Determination of flavonols in green and black tea leaves and green tea infusions by high-performance liquid chromatography

Tea flavonols are potent antioxidants and make up 2-3% of the water-soluble solids from tea leaves. In this paper, the conditions necessary for hydrolysing and analysing flavonols in tea leaves and tea infusions are optimised and an isocratic elution system for the determination of the hydrolysed flavonols by high-performance liquid chromotography is presented. Aqueous ethanol was selected as the best solution for hydrolysing flavonoids in tea leaves. The contents of flavonols on a dry weight base in green tea leaves ranged From 0.83-1.59. 1.79-4.05. and 1.56-3.31 g/kg, and in black tea leaves From 0.24-0.52, 1.04-3.03, and 1.72-2.31 g/kg for myricetin, quercetin, and kaempferol, respectively. It was observed that the particle size of ground tea leaves significantly influenced the yield of flavonols. The contents of flavonols in different green tea infusions are given.;(C) 2001 Elsevier Science Ltd. All rights reserved.