关键词: 茶叶, 挥发性萜类化合物, 对映异构体, 气相色谱-质谱联用技术, 对映异构体过量值

Abstract: 【Objective】 Volatile terpenoids are important components of tea aroma, and most of them contain chiral carbon structure which lead to the existence of corresponding enantiomers with different aroma characteristics. Identifying the terpenoid enantiomers among different teas can result in a better understanding of the mechanisms underlying tea aroma formation for tea quality improvement. 【Method】 An analytical approach for enantiomeric analysis of volatile terpenoids in tea was firstly established by headspace solid phase microextraction combined with chiral gas chromatography-mass spectrometry. The chiral capillary column of Supelco β-DEX110 was used for terpenoid enantiomer analyses with corresponding authentic standards. And the compositions of enantiomers of terpenoids in representative green teas, black teas, oolong teas, white teas and dark teas were then investigated. 【Result】 Nine pairs of terpenoids enantiomers were successfully separated. The data of experiment indicated that linalool and linalool oxide B enantiomers were detected in all tea samples with high contents: S-linalool was considered as the major configuration of linalool in most kinds of teas, except for Yingde and Yunnan black teas and Indonesia white tea, which contained R-(-)-linalool as the major configuration of linalool; linalool oxide B presented the same stereo configuration in green tea, black tea, white tea and dark tea, whereas in some oolong teas (Lingtou Dancong and Wenshan Baozhong) a higher proportion of opposite configuration existed. Linalool oxide A was detected in green and dark teas with the same major stereo configuration, while it presented reverse major configuration in some black teas (Keemun and Darjeeling black teas) and oolong teas (Shuixianwudong Dancong and Tieguanyin). The single and consistent configurations of linalool oxides C and D were observed in most tea samples. The other important terpenoids distributed in various situations among different tea samples: α-pinene was only detected in the Lapsang Souchong tea, and the major configuration was S. different configurations and various enantiomeric excess values of α-terpineol were observed in different teas. R-(-)-4-terpineol was the major configurations of 4-terpineol in all tea samples, and S-(+)-4-terpineol could only be detected in the Liu Pao tea (dark tea), and a single R-configuration of α-ionone could be detected in most teas (except green teas). The quantitative results indicated that the highest contents in tea aroma of most tea samples were contributed by linalool, and the ranking order of mean contents of linalool was white tea>black tea>oolong tea>green tea>dark tea. the contents of linalool oxide B frequently second to those of linalool, and the ranking order of mean contents was black tea>white tea>oolong tea>dark tea>green tea. the contents of other terpenoids were generally lower than 100 ng·g^-1, and the content distributions were widely different among various tea samples. 【Conclusion】 This study investigated the content variations of the nine pairs of important terpenoid enantiomers in different kinds of tea for the first time. The present research result could contribute to get a deeper understanding of the chemical substances of tea aroma, and provide a new thought for the quality control of tea aroma, the discrimination of tea cultivars and origins and quality certification of tea.

Key words: tea, volatile terpenoids, enantiomers, gas chromatography-mass spectrometry, enantiomeric excess