Influence of Thermophilic Microorganism on Non-Volatile Metabolites During High-Temperature Pile-Fermentation of Chinese Dark Tea Based on Metabolomic Analysis

Pile-fermentation is a critical procedure for producing Chinese dark tea, during which thermophilic microorganisms would play an irreplaceable role. However, there have been little researches on the influences of thermophilic microorganism pile-fermentation (TMPF) in high-temperature of Chinese dark tea. Thus, we conducted high-performance liquid chromatography and nontargeted metabolomic to analyze the non-volatile metabolites of TMPF. Our results discovered that the amounts of ( −)-epigallocatechin gallate, ( −)-epigallocatechin, ( −)-epicatechin gallate, and ( −)-epicatechin were decreased significantly ( p < 0.05) after TMPF. By using nontargeted metabolomic analysis, a total of 1733 ion features were detected. KEGG pathway enrichment analysis showed that TMPF had a significant impact on caffeine metabolism. Also, theophylline, 3-methylxanthine, and 1,3,7-trimethyluric acid were increased significantly after TMPF, which suggested that demethylation and oxidation reaction might be the main pathways of caffeine metabolism. This study provides a better understanding of the mechanism of TMPF during high-temperature for Chinese dark tea and lays a foundation for further research.