Determination of Epigallocatechin gallate (EGCG) and Caffeine in Domestic Tea Products using TLC-Densitometry

Abstract

Background: Tea leaves are processed to produce black tea products and green tea products. Green tea is produced from the leaves without going through an enzymatic oxidation process while black tea undergoes a thorough enzymatic oxidation process. The enzymatic oxidation process can reduce the EGCG concentration in tea products. Aim and objectives: This study aims to determine the concentration of EGCG and caffeine simultaneously in domestic green tea and black tea product of bag packaging using validated TLC-densitometry. Methods: Silica gel GF254 TLC-plate was used as a stationary phase. The optimization of the mobile phase was carried out using a variety of organic solvents such as methanol, chloroform, ethyl acetate, n-butanol, and formic acid. The EGCG and caffeine were extracted from tea products with 40 mL of water at 80oC for 40 minutes with stirring and the analytes in water extract was re-extracted with ethyl acetate. The EGCG and caffeine in ethyl acetate extract were determined using validated TLC-densitometry. Results: The mobile phase that optimally separate EGCG and caffeine with the nearest eluted analytes was chloroform: ethyl acetate: n-butanol: formic acid (20:10:7:3). The EGCG content in five green tea and black tea samples were in the range of (16.24-23.75) mg/g and (1.10-1.90) mg/g, respectively. Whereas the caffeine content in the same sample was in the range of (6.58-7.80) mg/g and (3.83-6.20) mg/g, respectively. Conclusion: The TLC-densitometry method for the determination of EGCG and caffeine in the green tea and the black tea fulfilled the validation requirements for selectivity, linearities and accuracy. The precision for caffeine determination fulfilled the AOAC requirements, while the precision for EGCG determination of in green tea (5.23%) and black tea (7.87%) exceeded the AOAC requirement. TLC-densitometry of the extracts showed that the EGCG content in green tea was higher than in black tea, while caffeine content was relatively the same on both samples.