的鲜爽度与甜感；而黄酮类物质包括山奈酚（kaempferol）、杨梅素（myricetin）及糖基化槲皮素（glycosylated quercetin）与咖啡因（caffeine）含量显著降低（P < 0.05），最终降低了茶汤的苦涩感，提升了茶叶整体品质。