Determination of L-Theanine and Caffeine Contents in Tea Infusions with Different Fermentation Degrees and Brewing Conditions Using the Chromatographic Method

Abstract

This study aimed to determine the caffeine and L-theanine contents in tea infusions prepared under varying fermentation degrees, brewing conditions (temperature and time), and serving methods (tea bag/loose-leaf). Infusions of six tea types (green, white, yellow, oolong, black, and Pu-erh) and various serving forms of green, white, and black tea were brewed at 80 °C and 100 °C for 2, 5, and 10 min. Contents were analyzed using reversed-phase high-performance liquid chromatography. Caffeine levels were highest in black and yellow tea (14 ± 1.0 mg/200 mL and 13.8 ± 0.2 mg/200 mL, respectively), both of which were significantly higher than the levels in green, white, and oolong tea (11 ± 2.1 mg/200 mL; 5.8 ± 0.7 mg/200 mL; and 4 ± 1.6 mg/200 mL, respectively; p < 0.001), whereas Pu-erh tea