# Discovery and Flavor Characterization of High-Grade Markers in Baked Green Tea
###### Abstract  
Green tea is a popular beverage around the world and possesses a unique flavor. The flavor qualities of green tea are closely related to its grade and this relationship has not yet been studied. Three baked green teas with similar flavor were studied, namely, Huangshan Maofeng, Taiping Houkui, and Shucheng Xiaolanhua. A total of 34 odor compounds were identified by solid phase microextraction (SPME) combined with two-dimensional comprehensive gas chromatography-olfactometry-mass spectrometry analysis (GC\(\times\)GC-O-MS). The results of the clustering analysis showed that the content of D-limonene and linalool in the high-grade (Grade A) tea was much higher than the content in other grades, so they were identified as odor markers of Grade A baked green tea. The taste components of different grades of green tea infusion were analyzed by high-performance liquid chromatography-mass spectrometry (HPLC-MS) and HPLC. A combination of clustering analysis, principal component analysis (PCA), and orthogonal partial least squares discrimination analysis (OPLS-DA) indicated that galloylglucose, digalloyglucose, trisiloylglucose, strictinin, and gallic acid could be used as taste markers of Grade A baked green tea. Therefore, the results in this paper reveal the substances responsible for the odor and taste markers of high-grade baked green tea. baked green tea; odor; taste; metabolomics; GC\(\times\)GC-O-MS; HPLC-MS +
Footnote †: journal: _Molecules_  
these factors, flavor, including odor (25% of the total score) and taste (30% of the total score), is the most critical quality criteria influencing a customer's decision to purchase tea [5]. Traditionally, the discrimination of tea quality was mainly dependent on sensory evaluation and chemical detection. Among the diversiform techniques used to study the flavor of tea, GC-MS and LC-MS techniques were commonly used by researchers because they can individually identify the chemical compositions corresponding to the odor and taste in tea [6; 7]. Modern instruments can be used to effectively detect the chemical composition of tea, and the flavor quality of tea is closely related to its chemical composition [8]. So far, about 260 volatile organic compounds (VOCs) have been isolated from green tea [9], and the VOCs with relatively high concentrations contribute greatly to the odor profile of tea. Among the VOCs in green tea detected by GC-MS, the top ten relative concentrations detected are as follows: geraniol; nerolidol; linalool; cis-3-hexenyl hexanoate; nonanal; 3,7-Dimethyl-1,5,7-Octatrien-3-ol; (E)-2-hexenal; phytol; heptanal; and (Z)-jasmone [9; 10]. The tastes of green tea mainly include bitterness, astringency, umami, and a sweet after taste [11; 12]. These tastes are provided by the water-soluble compounds in tea, including phenolic compounds [13], alkaloids [14; 15; 16], amino acids [17], nucleotides and organic acids, etc. Most taste compounds have been detected by a liquid chromatographic method. A total of 24 phenolic compounds of tea were detected by high-performance liquid chromatography combined with the ultraviolet wavelength (UV) and mass spectrometry (HPLC-UV-MS) [18]. An effective liquid chromatographic method that involved precolumn derivatization with o-phthalaldehyde was developed for the determination of free amino acids in tea [19]. Teas of different quality grades are very similar in terms of their chemical components. However, they differ in terms of the concentrations of their chemical components [20; 21]. Metabolomics is an effective tool used to determine the compounds associated with tea grades. For example, the volatile composition of Yichang big-leaf green tea (YBGT) was detected by headspace gas chromatography coupled with mass spectrometry (HS-GC-MS), and based on untargeted metabolomics, 16 volatile compositions were selected as characteristic markers for distinguishing low-grade from high-grade YBGT [6].