Separation of Tannins and Caffeine in Black Tea Using Modified Microwave-Assisted Extraction and High-Performance Liquid Chromatography.

Black tea is known to contain condensed tannins including catechin (C), epicatechin (EC), and epigallocatechin gallate (EGCG), as well as caffeine (CAF). Some consumers of specific diets avoid consuming tannins or CAF. Therefore, this study aimed to explore the fast and simple development of a method for separating and quantifying tannins and CAF in black tea using microwave-assisted extraction (MAE) followed by high-performance liquid chromatography (HPLC) analysis. MAE, a type of solid-phase extraction recently developed, was used with a modified microwave that simultaneously accommodates up to 24 samples. The effects of various MAE parameters, including microwave irradiation power, temperature, and solvent, were studied, with concentrations measured in mg/kg. The results showed that optimal extraction conditions were achieved at a microwave irradiation power of 1500 W, a temperature of 80°C, and methanol as the extraction solvent. The extracted samples were analyzed using a C18-M-SE reverse phase column (150 × 4.6 mm) with a mobile phase consisting of acetonitrile, methanol, and H3PO4 (1:49:50), and NaH2PO4 (20 mM) at pH 2.5. The three tannin compounds and CAF were separated in less than 10 min. The method demonstrated excellent repeatability (RSD = 2%, n = 3), accuracy (96.7-102.5%), and was successfully applied to determine tannin content in commercial black tea samples. [ABSTRACT FROM AUTHOR]