Effects of Pile-Fermentation Duration on the Taste Quality of Single-Cultivar Large-Leaf Dark Tea: Insights from Metabolomics and Microbiomics

Abstract

The pile-fermentation conditions and raw materials used play a vital role in determining the stability and quality of dark tea. In this study, sensory quality evaluation, metabolomics, and microbiomics techniques were used to investigate the effect of pile-fermentation duration on the taste quality of single-cultivar large-leaf dark tea (SLDT) and its underlying metabolite and microbial mechanisms. The study revealed that a 60-day duration resulted in a better SLDT sensory quality, with astringency and bitterness significantly reduced and sweetness increased. Catechins and theaflavins with ester structures, L-epicatechin, methyl gallate, protocatechuic acid, gallic acid, salicin, chlorogenic acid, and neochlorogenic acid were key taste metabolites contributing to the reduction of astringency and bitterness. Salicylic acid and D-sorbitol helped form the sweetness. Correlation analysis found out Aspergillus, Thermomyces, Bacillus, Staphylococcus, and Micrococcaceae were core functional microorganisms linked to these metabolites, helping to foster the higher quality of SLDT. Microorganisms shaped the taste quality of SLDT through metabolic processes and enzyme secretion during pile-fermentation. This study provided insights into the metabolite basis and microbiological mechanisms of SLDT taste formation and offered guidance for optimizing production processes to improve the stability and quality of dark tea.

Keywords: dark tea; metabolomics; microbiomics; pile-fermentation; quality; taste.

Figure 1

Quality characteristics of tea samples. (A) Sensory quality evaluation results, including five aspects of tea (appearance of tea leaves and leaf base, color, aroma, and taste of tea infusion) and overall scores. (B) L* values of tea infusions. (C) a* values of tea infusions. (D) b* values of tea infusions. Compared to Day 0, **: p < 0.01, ***: p < 0.001.

Figure 2

Profiles of tea metabolites. (A) PCA score plot of tea samples (sample MIX was the QC sample). (B) Clustering heat map of overall metabolites. (C) Peak area intensities of flavonoids. (D) Peak area intensities of phenolic acids. (E) Peak area intensities of amino acids. (F) Peak area intensities of organic acids. (G) Peak area intensities of alkaloids. (H) Classification chart of differential metabolites. (I) Classification chart of differential taste metabolites.

Figure 3

Profiles of differential metabolites. (A) Upset plot for overall layout of differential metabolites during PF process. (B) Venn diagram of differential metabolites during the early stage. (C) Venn diagram of differential metabolites during the middle stage. (D) Venn diagram of differential metabolites during the late stage. (E) K-means cluster plots of differential metabolites.

Figure 4

Comparison of microbial community structures. (A) PCA of fungi. (B) PCA of bacteria. (C) Relative abundance column cumulative plots of fungi at the phylum level. (D) Relative abundance column cumulative plots of fungi at the family level. (E) Relative abundance column cumulative plot of bacteria at the phylum level. (F) Relative abundance heat map of bacteria at the family level.

Figure 5

Correlation analysis of microbial communities and 31 significantly differential taste metabolites. (A) Correlation chord chart of fungi. (B) Correlation chord chart of bacteria. Pink color indicates positive correlation, blue color indicates negative correlation.