Catechins

Catechins are the molecular workhorses of tea, responsible for astringency, antioxidant capacity, and much of tea's health-promoting activity. Fresh tea leaves contain catechins at 20-30% of dry weight, with EGCG as the dominant form followed by EGC, ECG, and EC. During oxidation in black tea production, the enzyme polyphenol oxidase catalyzes the conversion of catechins into larger molecules: theaflavins (responsible for briskness and bright color) and thearubigins (responsible for body and depth). This transformation is why green tea tastes astringent and grassy while black tea tastes smooth and malty — the underlying catechin chemistry has fundamentally changed. Catechin content varies by cultivar, season, altitude, and leaf maturity. Spring-harvested, high-altitude, shade-grown leaves of small-leaf cultivars tend to have the highest concentrations. Beyond antioxidant activity, catechins have demonstrated antimicrobial properties — traditional Chinese medicine long used strong green tea as a wound wash. Modern research continues to explore catechins' potential roles in cardiovascular protection, weight management, and cognitive health.