Nishimura Masami, Ishiyama Kinuko, Watanabe Akiko, Kawano Setsuko, Miyase Toshio, Sano Mitsuaki
Division of Food Science and Nutrition, Nagoya Women's University, 3-40 Shioji-Cho Mizuho-ku, Nagoya 467-8610, Japan.
J Agric Food Chem. 2007 Sep 5;55(18):7252-7. doi: 10.1021/jf070312m. Epub 2007 Aug 15.
A quantitative method for four theaflavins and two methylated theaflavin derivatives in black tea leaves was developed by solid-phase extraction and a high-performance liquid chromatographic method with photodiode array detection. The theaflavins in black tea leaves were extracted three times with 40 vol 50% aqueous ethanol (mg dry tea powder/mL) containing 2% ascorbic acid. The ethanol extracts were diluted 4-fold with distilled water. All diluted extracts were directly applied to the solid-phase C18 cartridge column without concentration. The fraction of theaflavins was obtained by 40% ethanol extraction after rinsing with water followed with 15% ethanol extraction. An aliquot of theaflavins after concentration was injected onto an ODS C18 reversed-phase column, and four theaflavins and two methylated theaflavins were sufficiently separated by a linear gradient system using distilled water and acetonitrile with 0.5% acetic acid. This analytical method is sensitive for the determination of a small amount of methylated theaflavins, since various interfering substances produced during the fermentation process were eliminated in advance by solid-phase extraction. Using this analytical method, we also demonstrated that methylated theaflavins were easily produced during the manufacture of black tea.
建立了一种通过固相萃取和带光电二极管阵列检测的高效液相色谱法测定茶叶中四种茶黄素和两种甲基化茶黄素衍生物的定量方法。用含2%抗坏血酸的40体积分数50%乙醇水溶液（毫克干茶粉/毫升）对茶叶中的茶黄素进行三次萃取。乙醇提取物用蒸馏水稀释4倍。所有稀释后的提取物无需浓缩直接应用于固相C18柱。用水冲洗后，先用40%乙醇萃取，再用15%乙醇萃取，得到茶黄素馏分。浓缩后的茶黄素等分试样注入ODS C18反相柱，使用含0.5%乙酸的蒸馏水和乙腈通过线性梯度系统将四种茶黄素和两种甲基化茶黄素充分分离。该分析方法对少量甲基化茶黄素的测定具有灵敏度，因为发酵过程中产生的各种干扰物质已通过固相萃取预先消除。使用该分析方法，我们还证明了在红茶制造过程中甲基化茶黄素很容易产生。
