The Impact of Citrus-Tea Cofermentation Process on Chemical Composition and Contents of Pu-Erh Tea: An Integrated Metabolomics Study.

Ya Xu,Jing Zhang,Liang Zhang,Ming-Jiong Gong,Wen Xu,Xiao-Hui Qiu,Pu-Lin Liang,Zhi-Hai Huang,Xue-Lian Chen

doi:10.3389/fnut.2021.737539

Abstract

Ganpu tea, an emerging pu-erh compound tea, which is cofermented with the peel of Citrus reticulata “Chachi,” has been widely favored by Chinese consumers due to its potential health effects and distinct flavor and taste. So far, the influence of this cofermentation procedure on the chemical profile of pu-erh tea has barely been addressed yet. In this work, an ultra-high-performance liquid chromatography-Q Exactive Orbitrap mass spectrometry (UHPLC-QE Orbitrap MS)-based qualitative and quantitative method combined with multivariate analysis was conducted to comprehensively investigate the chemical changes in pu-erh tea after cofermented with Citrus peel. A total of 171 compounds were identified based on a three-level strategy, among which seven phenolic acids, 11 flavan-3-ols, and 27 flavonoids and flavonoid glycosides were identified from pu-erh tea for the first time. Eighty-nine main constituents were selected for further quantitative analysis using a validated method. Both the principal component analysis (PCA) of untargeted metabolomics and orthogonal partial least squares discriminant analysis (OPLS-DA) models of targeted components revealed the significant chemical profile disparity between the raw pu-erh tea and Ganpu tea. It showed that Citrus tea cofermentation process significantly decreased the total contents of phenolic acids, flavan-3-ols, and flavonoid aglycones, while most of the quercetin glycosides and myricetin glycosides as well as the vitexin were significantly increased. In addition, hesperidin, a flavonoid glycoside only existed in Citrus, was first found in pu-erh tea after cofermented with Citrus. This study clearly profiled the chemical composition and content changes of pu-erh tea after cofermented with Citrus peel, which revealed that Citrus tea cofermentation process further accelerated the fermentation of pu-erh tea and improved the unique flavor of tea.

Highlights

Pu-erh tea, is a representative postfermented tea in China
The typical total ion chromatograms (TICs) of Ganpu tea and PE were illustrated in Figure 2, where the disparity in the relative peak height and peak area can be concluded by visual inspection
Based on the qualitative analysis strategy, a total of 171 compounds were identified or tentatively characterized, including phenolic acids, flavan-3-ols, flavonoids/flavonoid glycosides, and others, 31 of them were confidently identified according to the standards, 94 were tentatively identified according to literature data, and 45 of them were putatively identified as potential new compounds based on level 3 (27 flavonoids, 11 flavan-3-ols, and seven phenolic acids) (Supplementary Table 3)

Summary

Introduction

Pu-erh tea (pu’er, or pu-er, PE), is a representative postfermented tea (dark tea) in China. The Sheng pu-erh would be subjected to aging naturally for several years, resulting in a slow fermentation. This time-consuming method was substituted in industry scale by a style of processing approach called pile-fermentation, which involves the application of heat and moisture, as well as the inoculation of the tea leaves with beneficial bacteria to expedite the natural aging process. This pile-fermented dark tea is called Shou pu-erh tea (ripen pu-erh tea)

Methods

Results

Conclusion