Journal of Tea Science Research, 2024, Vol.14, No.3, 169-181 http://hortherbpublisher.com/index.php/jtsr 177 Table 1 shows the variation in the content of ten flavor-related secondary metabolites in tea plants across the spring, summer, and autumn seasons. The content of these metabolites varied significantly across different seasons, with high diversity indices and heritability. Specifically, the coefficient of variation for theanine (TN) was the highest, indicating that its content is greatly influenced by environmental factors, while catechins (C) had the highest heritability, indicating that its content is mainly controlled by genetic factors. These data provide important basis for genetic improvement of tea plants, emphasizing the necessity of selecting and cultivating high-quality tea plant varieties under different environmental conditions. 8 Analytical Techniques for Studying Tea Secondary Metabolites 8.1 Chromatography in tea metabolite analysis Chromatography is a pivotal analytical technique in the study of tea secondary metabolites. It allows for the separation, identification, and quantification of complex mixtures of compounds. Various forms of chromatography, such as gas chromatography (GC) and liquid chromatography (LC), are extensively used to analyze the flavor compounds in tea. These techniques are essential for isolating individual metabolites from the complex tea matrix, enabling detailed studies of their chemical properties and contributions to tea flavor (Zhai et al., 2022). 8.2 Mass spectrometry in tea research Mass spectrometry (MS) is another critical tool in tea metabolite research. It is often coupled with chromatographic techniques to enhance the identification and quantification of tea metabolites. MS provides detailed information on the molecular weight and structure of compounds, which is invaluable for characterizing the diverse array of secondary metabolites present in tea. The combination of MS with chromatographic techniques, such as GC-MS and LC-MS, has been particularly effective in identifying and quantifying flavor compounds in tea, including those present in trace amounts (Zhai et al., 2022). 8.3 NMR spectroscopy in tea metabolite identification Nuclear Magnetic Resonance (NMR) spectroscopy is a powerful technique for the structural elucidation of tea metabolites. NMR provides detailed information on the molecular structure and dynamics of compounds, making it an indispensable tool for identifying unknown metabolites in tea. This technique complements chromatography and mass spectrometry by providing additional structural insights that are crucial for a comprehensive understanding of tea secondary metabolites. NMR spectroscopy has been used to identify various flavor compounds in tea, contributing significantly to the knowledge of tea chemistry and flavor formation (Zhai et al., 2022). By integrating these analytical techniques, researchers can achieve a more comprehensive understanding of the biosynthesis and functional roles of secondary metabolites in tea. This multi-faceted approach is essential for advancing the field of tea research and improving the quality and flavor of tea products. 9 Case Studies 9.1 Case study 1: Catechin biosynthesis in green tea Catechins are a group of flavonoids that significantly contribute to the astringency and health benefits of green tea. The biosynthesis of catechins in green tea involves a series of enzymatic reactions that convert phenylalanine into various catechin derivatives. In a study examining the flavor determinants in green tea, it was found that the cultivar 'Bai-Sang Cha' ('BAS') contained higher levels of catechins compared to 'Fuding-Dabai Cha' ('FUD') (Han et al., 2015). This difference was attributed to the enhanced transcription of catechin biosynthetic genes in 'BAS', suggesting a genetic basis for the increased catechin production. During the manufacturing process, the levels of catechins can be influenced by the method of tea processing. For instance, steam treatment was shown to reduce the levels of catechins compared to pan-fire treatment, which consequently reduced the astringency associated with catechins (Han et al., 2015). This indicates that both genetic
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