Biochemical Components Associated With Microbial Community Shift During the Pile-Fermentation of Primary Dark Tea

Abstract

Primary dark tea is used as raw material for compressed dark tea, such as Fu brick tea, Hei brick tea, Hua brick tea, and Qianliang tea. Pile-fermentation is the key process for the formation of the characteristic properties of primary dark tea, during which the microorganism plays an important role. In this study, the changes of major chemical compounds, enzyme activities, microbial diversity, and their correlations were explored during the pile-fermentation process. Our chemical and enzymatic analysis showed that the contents of the major compounds were decreased, while the activities of polyphenol oxidase, cellulase, and pectinase were increased during this process, except peroxidase activity that could not be generated from microbial communities in primary dark tea. The genera Cyberlindnera, Aspergillus, Uwebraunia, and Unclassified Pleosporales of fungus and Klebsiella, Lactobacillus of bacteria were predominant in the early stage of the process, but only Cyberlindnera and Klebsiella were still dominated in the late stage and maintained a relatively constant until the end of the process. The amino acid was identified as the important abiotic factor in shaping the microbial community structure of primary dark tea ecosystem. Network analysis revealed that the microbial taxa were grouped into five modules and seven keystone taxa were identified. Most of the dominant genera were mainly distributed into module III, which indicated that this module was important for the pile-fermentation process of primary dark tea. In addition, bidirectional orthogonal partial least squares (O2PLS) analysis revealed that the fungi made more contributions to the formation of the characteristic properties of primary dark tea than bacteria during the pile-fermentation process. Furthermore, 10 microbial genera including Cyberlindnera, Aspergillus, Eurotium, Uwebraunia, Debaryomyces, Lophiostoma, Peltaster, Klebsiella, Aurantimonas, and Methylobacterium were identified as core functional genera for the pile-fermentation of primary dark tea. This study provides useful information for improving our understanding on the formation mechanism of the characteristic properties of primary dark tea during the pile-fermentation process.

Keywords: Illumina MiSeq sequencing; biochemical components; food fermentation; microbial community; primary dark tea.

FIGURE 1

Changes in the major chemical compounds during the pile-fermentation process of primary dark tea. Water extract and tea polyphenol (A), amino acid, flavonoid, and soluble sugar (B).

FIGURE 2

Changes in the enzyme activities during the pile-fermentation process of primary dark tea. PPO, polyphenol oxidase; POD, peroxidase (A); CEL, cellulase; PEC, pectinase (B).

FIGURE 3

Changes in Shannon and Chao1 index of fungal (A,C) and bacterial (B,D) community during the pile-fermentation process of primary dark tea.

FIGURE 4

PCA and NMDS analysis of microbial communities in sample during the pile-fermentation process of primary dark tea. Fungal PCA (A), bacterial PCA (B), fungal NMDS (C), and bacterial NMDS (D).

FIGURE 5

Microbial taxonomic compositions showing the microbial successions at phylum: (A) fungus, (B) bacteria; order: (C) fungus, (D) bacteria; and genus: (E) fungus, (F) bacteria level during pile-fermentation process of primary dark tea. The taxonomic abundance <1% were classified into “others.”

FIGURE 6

Interaction networks in the microbial communities of primary dark tea. The nodes of network were group into five modules. The co-occurring networks are colored by phylum. The size of each node is proportion to the number of connections (that is, degree), and the red edge indicates a positive interaction and the blue edge indicated a negative interaction between two nodes. The numbers are indicated as follows: 1∼3 the module hubs bOTU8, bOTU21, and fOTU7. 4∼7 the connectors fOTU21, fOTU30, fOTU58, and fOTU162. I∼V indicated the number of modules.

FIGURE 7

Redundancy analysis (RDA) showing the relationship between microbial structure and major chemical compounds concentrations during the pile-fermentation process of primary dark tea. The red arrow indicated the compounds variances; the blue arrow indicated the important genera of microbial communities (relative abundance >0.01%). Filled circles indicated the samples during the pile-fermentation of primary dark tea. WE, water extract; TP, tea polyphenol; AA, amino acid; FLA, flavonoid; SS, soluble sugar.

FIGURE 8

Correlation analyses among microbiota, chemical compounds, enzyme activities (A) and the core microorganisms (B) in primary dark tea during pile-fermentation process.