Abstract
Free amino acids are closely related to the savory taste and beneficial effects of tea, and high-performance liquid chromatography (HPLC) is the most widespread analytical approach for simultaneous determination of free amino acids in tea. However, the reported HPLC methods have drawbacks such as long run times, low resolution, or poor efficiency. In this study, a special amino acid analysis column was used to separate and verify 21 amino acids including l-theanine, the predominant amino acid in tea. The mobile phases, including the sodium acetate and acetic acid concentration in buffer B, and the pH and concentration of sodium acetate in buffer A were optimized. The elution gradients were optimized using DryLab 2000 Plus software. In this way, an online o-phthaldialdehyde precolumn derivatization HPLC-fluorescence detection method was developed for simultaneous determination of 21 amino acids. Comparison to other HPLC methods for simultaneous determination of free amino acids in tea showed that our method is easy (automated derivatization), quick (30 min), inexpensive, and green (using a minimum of solution). It has good resolution (≥1.8) and high selectivity (interpark time ≥ 0.5 min). Free amino acids in six tea samples were analyzed. This work provides an HPLC method to simultaneously measure 21 amino acids in tea and potential in other food products.
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