Determination of Theanine Enantiomers by HPLC; Comparison of Detection Methods

Theanine, a non-proteinogenic amino acid present in tea leaves, is well known for its health promoting effects such as lowering blood pressure, reducing caffeine side effects, improving memory and supporting the immunity system. Theanine occurs in dietary supplements as racemate, while they should contain only the L-enantiomer. The article deals with the optimization of separation and detection of underivatized and derivatized theanine enantiomers on a chiral teicoplanin-based stationary phase. The chromatographic limits of detection and quantification were determined with the aim to assess the content of the theanine enantiomers in dietary supplements.