Journal of Tea Science Research, 2024, Vol.14, No.6, 344-352 http://hortherbpublisher.com/index.php/jtsr 345 structure and regulatory genes, multi-omics technology, and novel regulatory factors such as non-coding RNAs and epigenetic modifications. With the addition of genomics, transcriptomics, and metabolomics information, this study aims to provide a comprehensive perspective of catechin metabolism and offer strategic recommendations for tea breeding superior, functional tea cultivars. 2 Types and Functional Characteristics of Catechins in Tea Plants 2.1 Major types and relative contents of catechins Camellia sinensis tea crops produce several major catechins, including epicatechin (EC), epigallocatechin (EGC), epicatechin gallate (ECG), and epigallocatechin gallate (EGCG) (Jin et al., 2023). EGCG is typically the most abundant, especially in green tea, and its formation is achieved through some routes of the flavonoid biosynthesis pathway (Ahmad et al., 2020). Galloylated catechins (EGCG, ECG) contribute up to 75% of the soluble catechins in the tea leaf, while the total catechins are responsible for 8-24% of dry leaf weight (Ahmad et al., 2020). The ratio of each catechin is relative to the tea variety, leaf development stage, and environmental conditions such as light and temperature (Xiang et al., 2021). 2.2 Role of catechins in tea quality Catechins are key determinants of tea’s sensory qualities, particularly astringency and bitterness (Ahmad et al., 2020). Galloylated catechins (EGCG, ECG) contribute most to astringency and the characteristic taste of green tea (Ahmad et al., 2020). The enzymatic oxidation of catechins during tea processing leads to the formation of theaflavins and thearubigins, which are important for the color and flavor of black and oolong teas. Genetic variation in catechin biosynthetic genes, such as F3′,5′Hand CHS, influences catechin content and thus tea quality, providing targets for breeding programs (Jiang et al., 2020). 2.3 Nutritional and pharmacological activities of catechins Catechins, especially EGCG, exhibit strong antioxidant, anti-inflammatory, and anticancer properties (Rashidinejad et al., 2021). They neutralize reactive oxygen and nitrogen species, contributing to the prevention of various cancers (lung, breast, esophageal, stomach, liver, prostate). Catechins also support cardiovascular health, modulate immune responses, and may have antibacterial and antidiabetic effects (Rashidinejad et al., 2021). However, their bioavailability can be limited by poor stability and absorption, which is an area of ongoing research for functional food applications (Jin et al., 2023). 3 Biosynthetic Pathways of Catechins 3.1 Overview of the phenylpropanoid and flavonoid biosynthesis pathways Catechins in Camellia sinensis are synthesized via the phenylpropanoid and flavonoid pathways. The process begins with phenylalanine, which is converted through a series of enzymatic steps into flavonoid intermediates, ultimately leading to the production of catechins. These pathways involve multiple gene families and are tightly regulated at both the transcriptional and post-transcriptional levels (Zhu et al., 2025). 3.2 Key structural genes involved in catechin biosynthesis Key structural genes in catechin biosynthesis include phenylalanine ammonia-lyase (PAL), 4-coumarate:CoA ligase (4CL), chalcone synthase (CHS), chalcone isomerase (CHI), flavanone 3-hydroxylase (F3H), dihydroflavonol 4-reductase (DFR), leucoanthocyanidin reductase (LAR), and anthocyanidin reductase (ANR) (Kausar et al., 2020; Zhu et al., 2025). Recent research has identified DFR as an important regulatory factor in controlling flux through the catechin pathway (Kausar et al., 2020). Further, genes CsCHIc, CsF3'H, and CsANRb have been implicated to be responsible for catechin content, and transcription factors MYB, bHLH, and MADS are regulatory (Wang et al., 2018). For galloylated catechins, some acyltransferases and galloyltransferases are also involved (Jin et al., 2023; Zhu et al., 2025) (Figure 1).
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