EVALUATION OF TEA FUNCTIONALITY: DETERMINATION OF L-THEANINE CONTENT IN GREEN AND BLACK TEAS BY LIQUID CHROMATOGRAPHY

Abstract

L-theanine (γ-glutamyl-L-ethylamide) is a free amino acid classified as functional ingredient because it has shown relevant pharmacological effects such as improving the brain ability to concentrate, learn and memorize. L-theanine is found almost exclusively in tea plants, and its final concentration in commercial tea products mainly depends on the type of raw materials and productive process. Thus, tea infusions could only be considered as functional beverage with respect to L-theanine if an adequate number of tea cups posses the necessary content to produce the desire effect. The objective of this work was to evaluate the functionality of teas marketed in Chile regarding its L-theanine content. A high performance liquid chromatographic method with ultraviolet detection (HPLC/UV) was optimized and validated to quantify L-theanine content in tea infusions. Chromatographic separation was carried out using a mixture of water and phosphoric acid (99.9: 0.1% v/v) as mobile phase and C 18 Purospher Hibar-STAR (250 mm x 4.6 mm, 5 μm) column. Detection was performed at 210 nm. The L-theanine content in teas marketed in Chile ranged from 4.21 to 24.83 (2.21 to 12.42 mg g-1), with a mean value of 10.06 mg in 200 mL (5.03 mg g-1). Considering the effective dose reported, only one brand (black tea) presented an adequate L-theanine content to produce the desired effect (two serving cups). Therefore, it is possible to conclude that most teas marketed in Chile do not have an adequate L-theanine content to be considered as functional beverage regarding this amino acid.