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theses

Green tea is a widely consumed tea category in China and many other countries worldwide. Usually, green tea only has few processing steps, which can mostly preserve the original compounds of fresh tea leave. Regarding the tea raw materials’ tenderness, flavor, taste and appearance, for each kind of green tea, it can be classified as different grades. Huangshan-Maofeng (HSMF) tea is a very famous and typical pan-fried green tea in China. The fresh tea leaves go through three processes, as the order of fixation, rolling and drying to obtain the final green tea product. The best or high grade of HSMF tea is usually labelled as "tè" (T), which means the special high grade of tea. The HSMF tea could be rated as six grades, "T1, T2, T3, 1, 2, 3" ordered from the high to low grade. The price of HSMF tea is highly correlated to its grade, which mainly depends on the sensory evaluation.
Recently, we just studied the metabolomics of black tea and the chemical contributors of glucose-producing enzymes inhibition effect. Similarly, the metabolomics can also be used in exploring the marker compounds, especially the minor or trace composition of tea under different treatments, or from different geographical locations. Combining with the chemical standards, tea plant chemistry database, and mass fragment regulations of typical types of secondary metabolites of tea plant, many marker compounds have been identified from tea. To find the grade-related compounds of tea, metabolomics could also be a potent tool.
The taste of tea infusion is tightly correlated to the non-volatile compounds of tea. There have been some studies about the non-volatile flavor compounds of tea, such as L-theanine, galloylated catechins, caffeine, and flavonoid glycosides. Usually, caffeine is the major bitter compound of tea, while L-theanine is a vital umami factor for the fresh taste of green tea. In this decades, it was reported that flavonoids glycosides in addition contributed to the astringency of black tea, though galloylated catechins and procyanidins are also astringent compounds which can cause the strong mouth-drying feeling in some low-grade of tea. To connect the chemical composition and taste of tea infusion, except for the classic threshold studies, the metabolomics analysis combining with sensory evaluation could also be promising.
In this research, the different grades of HSMF green tea were studied by LC-MS based metabolomics, and then the critical compounds responsible for the classification of tea grades were identified by chemical standard or related database.

ETD_10341

M.S.

Includes bibliographical references

doi:10.7282/t3-a3fh-4w20

ETD graduate

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