Microbial Succession and the Dynamics of Chemical Compounds during the Solid-State Fermentation of Pu-erh Tea

Yan Ma,Xiaoqin Su,Shuangmei Duan,Ming Zhao,Caiyou Lv,Donglian Zhang,Dongying Zhang

doi:10.3390/app7020166

Abstract

An in-depth knowledge of the microbiota and metabolites in the solid-state fermentation (SSF) of Post-fermented Pu-erh tea (Pu-erh Shucha, PFPT), a Chinese traditional tea with various health benefits, is essential to develop modern fermentation technology. In this work, the microbial diversity and succession in two laboratory-developed SSF protocols for PFPT were investigated using pyrosequencing analyses of the bacterial 16S rRNA and fungal 18S rRNA genes. The active bacteria in the initial stages of SSF (seven days) were from the raw materials and environment, with a dominance of Proteobacteria in both the raw materials and SSF after seven days. The environmental bacteria were inoculated into the tea mass throughout the fermentation process and multiplied, with a dominance of Firmicutes at day 14 and 21, and then Firmicutes and Actinobacteria at the last stages of fermentation (day 28 and 35). The dominant fungi came from the raw material and were identified at the genus level as Aspergillus throughout the SSF process. The contents of tea polyphenols, free amino acids, gallic acid, theaflavin, thearubigin, and catechins decreased significantly (p < 0.05), while the level of theabrownin increased significantly (p < 0.05). The caffeine content showed no significant change (p > 0.05). In total, 30 bacterial and three fungal genera showed significant correlations to 1–8 and 3–4 identified tea compounds, respectively (p < 0.05). The dynamics of the microbiota and chemical compounds, and correlations between their changes in the SSF of PFPT were revealed, and present a foundation for further studies on the microbial effects on chemical compounds.

Highlights

Post-fermented Pu-erh tea (Pu-erh Shucha, PFPT) is a well-known traditional Chinese tea with special sensory characteristics including mellow taste, stable flavor, and brownish-red color [1].Additional, in vivo, in vitro, and clinical studies have suggested that PFPT has multiple health benefits, such as hypolipidemic, antiobesity, antimutagenic, antioxidative, antitumor, free radical scavenging, and toxicity-suppressing activity [2]
tea polyphenols (TPs), free amino acids (FAA), EGC, EC, epigallocatechin 3-O-gallate (EGCG), GG, epicatechin 3-O-gallate (ECG), gallic acid (GA), TF, and TR decreased significantly (p < 0.05), and contents of TB increased significantly (p < 0.05). These changes in the chemical compounds during the solid-state fermentation (SSF) of PFPT were in accord with the previous reports of Gong [15], Lee [16], and Qin [17]
By using a 16S rRNA gene clone library, we demonstrated that the dominant bacteria during SSF of PFPT were Proteobacteria and Firmicutes [7]

Summary

Introduction

Post-fermented Pu-erh tea (Pu-erh Shucha, PFPT) is a well-known traditional Chinese tea with special sensory characteristics including mellow taste, stable flavor, and brownish-red color [1]. Additional, in vivo, in vitro, and clinical studies have suggested that PFPT has multiple health benefits, such as hypolipidemic, antiobesity, antimutagenic, antioxidative, antitumor, free radical scavenging, and toxicity-suppressing activity [2]. It is popular in Southeast Asia and has been introduced to the Western marketplace in recent years. Unlike the raw material of black tea, fresh tea leaves [3,4], the raw materials of PFPT are sun-dried green tea (a variety of green tea products) produced from Camellia sinensis var. In PFPT manufacturing, the post-fermentation process is crucial.

Methods

Results

Conclusion