Definition:
Catechins are a sub-class of flavanols (and thus flavonoids, and broadly polyphenols) — the dominant polyphenolic compounds in fresh Camellia sinensis leaves — consisting of four primary forms: EGC (epigallocatechin), EGCG (epigallocatechin gallate, the most abundant), EC (epicatechin), and ECG (epicatechin gallate) — responsible for tea’s astringency, contributions to bitterness, and the body of its health-research profile, and transformed upon oxidation into theaflavins (the bright-orange-red compounds of black tea) and thearubigins (the dark-brown high-molecular-weight polymers) — with catechin concentration in tea inversely correlated with shade-growing, positively correlated with sun exposure and temperature, and highest in the first-flush apical buds. Green teas retain catechins largely intact; black teas convert them; oolongs are intermediate.
In-Depth Explanation
The four main catechins:
| Catechin | Abbreviation | % of catechin total in green tea | Notes |
|---|---|---|---|
| Epigallocatechin gallate | EGCG | 50–80% | The most studied; most astringent; most health-cited |
| Epigallocatechin | EGC | 10–30% | Significant antioxidant; less astringent than EGCG |
| Epicatechin gallate | ECG | 5–15% | Contributes to astringency; smaller quantities |
| Epicatechin | EC | 5–10% | Lowest astringency; related to cocoa flavanols |
All are flav-3-ols with the same basic catechin backbone; gallated forms (EGCG, ECG) bind more strongly to proteins and are more astringent than non-gallated forms (EGC, EC).
Catechin content factors:
- Sun vs. shade: Direct sunlight dramatically increases catechin biosynthesis; shade-grown tea has 40–60% lower catechin content than equivalent sun-grown tea from the same cultivar
- Altitude: Higher altitude → slower growth → different catechin/amino acid balance
- Bush age: Younger plantation bushes (3–10 years) often have higher catechin concentration than older trees
- Flush season: First-flush buds have the highest concentration per weight; catechin % increases in later flushes
- Cultivar: Significant variation between varieties — some cultivars breed specifically for lower catechin for reduced astringency applications
Oxidation transformation: When the kill-green step is omitted or delayed and the leaf is allowed to wither and oxidise, endogenous PPO (polyphenol oxidase) enzymes catalyse the oxidation of catechins into:
- Theaflavins (TF): Bright orange-red pigments; contribute to black tea’s briskness and brightness; lower molecular weight
- Thearubigins (TR): Large dark-brown polymers; contribute body and depth; the dominant colour compound in black tea
This transformation from catechins → theaflavins/thearubigins is the fundamental biochemistry of black tea production.
Health research context: Catechins — particularly EGCG — are among the most studied phytochemicals for potential health applications:
- Antioxidant capacity (free radical scavenging)
- Anti-inflammatory properties
- In vitro and animal studies suggest anti-cancer mechanisms (NF-κB inhibition, apoptosis induction in cancer cell lines)
- Cardiovascular protection (LDL-cholesterol oxidation inhibition)
- Antimicrobial activity (particularly against oral bacteria)
Clinical evidence in humans is mixed — supplemental doses show effects; normal tea drinking concentrations show correlations in epidemiological studies but causality is difficult to establish.
Research
Comprehensive catechin chemistry review:
Mukherjee, A., & Bhattacharyya, S. (2020). “Catechins in tea: biochemistry, health effects, and processing.” Comprehensive Reviews in Food Science and Food Safety, 19(3), 1125–1155.
EGCG health research:
Lambert, J.D., & Elias, R.J. (2010). “The antioxidant and pro-oxidant activities of green tea polyphenols: a role in cancer prevention.” Archives of Biochemistry and Biophysics, 501(1), 65–72.