Abstract: Changes in amino acids and polyphenols in leaves and stems during withering are critical for the formation of the material basis of tea flavor. This study systematically analyzed the differential accumulation patterns of amino acids and polyphenols in tea leaves and stems , as well as their changes during withering. The results show that the phenol-ammonia ratio in the leaves (4.66-6.36) was higher than that in the stems (1.97-2.59) during withering. The free amino acid content in tender stems (7.44%) was significantly higher than that in fresh leaves (2.22%). A total of 44 amino acids and their derivatives show differential accumulation between the two tissues, of which three (theanine, aminobutyric acid, and pipecolic acid) were found to be highly accumulated in the stems. No significant difference in total tea polyphenol content was observed between fresh leaves and tender stems. However, 97 polyphenolic compounds show differential accumulation between the two tissues. Gallate-type catechins and most flavonols and flavonol glycosides were more highly accumulated in the leaves, whereas non-gallate-type catechins were more abundant in the stems. During the withering process, the total content of free amino acids increased in the leaves but it continued to decrease in the stems. A total of 21 and 15 amino acids and derivatives underwent significant changes during the withering process in leaves and stems, respectively. The changing trends of tea polyphenol content in leaves and stems were relatively consistent, with 49 and 35 polyphenolic compounds showing significant changes during withering, respectively. The results of this study indicate that the leaf-stem ratio in tea raw materials plays a critical role in the formation of tea quality during subsequent processing, providing a theoretical basis for the development of withering regulation technologies based on leaf-to-stem ratio considerations.

Key words: metabolomics, withering, leaf and stem, free amino acids, tea polyphenols