Metabolomics, sensory evaluation, and enzymatic hydrolysis reveal the effect of storage on the critical astringency-active components of crude Pu-erh tea

Crude Pu-erh tea (CPET) is distinct from ripened Pu-erh tea, and usually needs a long-term aging under natural conditions, which can make it taste more mellow. In the present study, metabolomics integrated with sensory evaluation was used to investigate the key astringency compounds of CPET during storage. Metabolomics results showed that these CPET samples could be classified into two groups, one was storage from 1 to 5 years, and the other was 6–8 years. Meanwhile, non-galloylated catechins, hydroxycinnamic acids, flavonol glycosides, and gallotannins were marker compounds, which were responsible for distinguishing short and long aging time. Correlation coefficients between astringency scores and (–)-epigallocatechin, (–)-epicatechin, quercetin-glucose, myricetin-glucose, and (–)-gallocatechin gallate were 0.826, 0.821, 0.815, 0.811, and 0.718, respectively. The astringency contribution of galloylated catechins and flavonol glycosides was also investigated by treating CPET infusion with tannase and β-glycosidase. The tannase treatment greatly reduced the contents of galloylated catechins, and correspondingly decreased the astringency scores. β-Glycosidase could hydrolyze the flavonol glycosides into flavonol aglycones, but the astringency intensity of CPET infusion was not affected. These results suggested hydrolysis of galloylated catechins was the key reason for astringency decrease during storage of CPET, while flavonol glycosides comparatively contributed less to the astringency.