Composition characteristics of amino acids in Chinese teas based on large-scale samples: Origin, tea category, and harvest season

Amino acids are key contributors to the flavor of tea, and their levels and types vary depending on processing methods, growing regions, and harvest times. Despite their importance, comprehensive studies on these factors remain limited. Here, this study aims to systematically characterize the distribution and influencing factors of 32 free amino acids across major tea categories. A total of 2983 tea samples representing 7 types including green, yellow, white, black, oolong, dark and raw Pu-erh teas were analyzed based on cation-exchange chromatography with post-column derivatization using ninhydrin with multivariate statistical analysis to assess the effects of processing, origin, and harvest season. This study is the first to compare the total amount of 32 amino acids across seven tea categories. Yellow tea showed the highest levels, followed by white, green, black, raw Pu-erh, oolong, and dark tea. Low fermentation teas have higher levels of umami amino acids like theanine and glutamic acid. The total amino acid content ranks as Jiangnan > Jiangbei > Southwest > South China tea regions. Spring tea exhibited the highest total amino acid content, significantly exceeding that of summer and autumn teas. L-Tryptophan and L-Methionine levels were notably higher in summer than in spring, while β-Alanine increased significantly during autumn compared to spring and summer. These findings provide a deeper understanding of the role amino acids play in shaping tea flavor and offer valuable insights for improving tea quality and refining processing techniques.