Theanine and Caffeine Content of Infusions Prepared from Commercial Tea Samples

BACKGROUND: Caffeine and L-theanine are pharmacologically important constituents of tea, especially due to their effects on the central nervous system. The effects of these two compounds are opposite: While caffeine is a well-known stimulant, theanine has a relaxing effect. Tea processing may influence the caffeine and theanine content of tea leaves. OBJECTIVE: The aim of our work was to quantify these constituents from a set of commercial products to reveal the possible correlations of caffeine and theanine content and processing methods. MATERIALS AND METHODS: Theanine and caffeine contents of 37 commercial white, green, oolong, black, and pu-erh tea samples were quantified by high-performance liquid chromatography-diode array detector. RESULTS: The mean L-theanine content of white, green, oolong, and black teas were 6.26, 6.56, 6.09, and 5.13 mg/g, respectively. The same values for caffeine content were 16.79, 16.28, 19.31, and 17.73 mg/g. CONCLUSION: Though the effect of processing on theanine content was evident, quantification for these analytes does not seem to be a good criterion to discriminate the different types of tea. Caffeine content provided no information on the effect of processing, and the theanine content of the samples was rather variable, independently from the type of the tea. The quantitative analysis of caffeine and theanine is essential to assess the stimulating effect of the tea, however, for chemical profiling further secondary metabolites have to be determined. SUMMARY: Thirty-seven commercial white, green, oolong, black, and pu-erh tea samples were analyzed for caffeine and theanine content. While the caffeine content was similar, the theanine contents of black teas were slightly lower and practically zero in pu-erh. The great variability of these two compound within the tea categories allows no discrimination of tea types based solely on theanine and caffeine quantification. Contrary to the previous data, the way of processing has no determining effect on theanine content. Abbreviations used: CZE: Capillary zone electrophoresis, DAD: Diode array detector, EEG: Electroencephalography, GC: Gas chromatography, HPLC: High-performance liquid chromatography, IR: Infrared spectroscopy, MEKC: Micellar electrokinetic capillary chromatography, MS: Mass spectrometry, RP: Reversed phase, RSD: Relative standard deviation, SD: Standard deviation, TLC: Tile liquid chromatography, UV: Ultraviolet