Quality-related Metabolites in Chunlü Green Tea Affected by Varied Withering in Processing

Objective Effect of varied withering during processing on the quality-related metabolites in Chunlü green tea was determined.

Method Fresh leaves with one bud and two leaves in spring were plucked from Chunlü bushes to make the green tea. Withering the leaves to result in a 10% water loss (WL-10) or 25% water loss (WL-25) was applied in the conventional process to produce 5 sets of finished tea samples, FT-10 and FT-25, respectively, for a metabolomic comparison. Ultra performance liquid chromatography-tandem mass spectrometry was employed for chemical analysis, and multivariate statistical analysis for principal components determination.

Result Of the differential metabolites between the teas, organic acids constituted the highest proportion that included 26.66% were down-regulated and 12.37% up-regulated. Amino acids and derivatives were second most abundant with 13.19% being down-regulated and 19.40% up-regulated. The third predominant metabolite category was flavonoids that had 8.71% of them down-regulated and 6.74% up-regulated. There were 399 down-regulated and 291 up-regulated metabolites that were different between WL-10 and WL-25. And between FT-10 and FT-25, 81 were down-regulated and 101 up-regulated. The KEGG enrichment analysis on WL-10 and WL-25 showed the top 10 pathways to be associated with tryptophan metabolism, phenylalanine, tyrosine and tryptophan metabolism, amino acid biosynthesis, sesquiterpene and triterpene biosynthesis, etc. Whereas on FT-10 and FT-25, the 182 differential metabolites distributed across 64 metabolic pathways, with 7 most enriched pathways being phenylalanine metabolism, diterpene biosynthesis, biosynthesis of secondary metabolites, and sesquiterpene and triterpene biosynthesis.

Conclusion The different withering that removed varied amounts of moisture in the leaves produced green teas with significant variations in sensory quality-related metabolites. Identification of these substances and associated metabolic pathways would be of value for process optimization of Chunlü green tea.