Distinct characteristic compounds and preventive effects on ulcerative colitis of different grades of Keemun black tea

Keemun black tea (KBT), a classic Chinese black tea with exquisite quality, was traditionally classified into seven grades. However, the chemical profiles and characteristic metabolites between the grades have not been investigated, and the grades-associated health benefits remain unexplored. In this study, metabolomics data revealed that premium grades P1 and P2, high grades T1, T2 and T3 exhibited very similar chemical profiles and clustered together, respectively. Low grades T4 and T5 formed a separate cluster. Therefore, P1 and P2 can merge into a new Premium grade; T1, T2, and T3 combine into a new First grade; and T4 and T5 group into a new Second grade. Quantitative analysis identified caffeine, ECG, rutin, propyl gallate, and vicenin 2 as grade-related metabolites. Additionally, animal experiments have shown that high-grade KBT, compared to low-grade KBT or Maofeng green tea, exhibits superior efficacy in preventing epithelial barrier damage, preserving colon length, reducing pro-inflammatory markers, increasing Firmicutes/Bacteroidetes ratio and short-chain fatty acids, and enhancing tight junction integrity in ulcerative colitis mice induced by DSS. In summary, we established a new grading system for KBT based on chemical profiles and health-values, providing important information for KBT market.