Journal of Tea Science Research, 2024, Vol.14, No.5, 249-261 http://hortherbpublisher.com/index.php/jtsr 250 relationship between fermentation conditions and the antioxidant activity of tea, providing insights into producing high-quality, health-promoting tea. 2 Chemical Changes During Fermentation 2.1 Biochemical processes in tea fermentation Tea fermentation involves a series of complex biochemical processes that significantly impact the final quality and flavor of the tea (Figure 1). During fermentation, enzymatic oxidation of polyphenols, particularly catechins, leads to the formation of theaflavins and thearubigins, which are crucial for the color and taste of black tea (Rahman et al., 2020; Hua et al., 2021). The process begins with the withering and maceration of tea leaves, which initiates the breakdown of cellular structures and the release of enzymes such as polyphenol oxidase and peroxidase. These enzymes catalyze the oxidation of catechins, resulting in the formation of various oxidation products that contribute to the tea's sensory attributes (Xu et al., 2019). Additionally, the fermentation temperature and oxygen levels play a critical role in modulating these biochemical reactions, thereby influencing the overall quality of the tea (Qu et al., 2020; Chen et al., 2021). Figure 1 The tea fermentation steps fromC. sinesnis leaves to yield different tea products in the market (Adopted from Assad et al., 2023) The research of Assad et al. (2023) outlined the distinct processing steps involved in transforming fresh Camellia sinensis leaves into four different types of tea: white, green, oolong, and black tea (Figure 1). White tea production is the simplest, involving only steaming and drying, which preserves the natural antioxidants and delicate flavor of the leaves. Green tea follows a similar process but includes an additional rolling or shaping step after steaming or roasting, enhancing its distinct taste and retaining more nutrients. Oolong tea production is more complex, involving withering, partial fermentation, tumbling, and enzymatic oxidation before drying. This process imparts a unique flavor profile that balances between green and black tea. Black tea undergoes the most extensive processing, including withering, distortion or maceration, full fermentation, and enzymatic oxidation.
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