清香型乌龙茶品质形成中游离氨基酸指纹图谱变化规律

为探明游离氨基酸在茶树新梢生育过程的代谢变化及清香型乌龙茶制作工艺对其指纹图谱化学模式的影响,分别以铁观音、黄棪、金观音和黄观音品种春茶新梢为供试材料,对其新梢生育及乌龙茶制作过程中的游离氨基酸进行高效液相色谱-AQC(6-氨基喹啉基-N-羟基琥珀酰亚氨基甲酸酯)柱前衍生化检测分析。结果表明,18种已标定游离氨基酸指纹峰面积经标准化(尤其是自然对数变换)数据预处理后,再进行相似度分析(夹角余弦)、聚类分析法(欧氏距离-近邻法)和主成分分析,均可获得较为一致的可视化模式识别结果。4个茶树品种可划分为铁观音和黄棪、金观音和黄观音2个类群,不同生育期芽叶与清香型乌龙茶在制品可进行较好区分。茶氨酸、甘氨酸、谷氨酸等8种主要游离氨基酸在茶树新梢生育过程中发生较为明显的增减变化,且在中、小开面2～4叶中的含量相对较低;在清香型乌龙茶制作过程中,各主要游离氨基酸含量发生小幅变化,毛茶成品中略有增加。由此可见,游离氨基酸在茶树新梢生育过程中含量及组成的动态变化较清香型乌龙茶制作工艺的影响更为明显。该研究结果可为清香型乌龙茶鲜叶原料选取和品质工艺控制提供参考。

Variations in free amino acid fingerprints during quality formation of fresh scent-flavor Oolong tea

To investigate the metabolic alteration of free amino acids (FAA) in growing tea shoots and the production process impact on the chemical fingerprint patterns of FAA, spring shoots from the buds of Tieguanyin, Huangdan, Jinguanyin and Huangguanyin (Camellia sinensis) were harvested and processed into fresh scent-flavor Oolong tea. After pre-column derivation with 1-(quinolin-6-ylcarbamoyl)oxy]pyrrolidine-2,5- dione (AQC), FAA in samples of tea shoots and from the whole processing stages were determined with high-performance liquid chromatography. When the peak areas of the defined 18 FAAs were standardized or preferably transformed into natural logarithm, consistent visualized pattern recognitions would be obtained by either cosine similarity analysis, or nearest-neighbor cluster analysis based on Euclidean distance or principal component analysis. The samples could be divided into two groups according to the analysis. One was made up of Tieguanyin and Huangdan, and the other was Jinguanyin and Huangguanyin. Spring shoots could be distinguished well from the WIP (work in process) of fresh scent-flavor Oolong tea through their chemical patterns. The contents of 8 FAAs including theanine, glycine, glutamate and others altered obviously during shoot growth and remained rather low in banjhi buds with two to four leaves. Contents of the main FAAs did not change greatly during the process of fresh scent-flavor Oolong tea, and slightly higher content could be obtained in samples of semi-made tea than fresh leaves. These facts indicate that the contents and composition of FAAs changed more significantly during shoot growth than those in the process of fresh scent-flavor Oolong tea, and the results can provide effective references for raw material selection of fresh scent-flavor Oolong tea and its in-process quality control.