Zuo Yuegang, Chen Hao, Deng Yiwei
Department of Chemistry and Biochemistry, University of Massachusetts Dartmouth, North Dartmouth, MA 02747 USA.
Talanta. 2002 May 16;57(2):307-16. doi: 10.1016/s0039-9140(02)00030-9.
A simple and fast HPLC method using a photodiode array detector was developed for simultaneous determination of four major catechins, gallic acid and caffeine. After multiple extractions with aqueous methanol and acidic methanol solutions, tea extract was separated within 20 min using a methanol-acetate-water buffer gradient elution system on a C(18) column. The sample extraction data demonstrated that the single extraction used in the previous studies with aqueous acetonitrile or methanol is not sufficient; the multiple extraction procedure is essential for the quantitative analysis of catechins, phenolic acids and caffeine in teas. Several green, Oolong, black and pu-erh teas were successfully analyzed by this method. The analytical results obtained indicated that green teas contain higher content of catechins [(-)-epigallocatechin gallate, (-)-epigallocatechin, (-)-epicatechin gallate, and (-)-epicatechin] than both Oolong, pu-erh and black teas because fermentation process during the tea manufacturing reduced the levels of catechins significantly. The fermentation process also remarkably elevated the levels of gallic acid in full-fermented pu-erh and black teas. Another interesting finding is the low level of caffeine in Oolong teas, especially in Fujian Oolong tea.
建立了一种使用光电二极管阵列检测器的简单快速的高效液相色谱法，用于同时测定四种主要儿茶素、没食子酸和咖啡因。用甲醇水溶液和酸性甲醇溶液多次萃取后，茶提取物在C(18)柱上采用甲醇 - 醋酸 - 水缓冲液梯度洗脱系统在20分钟内分离。样品萃取数据表明，先前研究中使用乙腈水溶液或甲醇进行的单次萃取并不充分；多次萃取程序对于茶叶中儿茶素、酚酸和咖啡因的定量分析至关重要。用该方法成功分析了几种绿茶、乌龙茶、红茶和普洱茶。所得分析结果表明，绿茶中儿茶素[(-)-表没食子儿茶素没食子酸酯、(-)-表没食子儿茶素、(-)-表儿茶素没食子酸酯和(-)-表儿茶素]的含量高于乌龙茶、普洱茶和红茶，因为茶叶制造过程中的发酵过程显著降低了儿茶素的含量。发酵过程还显著提高了全发酵普洱茶和红茶中没食子酸的含量。另一个有趣的发现是乌龙茶中咖啡因含量较低，尤其是福建乌龙茶。
