Analysis of catechins from green and black tea in humans: a specific and sensitive colorimetric assay of total catechins in biological fluids

Catechins are a group of flavonoids widely occurring in fruits, wine and tea, which are strong antioxidants with demonstrated anticarcinogenic effects in animal models. There is currently little knowledge on the bioavailability of catechins due to a lack of suitable analytical methods. Therefore a simple colorimetric assay was developed for the determination of the concentration of catechins in plasma. Following precipitation of proteins with methanol, tea flavonoids were accumulated by solid phase adsorption to alumina. Reactions of adsorbed catechins with 4-dimethyl amino cinnamaldehyde under strong acidic conditions results in desorption and development of a highly selective coloured complex (λ = 637 nm). The method is highly specific for catechins with equimolar responses for catechin, epicatechin, epigallocatechin, epicatechin gallate and epigallocatechin gallate. The detection limit in plasma is 0.05 μmol/L and the within and between day variation was 1.1% and 2.6%, respectively. Following consumption of a single dose of green tea, equivalent to six cups of tea, plasma levels of total catechins of 2.36 ± 0.55 μmol/L (n = 5) were reached after 60 min. This novel method is a rapid and sensitive way to gain more insight in the bioavailability of catechins from tea, wine and foods.