Definition:
EGCG (epigallocatechin gallate, C₂₂H₁₈O₁₁, molecular weight 458.4) is the predominant catechin polyphenol in Camellia sinensis — constituting 50–80% of total catechin content in green tea and roughly 5–12% of dry leaf weight in typical green teas — the primary source of tea’s astringency through its strong binding to salivary proteins, and the most comprehensively researched tea compound in scientific literature, with over 10,000 published studies examining its antioxidant, anti-inflammatory, antimicrobial, and anti-tumour properties in in vitro, animal, and human contexts. EGCG is found at highest concentrations in green tea; oxidised to theaflavins and thearubigins in black tea; partially preserved in oolong.
In-Depth Explanation
Chemical structure and properties:
EGCG belongs to the flavan-3-ol subclass of flavonoids. Its structure features a three-ring flavanol backbone with multiple hydroxyl groups (responsible for antioxidant activity) and a galloyl ester group on the 3-position (responsible for the strong protein-binding that creates astringency). The “epi” prefix refers to the stereochemical configuration of its hydroxyl groups.
EGCG content comparison across tea types:
| Tea type | EGCG content (mg per 200ml cup) | Notes |
|---|---|---|
| Matcha | 60–140mg | Whole leaf consumed; highest per serving |
| Gyokuro | 30–60mg | High catechin despite shade; high extraction |
| Sencha (high grade) | 40–80mg | Full catechin extraction at right temp |
| Oolong | 15–50mg | Partial oxidation; variable by type |
| Black tea | 5–15mg | Mostly converted to theaflavins |
| Herbal (non-Camellia) | 0 | No catechins |
Primary research areas:
Anti-cancer research (in vitro and animal):
EGCG is one of the most studied phytochemicals in cancer research. Mechanisms identified in laboratory contexts include:
- Inhibition of cancer cell growth (NF-κB pathway modulation)
- Induction of apoptosis in multiple cancer cell lines
- Inhibition of angiogenesis (tumour blood vessel formation)
- Interference with specific kinase signalling pathways
Critical caveat: In vitro and animal study results have produced enormous research interest but do not straightforwardly translate to human clinical efficacy at dietary concentrations. Epidemiological studies show modest correlations between green tea consumption and cancer risk reduction in some populations but not others. Supplemental EGCG doses used in research (200–800mg) are higher than typical 2–3 cup/day dietary intake. Clinical trials have had mixed results.
Cardiovascular research:
- LDL cholesterol oxidation inhibition (reducing atherogenic potential)
- Endothelial function improvement (vasodilation)
- Blood pressure modulation in some studies
Antimicrobial activity:
EGCG demonstrates antimicrobial activity against oral bacteria (Streptococcus mutans — a caries-causing bacterium), H. pylori, and several other pathogens in in vitro conditions.
Neuroprotective research:
Animal studies suggest potential protective effects against neurodegenerative protein aggregation (Alzheimer’s-associated amyloid beta plaques). Human clinical data limited.
Bioavailability: A significant limitation of EGCG research is low oral bioavailability — EGCG is partially degraded in the alkaline environment of the small intestine, and its metabolic derivatives (rather than EGCG itself) appear to be the active forms absorbed. This complicates extrapolation from high-dose in vitro studies to real dietary consumption.
Research
Comprehensive EGCG health review:
Khan, N., & Mukhtar, H. (2013). “Tea polyphenols in promotion of human health.” Nutrients, 5(2), 507–541. Systematic review covering mechanisms across cancer, cardiovascular, metabolic, and neuroprotective research.
Bioavailability study:
Nakagawa, K., et al. (2009). “Plasma absorption and urinary excretion of EGCG from green tea: influence of food matrix.” Journal of Nutrition, 139(2), 285–291. Addressed the critical bioavailability question.