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 hydrol ysing and analysing flavonols in tea leaves and tea infusions are optimised and an isocratic elution system for the determination of the hydrolysed fl avonols by high-performance liquid chromotography is presented. Aqueous eth anol was selected as the best solution for hydrolysing flavonoids in tea le aves. The contents of flavonols on a dry weight base in green tea leaves ra nged 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, an d kaempferol, respectively. It was observed that the particle size of groun d 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.