Epigallocatechin-3-gallate (EGCG)

Function

Epigallocatechin-3-gallate, commonly called EGCG, is a green tea catechin and one of the most studied polyphenols in tea leaves. It belongs to the flavan-3-ol family and is known for strong interactions with redox biology, inflammatory signaling, endothelial function, lipid metabolism, and cellular stress-response pathways.

EGCG can influence antioxidant defense systems, but its biological activity is not limited to direct free radical scavenging. It can modulate transcription factors and enzymes including Nrf2, NF-kB, AMPK, MAPK, PI3K-Akt, and proteins involved in apoptosis, autophagy, and mitochondrial regulation. These pathways affect oxidative stress responses, energy metabolism, inflammatory communication, and cellular survival.

EGCG also interacts with protein structure and membrane signaling because of its gallate group and multiple hydroxyl groups. In experimental systems, it has been studied for effects on angiogenesis, cell-cycle regulation, lipid oxidation, glucose metabolism, and immune-cell signaling. Actual effects in the body depend on absorbed metabolites, dose, food matrix, and individual metabolism.

Production

Tea plants produce EGCG through the flavonoid biosynthesis pathway. Phenylalanine-derived intermediates are converted into catechin structures, and galloylation reactions add the gallate group that distinguishes EGCG from simpler catechins.

EGCG is abundant in green tea because green tea leaves are heated soon after harvesting, limiting oxidation by polyphenol oxidase enzymes. In black tea production, catechins are more extensively oxidized into theaflavins and thearubigins, reducing intact EGCG levels.

EGCG content varies with tea cultivar, leaf age, growing conditions, processing, brewing temperature, steeping time, and storage. Hot water extraction releases EGCG into brewed tea, though prolonged heat and alkaline conditions can degrade catechins.

Regulation

EGCG bioavailability is regulated by intestinal absorption, stability in the digestive tract, methylation, sulfation, glucuronidation, microbial metabolism, and transport proteins. Circulating EGCG concentrations are typically lower than amounts present in brewed tea because metabolism and elimination are efficient.

EGCG can influence Nrf2-related antioxidant enzyme expression, support glutathione-related defense pathways, and moderate inflammatory signaling in experimental models. It may also activate AMPK-linked energy-sensing pathways and influence lipid metabolism. At high experimental concentrations, EGCG can behave as a pro-oxidant, which is why biological context matters.

EGCG is naturally consumed with other tea catechins, caffeine, theanine, flavonols, and minerals. Its nutritional role is best understood as part of the broader green tea phytochemical matrix affecting redox signaling, metabolic regulation, and cellular stress adaptation.