Catechin metabolites after intake of green tea infusions

Green tea contains relatively large amounts of catechins, that have been recognized to be efficient free‐radical scavengers. In spite of a largely described antioxidant effect, the metabolic fate of catechins in humans has been scarcely studied. An infusion of green tea (about 400 mg of catechins) was given to healthy volunteers; plasma and urine samples were collected for 5 h and 2 days, respectively. Epigallocatechin gallate and epicatechin gallate were detected in plasma samples, reaching the maximum concentration (2 μM) at 2 h. Urine samples collected at 6–48 h contained detectable amounts of final catechin metabolites, including 4‐hydroxybenzoic acid, 3,4‐dihydroxybenzoic acid, 3‐methoxy‐4‐hydroxy‐hippuric acid and 3‐methoxy‐4‐hydroxybenzoic acid (vanillic acid). The total content of these metabolites averaged 60 mg. The levels of free plasma catechins account only partly for the increased (∼ +20%) total radical‐trapping antioxidant parameter (TRAP) detected after green tea intake. Catechin conjugates (glucuronide and sulphate) and metabolites may add further contribution and explain the measured TRAP increase.