Simultaneous determination of caffeine and 8 catechins in oolong teas produced in Thailand

A simple, rapid and reliable method of high performance liquid chromatography (HPLC) was developed for the simultaneous determination of bioactive compounds in oolong teas. The optimized method consisted of the use of a C18 reversed-phase column, an isocratic elution system (2 ml/min) of water:acetonitrile (87:13) containing 0.05% trifluoroacetic acid and the detection wavelength of 210 nm. The developed system sufficiently separated (-)-gallocatechin (GC), (-)-epigallocatechin (EGC,), (+)-catechin (C), (-)-epicatechin (EC), (-)-epigallocatechin gallate (EGCG), caffeine (CF), (-)-gallocatechin gallate (GCG), (-)-epicatechin gallate (ECG) and (-)-catechin gallate (CG) within 12 min elution time at 30oC. This HPLC method had been proved to be appropriate for the identification and quantification of caffeine and 8 catechins, and exhibited good correlation coefficients, detection levels, precision and recovery rates. The developed analytical method was subsequently applied for determination of these bioactive compounds in 17 oolong teas produced in Thailand. Analysis under the optimized conditions revealed that the contents of caffeine and total catechin were 2.25±0.48 and 9.92±1.46 g/100 g DW, respectively. The levels of EGC (2.87±0.75 g/100 g DW) and EGCG (2.60±0.66 g/100 g DW) were the highest among quantified catechins.