Bioscience Methods 2024, Vol.15, No.3, 114-123 http://bioscipublisher.com/index.php/bm 115 improving tea quality and health benefits. By integrating the latest research, this study provides a comprehensive understanding of the challenges and opportunities faced in tea metabolic engineering. 2 Bioactive Compounds in Tea 2.1. Key bioactive compounds: catechins, theaflavins, thearubigins, etc. Tea, derived from the leaves of Camellia sinensis, is rich in a variety of bioactive compounds, including catechins, theaflavins, and thearubigins. Tea polyphenols are compounds that possess multiple phenolic hydroxyl groups, and catechins are among the most important constituents (Chen, 2024). Catechins, such as (-)-epigallocatechin gallate (EGCG), (-)-epicatechin (EC), and (+)-catechin, are prominent in green tea and are known for their potent antioxidant properties (Punyasiri et al., 2004; Zhang et al., 2019; Samanta, 2020). Theaflavins and thearubigins, on the other hand, are formed during the fermentation process of black tea. These compounds contribute to the color and flavor of black tea and also possess significant health benefits (Zhang et al., 2019; Samanta, 2020). The transformation of catechins into theaflavins and thearubigins during tea processing is a critical aspect of tea chemistry, influencing both the sensory attributes and the bioactive profile of the final product (Zhang et al., 2019; Yu et al., 2020). In addition to these polyphenolic compounds, tea also contains other bioactive substances such as L-theanine, caffeine, and various flavonols. L-theanine, a unique amino acid found in tea, is known for its calming effects and potential health benefits, including neuroprotection and cardiovascular protection (Jeszka-Skowron et al., 2018; Li et al., 2020). Caffeine and other methylxanthines like theobromine contribute to the stimulating effects of tea and have been shown to regulate intracellular second messenger levels (Jeszka-Skowron et al., 2018; Samanta, 2020). The diverse array of bioactive compounds in tea underscores its multifaceted health benefits and its importance as a functional beverage. 2.2 Health benefits associated with bioactive compounds The bioactive compounds in tea are associated with a wide range of health benefits. Catechins, particularly EGCG, have been extensively studied for their antioxidant, anti-inflammatory, and anticancer properties. These compounds help in scavenging free radicals, reducing oxidative stress, and inhibiting the growth of cancer cells (Punyasiri et al., 2004; Wei et al., 2018; Samanta, 2020). Theaflavins and thearubigins, found in black tea, also exhibit antioxidant activities and have been linked to cardiovascular health benefits, including the reduction of blood cholesterol levels and improvement of blood vessel function (Zhang et al., 2019; Samanta, 2020). L-theanine, another significant bioactive compound in tea, has been shown to promote relaxation without drowsiness, enhance cognitive function, and provide neuroprotective effects. It also exhibits potential benefits in regulating blood pressure and supporting immune function (Jeszka-Skowron et al., 2018; Li et al., 2020). Caffeine, while primarily known for its stimulating effects, also contributes to the overall health benefits of tea by enhancing mental alertness and physical performance (Jeszka-Skowron et al., 2018; Samanta, 2020). The combined effects of these bioactive compounds make tea a valuable beverage for promoting overall health and well-being. 2.3 Factors affecting bioactive compound levels in tea The levels of bioactive compounds in tea can be influenced by various factors, including the type of tea, processing methods, and environmental conditions. For instance, green tea, which undergoes minimal oxidation, retains higher levels of catechins compared to black tea, which is fully fermented and contains higher levels of theaflavins and thearubigins (Zhang et al., 2019; Samanta, 2020). The specific processing steps, such as withering, rolling, fermentation, and drying, play a crucial role in determining the final composition of bioactive compounds in tea (Zhang et al., 2019; Yu et al., 2020). Environmental factors such as shading, temperature, and soil conditions also significantly impact the levels of bioactive compounds in tea leaves. Shading, for example, has been shown to reduce catechin levels while increasing theaflavin content in preharvest tea leaves by enhancing polyphenol oxidase activity (Liu et al., 2018; Yu et al., 2020). Additionally, the genetic makeup of the tea plant and the specific cultivar can influence the
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