Journal of Tea Science Research, 2024, Vol.14, No.4, 238-248 http://hortherbpublisher.com/index.php/jtsr 239 2 Overview of Tea Plant Biology and Chemistry 2.1 Key compounds affecting tea flavor Tea flavor is primarily influenced by several key compounds, including catechins, theaflavins, amino acids, and essential oils. Catechins, a type of flavonoid, are significant contributors to the sensory qualities and health benefits of tea. They are responsible for the astringency and bitterness in tea, with epigallocatechin gallate (EGCG) being one of the most abundant and impactful catechins (Zhang et al., 2023). Theaflavins, formed during the oxidation of catechins, contribute to the color and briskness of black tea, enhancing its overall flavor profile (Hua et al., 2021). Amino acids, particularly theanine, impart a sweet and umami taste, balancing the bitterness of catechins and contributing to the overall flavor complexity (Zhang et al., 2017). Essential oils, although present in smaller quantities, provide the aromatic qualities that are crucial for the sensory experience of tea (Qu et al., 2020). The biosynthesis of these compounds is tightly regulated by environmental factors and genetic expression. For instance, the expression of catechin biosynthesis-related genes is influenced by temperature changes, which in turn affects the catechin content in tea leaves (Xiang et al., 2020). Similarly, theanine biosynthesis is modulated by factors such as temperature and the presence of growth stimulatory molecules like melatonin, which can enhance the expression of theanine biosynthesis genes under moderate high temperatures. Understanding the interplay between these compounds and their biosynthesis pathways is essential for optimizing tea quality and flavor. 2.2 Environmental factors influencing tea quality The quality and flavor of tea are significantly influenced by environmental factors such as temperature, humidity, and altitude. Optimal temperature is crucial for the growth and development of tea plants, as well as for the biosynthesis of key flavor compounds. High temperatures can negatively impact the flavonoid content, including catechins, by activating specific transcription factors that repress the jasmonate pathway, which is involved in catechin accumulation. Conversely, moderate high temperatures, when combined with exogenous melatonin, can enhance the biosynthesis of catechins and theanine, thereby improving tea quality (Li et al., 2020). Humidity and altitude also play vital roles in determining tea quality. High humidity levels can promote the growth of tea plants and the accumulation of flavor compounds, while low humidity can lead to stress conditions that may adversely affect tea quality. Altitude influences the microclimate, including temperature and sunlight exposure, which in turn affects the photosynthesis and metabolic processes in tea plants. Higher altitudes are generally associated with cooler temperatures and increased sunlight, which can enhance the synthesis of catechins and other polyphenols, leading to a richer flavor profile (Gong et al., 2020). In Wufeng Tea Garden such as those in Cangnan County, Zhejiang Province, the region's elevation is mostly above 600 meters, featuring favorable terrain, fertile soil, abundant rainfall, and ample sunlight. These factors create a microclimate highly conducive to the growth of tea plants (Figure 1). This unique ecological environment not only supports healthy tea plant development but also enhances the accumulation of flavor compounds, endowing the tea with distinctive quality characteristics. Figure 1 The ecological environment of Wufeng Tea Garden in Cangnan County, Zhejiang Province
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