Effects of fermentation time and shooting period on amino acid derivatives and free amino acid profiles of tea

Abstract

This study aimed to investigate the effect of oxidation on free amino acids and their derivatives in tea. Oolong tea samples, oxidized for 0, 10, 30, and 60 min, green tea, and black tea were produced from the same batch of fresh tea leaves. Effects of shooting periods on free amino acids and their derivatives were also evaluated in this study. Free amino acids and their derivatives were extracted with water and analyzed by LC-MS/MS. It was observed that total amino acid content of teas in the first shooting period (16231 ± 241 μg/g-31391 ± 2034 μg/g) was higher than the second (9635 ± 379 μg/g-11665 ± 426 μg/g) and third (13937 ± 360 μg/g-17661 ± 1359 μg/g) shooting periods. Content of most amino acids including gamma aminobutyric acid (GABA) in black and oolong teas were higher than those of green tea. However, theanine contents of black and oolong teas were lower than that of green tea. Kynurenine, kynurenic acid, quinolinic acid, dopamine, tyramine, phenylethylamine and tryptamine were found in all tea samples. Kynurenic acid content was the highest (1 ± 0.1 μg/g-3±0.4 μg/g) in green, oolong and black tea samples. Concentrations of kynurenine, kynurenic acid, quinolinic acid, and dopamine were mostly found to be higher in green tea than black tea.